Meet 10 of the weirdest and most wonderful tropical fish in the aquarium world. From the ghostly Black Ghost Knifefish and curious Elephantnose to surface-hunting Archerfish, quirky Puffers and magnificent Arowana, these are no ordinary community fish. Discover what makes each species extraordinary, the environments they need to thrive, what they eat, and why choosing compatible tankmates takes more than simply picking your favourites.

There are some fish you admire as they swim past in an aquarium shop—and then there are the ones that make you stop in your tracks.

Perhaps it is the almost ghostly movement of a Black Ghost Knifefish, gliding forwards, backwards and seemingly sideways without the obvious movement we expect from a fish. Perhaps it is an Elephantnose carefully investigating the bottom of the aquarium with its extraordinary elongated lower jaw. Or perhaps an African Butterflyfish is hovering almost motionless at the surface, looking as though it belongs to another age entirely.

These are the fish I have always found fascinating.

During my years in the pet industry, specialty tropical fish were a particular interest of mine. They are unusual, often incredibly beautiful and endlessly interesting to observe. But they also taught me something very important: the more unusual the fish, the more important it becomes to understand the animal before bringing it home.

This isn't a beginner's guide.

The fish we're going to meet in this article are better suited to intermediate and experienced fish keepers who already understand the basics of water quality, filtration, the nitrogen cycle, aquarium maintenance and recognising when something isn't right. Some of these species grow much larger than people expect. Some are predators. Some have specialised diets or sensory systems. Some require particular water conditions, subdued lighting or carefully designed environments. And some can be quite expensive.

That doesn't mean they are impossibly difficult to keep. In the right hands, many can be wonderful aquarium inhabitants. But buying an unusual fish because it looks spectacular in the shop and then trying to work out what it needs afterwards is never a good approach.

With specialty fish, research should always come before purchase.

Throughout this article, we'll look at ten weird and wonderful freshwater tropical fish in detail. We'll explore where they come from, how they behave in the wild, their preferred pH, temperature and water conditions, what they naturally eat, how large they become, the aquarium they really need and which other fish—if any—they can safely live with.

We'll also answer some of the questions people actually ask when they see these fish:

Can I put that with my Neon Tetras? Will it eat my other fish? Why does it hide all day? Can I keep several of these unusual species together? How big is that tiny fish in the shop actually going to become?

Most importantly, we'll look beyond simply keeping these animals alive.

The aim should always be to create an environment in which the fish can behave like the fish it was meant to be.

Understanding the Fish Before Designing the Aquarium

One of the most interesting things about specialty fish is that their appearance and behaviour often tell us a great deal about the environments in which they evolved.

A fish that spends its life close to the surface has very different needs from one that searches through the riverbed for food. A nocturnal fish doesn't experience its world in the same way as a brightly coloured species that is active in daylight. A fish that naturally shelters amongst submerged roots, branches and vegetation shouldn't be expected to feel comfortable in a brightly illuminated, almost empty aquarium simply because that arrangement makes it easier for us to see it.

This is where I believe we need to turn traditional aquarium thinking around.

Instead of choosing a fish to suit the aquarium we've already decorated, we should be asking:

What would make this particular fish feel secure enough to behave naturally?

That doesn't mean trying to reproduce a South American river or an African wetland perfectly in your lounge room. It means understanding the important elements of the fish's natural environment and recreating those elements wherever practical.

For one species, that might mean fine sand for natural foraging. For another, it could mean floating plants and a calm surface. Others may need driftwood, dense planting, caves, shaded areas, open swimming space or a combination of several different habitats within one large aquarium.

Lighting matters too. We naturally want to see the beautiful fish we've paid good money for, but illuminating a naturally shy or nocturnal species under intense light all day can have exactly the opposite effect—it may spend most of its time hiding.

The answer isn't to remove its hiding place.

The answer is to create better hiding places.

We can use aquarium-safe caves, tunnels, driftwood, rocks and dense planting to create areas where a fish feels protected while still allowing opportunities to observe it. Sometimes a purpose-made transparent aquarium shelter, carefully surrounded by plants and other cover, can work particularly well for a species that likes to retreat into a tube or cavity. The fish gains the security of an enclosed space while we may still be able to quietly watch it without disturbing it.

The important word here is aquarium-safe. Random pieces of glass, bottles, pipes, rocks or timber shouldn't simply be added because they look suitable. Anything placed in an aquarium needs to be safe for the water, free from contaminants and sharp edges, and appropriately sized so the fish cannot become trapped or injured.

This philosophy will follow us throughout the article:

Natural habitat → natural behaviour → aquarium design.

Once we understand why a fish behaves as it does, many of the supposedly strange things it does in captivity suddenly aren't strange at all.

And there is perhaps no better fish with which to begin than one of my personal favourites—the extraordinary Black Ghost Knifefish.

1.Black Ghost Knifefish (Apteronotus albifrons)

There are very few freshwater fish quite like the Black Ghost Knifefish. Even after you've seen plenty of them, there is something mesmerising about watching one move. Rather than swimming in the conventional way, the fish propels itself by rippling the long fin running beneath its body, allowing it to glide forwards and backwards with remarkable control.

But what makes the Black Ghost even more extraordinary is something we can't see. Native to freshwater systems in tropical South America, it is a weakly electric fish. It generates an electrical field around its body and detects disturbances in that field, helping it navigate and locate objects and prey, particularly in dark or murky conditions.

It is also a wonderful example of why we should never judge the requirements of a specialty fish by the size of the juvenile sitting in an aquarium shop.

At a Glance

• Scientific name: Apteronotus albifrons
• Adult size: Commonly around 40–50 cm in aquariums, with larger specimens possible
• Lifespan: Potentially 10–15 years or more with excellent care
• Aquarium: A very large aquarium for an adult; think in terms of a long-term home of several hundred litres, with plenty of usable floor length rather than simply water volume
• Temperature: Approximately 24–28°C
• pH: Around 6.0–7.5; slightly acidic to neutral conditions are a good target
• Water: Soft to moderately hard, clean and stable
• Diet: Carnivorous/insectivorous; meaty foods such as worms, insect larvae, crustaceans and other appropriate foods
• Temperament: Generally peaceful with suitably sized tankmates, but predatory towards fish small enough to be eaten
• Activity: Primarily nocturnal/crepuscular; generally occupies the lower and middle areas
• Experience level: Intermediate to experienced

Bringing the Black Ghost's Natural World Home

Black Ghost Knifefish occur in South American river systems, including parts of the Amazon and Orinoco basins. They are associated with environments containing submerged roots, woody debris and other structure, and their electrical sensory system helps them negotiate their surroundings and find food when vision is less useful.

That gives us a very good clue about the aquarium we should provide.

A Black Ghost needs security. Driftwood, robust plants, shaded areas and several retreats can create a much more appropriate environment than a brightly lit, sparsely furnished display tank. At the same time, it needs sufficient unobstructed space to move freely—particularly as it grows.

This is one of those occasions where aqua scaping isn't simply about making the aquarium attractive. The plants, wood, rocks and shelters should create a series of secure areas through which the fish can move rather than one isolated cave at the end of an otherwise exposed tank.

“I've Bought This Beautiful Fish and All It Does Is Hide!”

I heard variations of this many times during my years in the pet industry.

Someone buys a beautiful Black Ghost, takes it home, provides a cave or perhaps a hollow aquarium ornament—and then becomes disappointed because the fish promptly moves in and barely seems to come out.

But from the fish's point of view, it is doing exactly what makes sense.

Black Ghosts naturally seek shelter and are much more active under subdued conditions and after the main aquarium lights have dimmed or gone off. If the only place in the aquarium where the fish feels secure is inside a completely enclosed ornament, that is very likely where it will spend much of the day.

One solution I used to suggest was a purpose-made transparent aquarium tube or shelter, positioned amongst dense plants and other cover. Done well, the fish can feel enclosed and protected while its keeper can still quietly observe it through the shelter.

The important part isn't actually the transparent tube—it's the sense of security around it. A clear tube sitting exposed in the middle of a brightly lit aquarium rather defeats the purpose. Surrounding the retreat with plants, driftwood and shaded areas helps create the protected environment the fish is looking for.

And don't improvise with old bottles, random pieces of glass or other household objects. Use materials designed or confirmed as safe for aquarium use, with smooth surfaces and openings large enough for the fish to enter, turn or leave without becoming trapped as it grows.

Lighting: Work With the Fish, Not Against It

Black Ghost Knifefish are a perfect example of why brighter isn't necessarily better.

You can still have a beautifully planted aquarium, but creating shaded areas is important. Floating vegetation, tall plants, driftwood and carefully positioned lighting can provide a mixture of brighter and darker zones.

You may also find that the fish becomes more visible around feeding time, in the evening or as the aquarium transitions into darkness. Rather than trying to make a Black Ghost behave like a daytime community fish, learn its routine.

Over time, some individuals become remarkably accustomed to their keeper and may venture out readily when they associate that person with food. That's part of their appeal—you don't merely look at a Black Ghost; you gradually get to know its behaviour.

What Should a Black Ghost Eat?

This is not a fish I would expect to thrive on a monotonous diet of ordinary tropical flakes.

Black Ghosts naturally feed on small aquatic animals, insect larvae, worms and other animal prey. In captivity, suitable foods can include bloodworms, blackworms or other appropriately sourced worms, brine shrimp, mysis shrimp, chopped prawn and other quality meaty frozen or live foods appropriate to the size of the fish. A good-quality sinking carnivore food can also form part of a varied diet once the fish accepts it.

Because Black Ghosts are naturally more active in low light, when and where you feed can matter almost as much as what you feed. A shy new fish may not compete confidently with fast daytime feeders. Feeding towards dusk, placing food near its normal foraging area and watching to make sure it actually eats can make a considerable difference.

As always with live food, I prefer reputable aquarium sources rather than collecting worms, larvae or other organisms from drains, ponds or waterways where parasites, pollutants or unwanted organisms could be introduced.

Can I Keep a Black Ghost with Neon Tetras?

This is exactly the sort of question that needs more than a simple compatibility chart.

A small juvenile Black Ghost may appear perfectly peaceful in an aquarium containing Neon Tetras and other little community fish. That doesn't make them suitable long-term companions.

The Black Ghost is a predator. As it grows, small fish that can fit into its mouth may become food, particularly when everyone else has settled down for the night and the Black Ghost becomes active.

Suitable companions need to be chosen according to the adult Black Ghost, not the little one you bring home.

Larger peaceful fish can be possibilities where aquarium size, water requirements and temperament are compatible. But very aggressive, highly territorial or persistent fin-nipping species are poor choices, and any potential tankmate needs to be considered individually rather than relying on the vague label “community fish”.

What About Angelfish?

Angelfish are a much more realistic proposition than Neon Tetras, particularly when both species are appropriately sized. Their water requirements can overlap and adult Angelfish aren't usually viewed as easy prey.

However, that doesn't automatically make the combination suitable for every aquarium. An adult Black Ghost requires considerable space, and Angelfish themselves can become territorial, particularly when breeding. The aquarium needs enough room and structure for the fish to avoid one another rather than forcing very different species into constant close contact.

In other words, compatible on paper doesn't always mean compatible in your particular tank.

Can I Keep Two Black Ghost Knifefish Together?

This is another situation where I'd be cautious.

Black Ghost Knifefish use electrical signals not only for navigation and hunting but also in communication, and individuals can be territorial towards their own kind. Keeping multiple Black Ghosts successfully requires considerably more space, shelter and experience than keeping one.

For most home aquarists, I would much rather see one Black Ghost given an exceptional environment than several squeezed together simply because one wasn't enough.

The Tiny Black Ghost in the Shop Won't Stay Tiny

This is perhaps the most important practical consideration with this species.

Juveniles are commonly sold at a size that makes them look perfectly manageable. But you're buying the future adult, not today's juvenile.

An adult Black Ghost is a substantial fish, and its unusual body shape means that simply quoting litres doesn't tell the whole story. It needs enough length and usable space to turn, glide, forage and move between retreats comfortably. Filtration also needs to cope with the waste produced by a large carnivorous fish while maintaining excellent water quality.

This is a fish for which I would plan the adult aquarium before purchasing the juvenile.

If the only answer is, “I'll buy a bigger tank when it gets too big,” I would wait until that bigger tank exists.

Why I Love Them

For all those requirements, I think the Black Ghost Knifefish is one of the most fascinating freshwater aquarium fish you can keep.

Its extraordinary movement, electrical sensory system, nocturnal habits and individual behaviour make it very different from the conventional tropical fish experience. Give it somewhere secure to retreat, subdued areas to explore, suitable food, excellent water quality and enough room to become the fish it is supposed to become, and you have an animal that can be fascinating to observe for many years.

The secret isn't finding a way to stop a Black Ghost from behaving like a Black Ghost.

It's creating an aquarium where it feels secure enough to let you see it doing so.

2. African Butterflyfish (Pantodon buchholzi)

If the Black Ghost Knifefish owns the shadows, the African Butterflyfish owns the surface.

This is another fish that hardly looks real when you first encounter it. Viewed from above, its enormous pectoral fins spread out on either side of its body almost like wings, while its large, upturned mouth gives away exactly where this fish expects its next meal to appear.

The African Butterflyfish comes from slow-moving and still freshwater habitats in West and Central Africa, where it spends much of its life immediately beneath the surface, amongst overhanging vegetation, roots and floating plants. It is an ambush predator, waiting for insects and other small prey to come within striking distance.

And unlike the Black Ghost, which may disappear into the depths of an aquarium, this fish can spend an extraordinary amount of time appearing to do almost nothing at all.

Don't be fooled. It is watching.

At a Glance

• Scientific name: Pantodon buchholzi
• Adult size: Approximately 10–13 cm
• Lifespan: Around 5 years, potentially longer with excellent care
• Aquarium: Around 120 litres or larger is a sensible starting point, but surface area is particularly important
• Temperature: Approximately 24–28°C
• pH: Around 6.0–7.5, preferably slightly acidic to neutral
• Water: Soft to moderately hard; clean, stable water with relatively gentle surface movement
• Diet: Carnivorous/insectivorous; particularly adapted to taking food from the surface
• Temperament: Predatory towards small fish; generally best with peaceful, appropriately sized tankmates that don't constantly compete at the surface
• Activity: Almost entirely associated with the uppermost level of the aquarium
• Experience level: Intermediate

A Fish Designed for the Surface

Everything about an African Butterflyfish tells you where it belongs.

Its body is relatively flat across the top. Its eyes are positioned to watch what is happening above it. Its mouth points upwards. Those spectacular pectoral fins spread across the surface, helping create the strange butterfly-like appearance from which it gets its common name.

Rather than giving this fish a conventional aquarium and expecting it to adapt, think about the top few centimetres of water as its world.

Floating plants and vegetation reaching towards the surface can provide cover and make the fish feel considerably more secure. Open areas should remain so it can feed and move freely, but an aquarium with a completely bare, brightly illuminated surface isn't making the best use of what we know about this species.

Water movement deserves attention too. Good filtration is still essential, but African Butterflyfish generally appreciate relatively calm surface areas rather than being constantly pushed around by a powerful return blasting across the top of the aquarium. Filter flow can often be positioned or diffused so good filtration and oxygenation are maintained without turning the entire surface into a washing machine.

The Lid Is Not Optional

If there is one husbandry point I would underline with this fish, it is this:

African Butterflyfish can jump.

And they don't merely perform the occasional little hop.

In nature, their powerful pectoral region and surface-dwelling lifestyle allow them to launch themselves from the water when pursuing prey or escaping danger. In an aquarium, that same ability can end disastrously.

A secure, well-fitting lid is therefore essential. Check gaps around filter pipes, electrical cables and feeding openings as well. A surprisingly small opening may be all a startled fish needs.

I'd also be careful about how close the water surface sits beneath the lid. Providing an appropriate air space above the water is preferable to having the aquarium filled almost to the glass, particularly with a fish capable of explosive upward movement.

This isn't a fish I'd ever keep in an open-top display aquarium, no matter how beautiful the aquascape might look.

Feeding the Hunter

This is where keeping African Butterflyfish becomes particularly enjoyable because their natural feeding behaviour is so obvious.

They are specialised surface predators and naturally consume insects, insect larvae and other small animals encountered at or near the surface. In captivity, we can use that behaviour rather than expecting them to chase generic food through the water column.

Appropriately sized insects and insect-based foods can be particularly useful, alongside foods such as bloodworms, mosquito larvae, brine shrimp, mysis and other suitable meaty frozen or live foods. Some individuals will accept quality floating prepared foods, but I wouldn't want that to be the entirety of the diet.

If offering live insects, they should come from a safe source. I wouldn't collect insects from somewhere they may have encountered pesticides or other chemicals simply because feeding live prey seems more “natural”. Natural feeding should never mean introducing an unnecessary risk.

Watching an African Butterflyfish feed also makes you appreciate just how deceptive its stillness can be. One moment it appears to be a floating leaf. The next, the food is gone.

“Can I Keep It With My Neon Tetras?”

Here we go again!

The answer I'd give is: I wouldn't choose Neon Tetras as companions for an adult African Butterflyfish.

This is a predator with an unexpectedly large mouth. Small fish that venture close enough to the surface may be regarded as food, and judging compatibility according to the size of a young Butterflyfish in the shop can lead to the same mistake we discussed with the Black Ghost.

An aquarium can look completely peaceful for weeks or months—until one morning somebody notices that the Neon Tetra population appears to be getting smaller.

That's not an aggressive or “naughty” Butterflyfish.

That's a predator doing what predators do.

What Can Live With an African Butterflyfish?

The best companions are generally peaceful fish that are too large to swallow and that predominantly occupy the middle and lower parts of the aquarium.

That separation of swimming levels can work beautifully. The Butterflyfish has its territory at the surface while other species occupy the space below.

However, I'd avoid aggressive or persistent fin-nippers. Those elaborate fins are an obvious target, and a fish that spends much of its time near the surface doesn't have unlimited options for getting away from harassment.

I'd also think carefully before combining it with other dominant surface feeders. Compatibility isn't only about whether fish attack one another. If another species charges around the surface at every feeding, a quieter Butterflyfish may continually lose access to food.

Can I Keep More Than One?

African Butterflyfish can sometimes be kept with others of their species, particularly when there is a generous amount of surface territory, cover and suitable feeding opportunities. But again, surface area matters more than simply looking at the litre capacity printed on the aquarium box.

Two tanks can hold the same volume of water while offering completely different amounts of usable territory to a fish that spends virtually its entire life at the top.

Watch individuals carefully. If one fish continually dominates the best positions or prevents another from feeding comfortably, the arrangement isn't working simply because nobody has visibly injured anybody.

Plants Aren't Just Decoration

This is a lovely species for demonstrating how planting can serve a behavioural purpose.

Floating plants can create patches of shade and broken cover similar to the protected surface areas these fish naturally favour. Tall plants reaching the surface, along with carefully positioned driftwood or roots below, can add to that sense of security.

But don't completely carpet the surface.

The fish still needs clear areas in which to feed and move, and the aquarium still requires adequate gas exchange. Think of it as creating a mosaic of cover and open water, rather than choosing one or the other.

A Very Different Kind of Aquarium Fish

The African Butterflyfish isn't going to spend its day racing from one end of the aquarium to the other displaying itself for you.

Its appeal is subtler than that.

You begin noticing how carefully it positions itself beneath floating vegetation. You see those enormous eyes watching the surface. You learn the spots it prefers. And then you offer food and suddenly see the lightning-fast predator hidden inside that apparently motionless fish.

It is precisely the sort of species that becomes far more interesting once you understand why it behaves the way it does.

And from a fish that has mastered life at the surface, our next specialty fish takes us in a completely different direction—to one that explores its surroundings using an electrical sense and an extraordinary trunk-like appendage:

the Elephantnose Fish (Gnathonemus petersii).

3. Elephantnose Fish (Gnathonemus petersii)

If ever there were a fish that proves just how extraordinary evolution can be, it is the Elephantnose Fish.

Its most obvious feature is the strange, trunk-like projection beneath its mouth, which gives the fish its common name. But this isn't actually a nose. It is an elongated, highly sensitive extension of the lower jaw, which the fish uses to investigate its surroundings and search for food.

And that's only part of the story.

Like the Black Ghost Knifefish, the Elephantnose is a weakly electric fish. It generates a weak electrical field and uses specialised receptors to detect changes within that field, helping it navigate, communicate and locate food. For a fish that naturally spends considerable time in dim, murky water, this remarkable sensory system allows it to perceive a world we cannot see.

They are fascinating fish—but they are also sensitive ones. The Elephantnose is certainly not a species I would recommend buying on impulse.

At a Glance

• Scientific name: Gnathonemus petersii
• Adult size: Approximately 20–25 cm
• Lifespan: Often around 6–10 years, potentially longer under excellent conditions
• Aquarium: Around 200 litres or more for a single adult is a sensible starting point, with generous floor space; considerably larger if attempting a group
• Temperature: Approximately 24–28°C
• pH: Around 6.0–7.5, with slightly acidic to neutral water generally preferred
• Water: Soft to moderately hard; exceptionally clean, stable water is important
• Diet: Primarily carnivorous/insectivorous; worms, insect larvae, small crustaceans and other suitable meaty foods
• Temperament: Generally peaceful towards unrelated suitable tankmates, but relationships with its own species can be complicated
• Activity: Predominantly lower levels; most active in subdued light and after dark
• Experience level: Intermediate to experienced

That “Trunk” Has a Job to Do

One of the biggest mistakes we can make with an unusual fish is admire its strange anatomy without asking why it evolved that way.

The Elephantnose occurs in freshwater habitats of West and Central Africa. In the wild, it spends considerable time searching along the bottom for small invertebrates and other food. Its elongated lower jaw is covered with sensory receptors and is used to probe and investigate the substrate.

That immediately tells us something important about its aquarium.

The bottom of the tank matters.

I would choose a fine, soft sand rather than coarse or sharp gravel. The fish should be able to investigate and forage naturally without repeatedly rubbing that sensitive appendage against rough substrate.

This is also a wonderful fish for creating a more natural-looking aquarium. Smooth driftwood, roots, plants, shaded retreats and areas of open sand can provide both shelter and somewhere to forage.

Rather than creating a perfectly manicured aquascape where everything is arranged for our benefit, leave some areas where the Elephantnose can actually behave like an Elephantnose.

A Fish That Sees Its World With Electricity

The Elephantnose belongs to a remarkable group of African electric fishes known as mormyrids.

It produces electrical pulses using a specialised electric organ. Receptors in its skin detect distortions in the resulting electrical field, providing information about objects, food and other animals around it.

It isn't producing the sort of powerful electrical discharge associated with an electric eel. We're talking about a weak sensory and communication system.

But imagine what that means from the fish's perspective.

An Elephantnose isn't experiencing your aquarium entirely through vision. The wood, rocks, substrate, plants, food and other fish are all part of an electrical sensory landscape as well.

It's one of the reasons I find these fish so fascinating. We're looking through the glass thinking we understand the aquarium because we can see it. Meanwhile, the Elephantnose is gathering information about that same environment in a way completely unavailable to us.

Lighting and Shelter

Bright, exposed conditions are not ideal for an Elephantnose.

Subdued lighting, shaded areas, caves, driftwood and planting can help the fish feel secure enough to explore. You don't necessarily have to keep the entire aquarium dark; thoughtful aqua scaping can create a mixture of light and shade.

Again, the goal isn't to remove hiding places so that we're forced to see the fish.

Give it choices.

A fish that knows it can retreat somewhere safe may actually become much more confident about coming out. Over time, you can also learn its routine and enjoy watching it when it naturally becomes more active rather than trying to change that routine to suit ours.

Feeding Can Be One of the Biggest Challenges

Elephantnose Fish are not the sort of fish I would simply throw a handful of flakes at and assume everyone has eaten.

They naturally search for small animal prey, particularly insect larvae, worms and other invertebrates. In captivity, foods such as bloodworms, blackworms, tubifex from a safe commercial source, mosquito larvae, brine shrimp and other appropriately sized meaty frozen or live foods can form part of a varied diet. Some individuals can also learn to accept suitable prepared sinking foods.

But there is another issue: competition.

Put a shy Elephantnose into an aquarium with a crowd of fast, enthusiastic feeders and the other fish may have eaten dinner before the Elephantnose has finished deciding where dinner is.

This is where observation becomes so important. Feeding after the main lights have dimmed, placing food near the area where the Elephantnose naturally forages and making sure food actually reaches the bottom can all help.

Don't judge successful feeding by whether food disappeared from the aquarium.

Watch the fish eat.

Water Quality Really Matters

Elephantnose Fish have a reputation for being sensitive to deteriorating water conditions, so this isn't a species for an immature or inconsistently maintained aquarium.

A well-established biological filter, stable temperature, low levels of accumulated waste and regular partial water changes are important. Ammonia and nitrite should, of course, remain at zero in a properly functioning established aquarium, with nitrate kept under control through sensible stocking, feeding, plants where appropriate and maintenance.

This is one fish where I'd rather see the keeper testing the water and observing trends than continually adding products in an attempt to chase supposedly perfect numbers.

Stable, clean water is far more valuable than a cupboard full of bottles promising instant solutions.

“Can I Keep an Elephantnose With My Neon Tetras?”

An Elephantnose isn't the same type of predator as our Black Ghost, and peaceful smaller fish aren't automatically viewed as dinner simply because they are small.

But I still wouldn't build an Elephantnose aquarium around tiny, frantic tankmates.

The bigger consideration is creating an environment where the Elephantnose can feed successfully and behave naturally. Peaceful, appropriately sized fish that occupy different areas of the aquarium and won't continually outcompete or harass it are much better choices.

I'd avoid aggressive species, persistent fin-nippers and boisterous feeders that turn every meal into a feeding frenzy.

And once again, water compatibility matters just as much as behavioural compatibility. Two species aren't good tankmates merely because neither one intends to eat the other.

Can I Keep Elephantnose Fish Together?

This is where things become considerably more complicated.

Elephantnose Fish communicate using electrical signals and can develop social hierarchies. Keeping just two can be particularly problematic because one fish may continually dominate the other, leaving the subordinate animal with nowhere to escape.

Experienced keepers sometimes maintain them in appropriately sized groups, but doing so requires a much larger aquarium, numerous retreats, broken lines of sight and careful observation of individual behaviour. This isn't something I'd suggest simply because someone likes the appearance of several Elephantnose swimming together.

For many home aquariums, a single Elephantnose in a carefully planned environment is the more realistic choice.

Can I Keep an Elephantnose With a Black Ghost Knifefish?

Now we're getting to one of those questions someone standing in a specialist aquarium shop might very reasonably ask:

“They're both electric fish, they're both fascinating, and I have a big tank—why not have both?”

This is where I would resist the temptation to create an aquarium containing every weird fish we fall in love with.

Their preferred water conditions can overlap, and in a sufficiently large, carefully structured aquarium the combination may sometimes be attempted by experienced keepers. But both species use weak electrical fields, both tend to favour subdued conditions, both need secure retreats, and both can be relatively shy feeders.

That creates several potential complications rather than one obvious compatibility answer.

For the average home aquarium, I wouldn't put them together simply for the novelty of having two electric fish. I'd choose the species I really wanted and build an exceptional aquarium around that animal's needs.

Later in this article, when we've met all ten fish, we'll look properly at which of our weird and wonderful species might—or might not—belong together.

A Fish That Rewards Observation

The Elephantnose isn't spectacular because of brilliant colours. Its beauty lies in what it does.

Watch one slowly investigate the sand, manoeuvre around a piece of driftwood or search for food with that extraordinary sensory system and you begin to appreciate just how specialised it is.

And that's exactly why it deserves thoughtful care.

Give it soft substrate, clean and stable water, suitable food, subdued areas, plenty of shelter and tankmates that allow it to feed without constant competition, and you have the opportunity to observe an animal whose perception of its environment is completely different from our own.

With an Elephantnose, the more you understand about what the fish is doing, the more fascinating it becomes.

4. Ropefish (Erpetoichthys calabaricus)

From electric fish, let's move to something that can make you wonder whether you're actually looking at a fish at all.

The Ropefish—also known as the Reedfish—is long, slender and snake-like, with a row of small dorsal finlets running along its back rather than the single dorsal fin we normally associate with fish. Watching one weave through plants and around driftwood is quite unlike watching almost anything else in a freshwater aquarium.

Native to parts of West and Central Africa, Ropefish inhabit slow-moving or still waters, including rivers, streams, floodplains and swampy, heavily vegetated areas. They belong to an ancient group of fishes, the bichirs and reedfish, and possess another remarkable adaptation: they can breathe atmospheric air.

That ability helps them survive in naturally oxygen-poor environments—but it also contributes to one of their less convenient talents in captivity.

Ropefish are extraordinarily good escape artists.

At a Glance

• Scientific name: Erpetoichthys calabaricus
• Adult size: Commonly around 30–40 cm in aquariums, although larger individuals are possible
• Lifespan: Around 10–15 years with good care
• Aquarium: Approximately 250 litres or larger as a sensible starting point for adults, with plenty of floor area
• Temperature: Approximately 24–28°C
• pH: Around 6.0–7.5
• Water: Soft to moderately hard; stable, well-maintained conditions
• Diet: Carnivorous; worms, insect larvae, crustaceans and other appropriately sized meaty foods
• Temperament: Generally peaceful, but predatory towards fish small enough to swallow
• Activity: Primarily bottom and lower levels; often more active during subdued light and evening
• Experience level: Intermediate

Bringing a Reed Bed Into the Aquarium

This is another species where understanding the natural habitat immediately changes the way I'd design the tank.

A Ropefish doesn't need a bare aquarium with one ornamental cave sitting in the middle. I'd create something much more interesting: areas of dense planting, driftwood and roots, smooth rocks, shaded retreats and open stretches along the bottom where the fish can move freely.

A soft sand or smooth, fine substrate works beautifully with this type of environment. Plants around wood and rocks can create little passageways and sheltered areas for the Ropefish to explore rather than forcing it to cross large expanses of exposed substrate.

Because these fish are inquisitive and surprisingly adept at squeezing into small spaces, every piece of hardscape should also be positioned securely. We don't want a heavy rock shifting because a Ropefish has decided that the tiny space underneath it looks particularly inviting.

Yes, It Really Can Breathe Air

Ropefish possess paired lungs and periodically rise to the surface to gulp atmospheric air. That's normal behaviour and an adaptation inherited from an extraordinarily ancient lineage of fishes.

It also means they need unobstructed access to the surface and an air space beneath the aquarium lid.

But don't mistake their ability to breathe air for an excuse to tolerate poor water quality. Being able to supplement aquatic respiration with atmospheric oxygen doesn't mean ammonia, nitrite or accumulated waste suddenly cease to matter.

A Ropefish deserves the same clean, stable, well-filtered water we expect for any carefully maintained specialty aquarium.

The Great Escape

If you remember only one practical thing about keeping Ropefish, remember this:

Check the lid. Then check it again.

These fish can exploit gaps around filter pipes, cables and equipment that don't look remotely large enough to us. Their elongated bodies make them remarkably capable of wriggling through openings, and their ability to survive out of water for a period can encourage them to travel farther than you might expect.

An open-top aquarium is simply not appropriate.

The lid should fit securely, and every opening needs to be considered from the perspective of a determined, flexible fish rather than from ours. At the same time, because the Ropefish needs to gulp atmospheric air, there should be an appropriate humid air space between the water and the cover.

What's on the Menu?

Ropefish are carnivorous predators with a strong preference for animal foods.

A varied aquarium diet can include earthworms or other appropriately sourced worms, bloodworms for smaller individuals, insect larvae, mysis, pieces of prawn and other suitable meaty foods. Many will also learn to accept good-quality sinking carnivore foods.

Because Ropefish frequently become more active as lighting diminishes, feeding towards evening can work particularly well.

They're also another species where simply watching food disappear isn't enough. In a mixed aquarium, faster fish may grab much of the meal before a Ropefish gets to it. Delivering sinking foods closer to its normal feeding area can help ensure it receives its share.

And there's no need to routinely feed live feeder fish. Apart from the potential for introducing parasites or disease, a varied diet of safe, appropriate foods can provide what the Ropefish needs without sacrificing another fish to entertain the keeper.

“But It's So Peaceful—Surely It Won't Eat My Smaller Fish?”

This is where peaceful and predatory can exist in the same sentence.

A Ropefish may show little interest in bullying suitably sized tankmates. That doesn't mean a small fish swimming past at night won't be regarded as food.

Small tetras, tiny rasboras, young livebearers and other bite-sized fish are therefore poor choices. Even if the arrangement appears successful while the Ropefish is young, its potential adult size needs to be considered.

The better question isn't:

“Will my Ropefish attack this fish?”

It's:

“Could an adult Ropefish swallow this fish?”

If the answer is yes, I wouldn't rely on friendship to save it.

Choosing Tankmates

Ropefish can work with peaceful to moderately robust fish that are too large to be considered prey and that share compatible water requirements.

Rather than trying to create an aquarium full of bottom-dwelling oddballs, I'd also think about where each species wants to live. A Ropefish needs room along the substrate and plenty of places to explore. Filling every cave, root and bottom territory with competing species can turn what looked like a very large aquarium into a surprisingly crowded one.

Very aggressive fish can intimidate or injure Ropefish, while persistent fin-nippers are also best avoided.

And feeding behaviour matters. A supposedly compatible tankmate that consumes every scrap of food before the Ropefish gets near it isn't actually a very good companion.

One Ropefish—or Several?

Here's where we get a pleasant change from some of our previous specialty fish.

Ropefish can often be kept successfully with others of their own species when the aquarium is sufficiently large and there are plenty of retreats and feeding opportunities. They may even rest together or gather in the same shelter.

That doesn't mean we simply multiply the number of fish without multiplying the resources.

Several adults require considerably more space, additional hiding places, good filtration and enough food reaching every individual. If keeping a group, I'd make the aquarium larger and richer in structure rather than merely adding more Ropefish to the same amount of territory.

Why Is My Ropefish Trying to Squeeze Into Everything?

Because that's what Ropefish do.

They explore.

A narrow opening between pieces of driftwood, a gap beneath a rock, a dense clump of plants or a space behind equipment can apparently be irresistible.

Instead of trying to stop that behaviour, design for it safely. Give the fish tunnels, roots, planted areas and appropriately sized retreats that it can investigate without becoming trapped. Check decorations for narrow internal spaces, sharp edges and openings that may accommodate today's juvenile but become dangerous as the fish grows.

This is another case where a naturalistic aquarium isn't simply prettier—it gives the animal appropriate ways to use its body and explore its environment.

A Fish With One Foot in the Ancient World

There's something wonderfully prehistoric about a Ropefish.

It doesn't have the spectacular colour of many tropical species. Instead, its appeal comes from its shape, movement, behaviour and remarkable biology. Watching that long body thread effortlessly through vegetation and then seeing the fish rise to take a breath from the surface reminds you that freshwater fish have evolved some astonishing solutions to the environments in which they live.

Give a Ropefish plenty of room, natural cover, appropriate food, compatible tankmates and—please—a very secure lid, and it can become one of the most fascinating inhabitants of a specialty aquarium.

And our next fish can take us in another direction again. Rather than something long, secretive and snake-like, I think we should meet an unusual fish that raises a completely different set of questions for its keeper.

5. Clown Loach

(Chromobotia macracanthus)

The Clown Loach may not look quite as bizarre as a Black Ghost, Elephantnose or Ropefish, but I think it absolutely deserves a place in this article because it is one of the classic examples of a fish that is very easy to underestimate when you see a youngster in an aquarium shop.

Those little orange-and-black striped juveniles are incredibly appealing. They're active, inquisitive and often seem to be having a wonderful time tumbling around together. Unfortunately, their small size at the point of sale has also resulted in countless Clown Loaches ending up in aquariums they will eventually outgrow.

This isn't a solitary little “bottom cleaner”. It is a highly social, long-lived fish that can become very large—and keeping it properly means planning for the adult fish from the beginning.

At a Glance

• Scientific name: Chromobotia macracanthus
• Adult size: Commonly 20–30 cm in aquariums, with larger specimens possible
• Lifespan: Potentially 15–20 years or considerably longer
• Aquarium: A large aquarium with substantial length and floor space; adults really belong in tanks of several hundred litres, particularly because they should be kept as a group
• Temperature: Approximately 25–30°C
• pH: Around 6.0–7.5
• Water: Soft to moderately hard; clean, warm, well-oxygenated water
• Diet: Omnivorous, with a strong appetite for animal foods; worms, insect larvae, crustaceans, snails, quality sinking foods and some plant material
• Temperament: Generally peaceful and highly social, although boisterous
• Activity: Primarily bottom and lower levels, but they'll happily explore elsewhere
• Experience level: Intermediate

A Social Fish—Not a Solitary “Cleaner”

One of the first things I'd consider with Clown Loaches is company.

These are social fish. Keeping one alone because you only have enough space for one misses an important part of the animal's natural behaviour. A proper group—generally at least five, with more possible where space allows—gives them the opportunity to establish their social relationships and interact normally.

And interact they certainly do.

Clown Loaches can chase one another, pile together inside shelters, swim in groups and engage in behaviour that can look surprisingly chaotic. They establish social hierarchies, and sometimes their interactions appear far more dramatic than they really are.

This means the calculation isn't simply:

“Is my aquarium big enough for a Clown Loach?”

It's:

“Is my aquarium big enough for a group of adult Clown Loaches?”

That's a very different question.

Bringing Their Natural Habitat Home

Clown Loaches originate from river systems in Indonesia, particularly Sumatra and Borneo, where their environment changes with seasonal water conditions.

For the aquarium, I'd concentrate on what those habitats tell us about the fish rather than attempting to reproduce one particular riverbank exactly.

They appreciate a well-structured environment with smooth driftwood, roots, plants where practical, shaded areas and numerous retreats. A soft sand or smooth fine substrate allows them to forage without continually pushing their sensitive barbels through sharp gravel.

They also need open areas in which the group can move freely.

This is one of those aquariums where I'd try to achieve a balance between structure and space—plenty to investigate and hide amongst without turning the entire bottom into an obstacle course.

“Help! My Clown Loach Is Lying on Its Side!”

This is one of my favourite Clown Loach peculiarities because it can frighten the life out of someone who hasn't seen it before.

Clown Loaches sometimes rest in positions that make them look decidedly dead.

They may lie on their sides, wedge themselves into odd places or pile on top of one another inside a favourite retreat. You glance into the aquarium, see your expensive fish lying motionless on its side and immediately assume disaster.

Then it gets up and swims away.

Knowing the normal behaviour of the species is important because not every strange behaviour is a sign of illness. Of course, a fish lying unusually still alongside other warning signs—rapid breathing, loss of appetite, abnormal colour, lesions or deteriorating water quality—needs investigation. But a healthy Clown Loach having one of its peculiar naps can be perfectly normal.

They can also produce audible clicking sounds, particularly around feeding or social interactions. That's another surprise for someone who assumed fish were silent pets.

What's for Dinner?

Clown Loaches are enthusiastic omnivores, and variety suits them.

A good-quality sinking food can provide a useful staple, supplemented with appropriate frozen or live foods such as bloodworms, brine shrimp, mysis, worms and other small invertebrates. Vegetable foods can also form part of the diet, including suitable blanched vegetables.

And then there are snails.

Clown Loaches are well known for eating aquatic snails, which is one reason people sometimes buy them when a planted aquarium develops a snail population.

I wouldn't.

Buying a potentially 20–30 cm, long-lived, highly social fish because you have too many snails is rather like buying a goat because the lawn needs mowing.

If the aquarium has a snail explosion, look at why. Excess food is often contributing to the population. Address the underlying problem rather than acquiring an animal whose requirements will remain long after the unwanted snails are gone.

Will They Eat My Other Fish?

Clown Loaches aren't generally fish hunters in the way that a Black Ghost or Ropefish can be.

That makes their community options somewhat broader, but their eventual size and boisterous social behaviour still matter. Very tiny, timid fish may not be ideal companions for a group of large, active adult loaches, even if nobody is deliberately trying to eat anybody.

Better tankmates are generally peaceful species capable of coping with the warm water, activity and scale of an adult Clown Loach aquarium.

There's another consideration here too: temperature.

Clown Loaches prefer quite warm tropical water. A fish may look like a suitable companion behaviourally but prefer considerably cooler conditions. Compatibility means finding an overlap in all their requirements—not simply discovering that they don't fight.

“Can I Just Buy One for Now and Add Some Friends Later?”

Technically you could, but it isn't how I'd plan the aquarium.

If you already know this is a social species, I'd rather establish an appropriately sized aquarium and begin with a suitable group. Adding individuals later can alter the existing hierarchy, and there's always the biosecurity issue of introducing new fish to an established collection.

More importantly, “I'll sort that out later” is how many specialty fish end up spending years in temporary arrangements.

Plan for what they need rather than what is convenient today.

Those Little Spines Are Worth Knowing About

Clown Loaches have another feature that's easily overlooked: a sharp, movable spine beneath each eye.

Normally these subocular spines are folded flat and aren't particularly obvious, but the fish can erect them when threatened.

That means a little extra care is required when catching, transporting or handling a Clown Loach. The spines can become tangled in fine nets and can potentially injure the fish—or the person trying to free it.

For a large specimen in particular, I'd use an appropriately sized smooth container rather than chasing it around the aquarium and tangling it in a fine mesh net.

Plants May Need a Sense of Humour

A beautifully planted Clown Loach aquarium is certainly possible, but I'd choose plants and their positioning carefully.

These fish investigate things. They forage. They push into spaces. And large individuals can disturb delicate plants while going about their business.

Robust plants attached to wood or rock, along with well-established rooted plants protected where necessary, can work better than expecting a carefully manicured carpet to remain pristine.

Again, the aquarium should primarily work for the animals living in it.

Don't Let the Juvenile Fool You

Perhaps more than anything else, this is what I'd like people to remember about Clown Loaches.

The little striped fish you see for sale is the beginning of a very long commitment.

Given appropriate conditions, Clown Loaches can live for decades. They grow slowly, which unfortunately makes it easy to convince ourselves that an undersized aquarium is adequate because the fish hasn't outgrown it yet.

But slow growth doesn't make the adult requirements disappear.

Kept properly—in a group, in a large warm aquarium with excellent water quality, natural places to explore and hide, a varied diet and enough room to grow—Clown Loaches can become magnificent, substantial fish with fascinating social behaviour.

Don't buy the little Clown Loach you see today. Plan for the remarkable adult it may become.

6. Bichir — The Living Dinosaur of the Aquarium

A Bichir is the sort of fish that looks as though it has wandered into your aquarium from another geological age.

With its elongated body, armour-like scales and row of individual dorsal finlets running along its back, a Bichir doesn't look much like the conventional tropical fish at all. Its broad head and deliberate movements only add to that prehistoric appearance.

And in evolutionary terms, that impression isn't entirely misplaced. Bichirs belong to the ancient family Polypteridae and possess some extraordinary adaptations—including paired lungs that allow them to breathe atmospheric air.

There are several species of Bichir in the aquarium trade, and this is one occasion where knowing the exact species you're buying really matters. Adult size varies enormously. A smaller species such as the Senegal Bichir (Polypterus senegalus) is a very different proposition from some of the larger Bichirs that can reach well over half a metre.

For this section, I'm going to concentrate primarily on the Senegal Bichir, while also explaining why the label Bichir on an aquarium-shop tank isn't enough information.

At a Glance

• Scientific name: Polypterus senegalus
• Common names: Senegal Bichir, Grey Bichir, Cuvier's Bichir
• Adult size: Commonly around 30–40 cm in captivity
• Lifespan: Often 15–20 years or more with excellent care
• Aquarium: A large aquarium with generous floor dimensions; around 300 litres or more is a sensible long-term starting point for an adult Senegal Bichir
• Temperature: Approximately 24–28°C
• pH: Around 6.5–7.5
• Water: Soft to moderately hard; clean and stable
• Diet: Carnivorous; worms, crustaceans, insect larvae, pieces of prawn and fish, and quality sinking carnivore foods
• Temperament: Generally relatively peaceful towards fish it cannot swallow
• Activity: Predominantly bottom and lower levels; often more active in subdued lighting
• Experience level: Intermediate

First Question: Which Bichir?

This is one of the questions I'd want someone to ask before handing over any money.

Don't simply buy “a Bichir”.

Find out the scientific name.

The various Polypterus species don't all reach the same size, and there are also different geographical forms and captive-bred varieties in the hobby. Some of the larger species require enormous aquariums as adults.

A juvenile Bichir may be a relatively modest little creature in the aquarium shop. That tells you virtually nothing about the space you'll eventually need.

This is where researching the scientific name rather than relying solely on a common name becomes particularly important.

Bringing Its Natural Habitat Home

Senegal Bichirs originate in Africa, where they inhabit freshwater rivers, floodplains, lakes and swampy environments.

For the aquarium, I'd concentrate particularly on the bottom landscape.

A soft sandy substrate works well, combined with smooth driftwood, roots, rocks and generous shelters. Plants can be used to soften the environment and create shaded areas, but I'd leave plenty of open floor space for the fish to move around.

Bichirs aren't delicate little fish weaving between stems. An adult Senegal Bichir is a substantial animal.

I'd therefore make sure rockwork and driftwood are extremely secure and avoid small holes or ornaments into which an inquisitive juvenile can enter but a growing fish may eventually become wedged.

Subdued areas are particularly useful. Like several of the fish we've already met, Bichirs often become much more active as the light fades.

Why Does It Keep Going to the Surface?

Because it needs to breathe.

Bichirs possess paired lungs and regularly rise to gulp atmospheric air. This is completely normal and is one of their most fascinating adaptations.

The aquarium therefore needs clear access to the surface and an appropriate air gap between the water and lid.

And yes, once again I'm going to mention the lid—but for a different reason.

Bichirs can escape.

Their bodies are powerful and surprisingly manoeuvrable, and an inadequately covered opening around plumbing or equipment can become an exit route. A secure cover is essential.

What Does a Bichir Eat?

This is a carnivore, so I'd build its diet around suitable animal-based foods rather than expecting ordinary community flakes to do the job.

Earthworms can be excellent food where they're obtained from a safe, chemical-free source. Depending on the size of the fish, other options include bloodworms, insect larvae, mysis, pieces of plain prawn and other appropriately sized meaty foods. Quality sinking carnivore pellets can also be useful.

I'd vary the diet rather than relying heavily on one food.

And again, live feeder fish aren't necessary. They can introduce parasites and disease, and deliberately feeding live fish isn't required to satisfy the nutritional or behavioural needs of a Bichir.

Because food needs to reach the bottom, watch what happens at feeding time if there are other large fish in the aquarium. A Bichir shouldn't have to compete with a swarm of faster feeders for every meal.

“It Looks Fierce. Is It Aggressive?”

This is where appearances can be deceptive.

Bichirs certainly look predatory—and they are predators—but that doesn't necessarily mean they're aggressive bullies.

A Senegal Bichir may coexist quite peacefully with appropriately sized tankmates while completely ignoring them.

The important phrase there is appropriately sized.

If another fish fits into the Bichir's mouth, the relationship can change considerably, particularly after dark.

So rather than asking whether a Bichir is “friendly”, ask:

What will this aquarium look like when everybody is fully grown?

Medium to large peaceful fish with compatible water requirements can be possibilities. Tiny community fish, fry and small bottom dwellers are another matter.

Can Bichirs Live Together?

Unlike some specialty species, several compatible Bichirs can sometimes be kept together successfully when there is ample space.

But size matters.

I wouldn't mix a very large Bichir with a much smaller individual that could potentially be swallowed, and I'd provide enough floor space, shelters and feeding opportunities that the fish aren't continually competing for the same resources.

This becomes even more important if different Bichir species are being mixed because their eventual sizes can be dramatically different.

Don't Forget the Mouth

There's an interesting trap here.

People sometimes look at the length of two fish and conclude that they're similar enough in size to be compatible.

But predators don't measure their dinner with a ruler.

Body shape matters.

A long, narrow fish may be swallowed by a predator that couldn't possibly consume a much deeper-bodied fish of the same length. That's why I'd judge potential Bichir tankmates by their overall body size and shape—not simply the centimetres written on a care sheet.

A Prehistoric Fish With Modern-Day Requirements

It's easy to describe the Bichir as hardy because its ancestors evolved to cope with challenging environments and because it can breathe atmospheric air.

But “ancient” and “hardy” shouldn't become excuses for poor husbandry.

It still deserves excellent water quality, appropriate food, adequate space, a secure environment and an aquarium designed around its adult size.

And that's really what makes the Bichir such a wonderful specialty fish. You're not keeping it because it's brilliantly coloured or because it performs for you.

You're keeping an animal with an extraordinary body plan, lungs, armour-like scales and a lineage that represents one of the most unusual branches of freshwater fish evolution.

It doesn't just look prehistoric. Watching one makes you appreciate how wonderfully strange fish can be.

7. Freshwater Archerfish (Toxotes spp.)

Few aquarium fish demonstrate their hunting ability quite as spectacularly as an Archerfish.

An insect lands on a leaf or branch above the water. The fish positions itself beneath it, takes aim—and fires a remarkably accurate jet of water from its mouth, knocking the insect from its perch and into the water below.

It's one thing to read about it. It's another to actually watch an Archerfish do it.

Several species occur within the genus Toxotes, including species found in northern Australia and throughout parts of Southeast Asia and the Indo-Pacific. And this is where identification becomes particularly important, because not every Archerfish has exactly the same requirements. Some are strongly associated with estuaries and brackish environments, while others occur well into freshwater.

So if you're considering an Archerfish, don't settle for a shop label that simply says “Archer Fish.” Find out which species it actually is.

At a Glance

• Scientific name: Toxotes spp.
• Adult size: Species dependent; many commonly kept species reach around 20–30 cm, with some growing larger
• Lifespan: Often around 5–10 years or more with good husbandry
• Aquarium: Large, particularly because these are active fish and several species are best kept with others of their kind
• Temperature: Generally around 24–28°C, depending on species
• pH: Commonly neutral to moderately alkaline; exact requirements depend on species and origin
• Water: Fresh or brackish depending on the species—correct identification is essential
• Diet: Predominantly carnivorous/insectivorous; insects, crustaceans and other animal foods
• Temperament: Active and predatory; social behaviour varies with species and group dynamics
• Activity: Upper and middle water levels
• Experience level: Intermediate to experienced

First, Find Out Exactly What You're Buying

This is perhaps more important with Archerfish than with most of the species we've discussed.

The name Archerfish describes a group rather than one single aquarium fish, and different species can occur in environments ranging from freshwater rivers to mangroves and estuaries influenced by saltwater.

That means I wouldn't give somebody a bag containing an Archerfish and casually say, “Keep the pH around seven and you'll be right.”

I'd want to know which Archerfish it is.

The commonly encountered Banded Archerfish (Toxotes jaculatrix), for example, is strongly associated with coastal and estuarine habitats and is commonly maintained in brackish conditions. Other species, including some Australian Archerfish, have different distributions and can occur extensively in freshwater.

This is one occasion where the scientific name on the shop's stock list is far more useful than the picture on the tank.

An Aquarium With Something Above the Water

Here is where an Archerfish aquarium can become really special.

Instead of thinking only about what goes beneath the water, we can consider the space above it.

In the wild, Archerfish hunt around overhanging vegetation, mangrove roots and branches. Their extraordinary ability to shoot insects from leaves only makes sense when we consider that environment.

For an experienced aquarist with an appropriate setup, a paludarium-style arrangement or a tall aquarium with carefully planned space above the water can provide opportunities to encourage some of this natural hunting behaviour.

Imagine branches or aquarium-safe planting extending above the surface, with the fish waiting below.

Now we're no longer simply recreating water chemistry.

We're giving the fish an opportunity to use the behaviour that makes it an Archerfish.

How Does It Actually Shoot?

This is the extraordinary part.

The Archerfish forms a narrow channel using its tongue and the roof of its mouth and forces water through it, producing a concentrated jet. It can compensate remarkably well for the visual distortion created when looking from beneath the water through the air-water boundary.

Experienced fish can strike insects from impressive distances.

Young fish develop their ability with experience, and Archerfish have also attracted scientific interest because of their visual processing, learning and hunting behaviour.

Suddenly that rather attractive silver fish with black markings becomes considerably more interesting.

Feeding an Archerfish Naturally

This is one species where feeding can become genuine behavioural enrichment.

Appropriately sourced insects can allow the fish to use some of its natural hunting abilities. Flies, small crickets and other suitable insects may be offered depending on the size of the fish, alongside foods such as prawns, worms, insect larvae and quality carnivorous prepared foods.

But I'd make the same distinction we've been making throughout this article: natural doesn't mean careless.

Don't spray a fly with insecticide and then feed it to the aquarium. Don't collect insects from an area treated with pesticides. And don't introduce random aquatic animals from local waterways.

Use safe, known food sources.

An Archerfish doesn't need live insects at every meal, either. The aim is dietary variety and opportunities for natural behaviour, not turning feeding time into a circus trick.

Could I Teach Mine to Shoot Food?

Quite possibly—and this can be one of the great pleasures of keeping them.

Food can be positioned above the waterline so that the fish learns to knock it down. Some individuals become remarkably proficient and may quickly associate their keeper with feeding opportunities.

But there's an important distinction here.

We're not making the fish perform because it entertains us. We're providing an opportunity for it to practise a behaviour it has naturally evolved to perform.

That, to me, is enrichment at its best.

What About Other Fish?

Here I'd look less at a generic list of “compatible species” and more at the practical realities of the aquarium.

Archerfish become substantial, active predators. Tiny fish and other animals that can be swallowed shouldn't be considered safe simply because the Archerfish spends much of its time near the surface.

At the other extreme, aggressive tankmates that continually intimidate them aren't appropriate either.

Any companion also needs to tolerate the same water chemistry. That's especially important if you're keeping an Archerfish species under brackish conditions. A freshwater fish isn't magically compatible because it happens to be the right size.

And because Archerfish can be enthusiastic feeders, I'd watch quieter tankmates carefully to make sure everyone is actually getting something to eat.

One Archerfish or a Group?

Archerfish are frequently encountered in groups in nature and can be maintained socially, but group dynamics deserve thought.

A sufficiently large aquarium is essential. In cramped conditions, dominant individuals can continually harass weaker fish, and adding just one or two companions doesn't automatically create a harmonious social group.

If I were planning an Archerfish aquarium, I'd plan the group and the adult aquarium together, rather than buying one fish and gradually adding more whenever I happened to see them for sale.

And with several large, carnivorous fish eating substantial amounts of food, filtration and maintenance need to keep pace with the biological load.

Don't Fill the Aquarium to the Brim

This is one of the rare fish where deliberately leaving substantial space above the water can become part of the aquarium design.

It provides room for overhanging vegetation and feeding opportunities, and helps create something closer to the interface between water and land that plays such an important role in the Archerfish's natural life.

Of course, that brings us to another practical consideration: the aquarium still needs a secure cover. Archerfish can jump, particularly when startled or pursuing food, so an open arrangement needs to be designed extremely carefully. A purpose-built covered paludarium-style setup can be far safer than simply lowering the water in an ordinary open tank.

More Than a Party Trick

It's easy for the Archerfish's ability to shoot water to become the entire story.

But I think that sells the fish short.

The really fascinating part is understanding why it can do it. Its vision, mouth structure, hunting strategy and preferred position in the water all connect back to an environment where food may be sitting not in the water—but above it.

And when an aquarium allows an Archerfish to look upwards, take aim and use that extraordinary natural ability, we're seeing something far more interesting than a trick.

We're watching an animal do precisely what evolution equipped it to do.

8. Glass Catfish (Kryptopterus vitreolus)

There are unusual fish because of the way they behave, and then there are fish that make you look twice simply because you can see through them.

The Glass Catfish is almost transparent. Its backbone and internal structures are visible through its delicate body, while its long barbels project from the head like fine whiskers. When a group hangs almost motionless together amongst plants, catching and reflecting the light, they can look more like little pieces of living glass than fish.

They're considerably smaller than many of the specialty fish we've met so far, but don't mistake small for easy. Glass Catfish can be sensitive, they're strongly social, and they really aren't suited to being purchased as one or two novelty fish for an ordinary mixed aquarium.

At a Glance

• Scientific name: Kryptopterus vitreolus
• Adult size: Approximately 6–8 cm
• Lifespan: Around 5 years, potentially longer with excellent care
• Aquarium: Around 100 litres or more is a sensible starting point for a proper group, with good swimming length
• Temperature: Approximately 24–27°C
• pH: Around 6.0–7.5
• Water: Soft to moderately hard; clean, stable and well oxygenated
• Diet: Omnivorous with a preference for small animal foods; quality fine prepared foods supplemented with small frozen or live foods
• Temperament: Peaceful, shy and social
• Activity: Primarily middle levels
• Social needs: Keep in a group—I'd aim for at least six, preferably more where space allows
• Experience level: Intermediate

Yes, You Really Can See Through It

The transparency isn't the result of selective breeding to produce an aquarium novelty. It's a natural characteristic of the fish.

The species we commonly know today as Kryptopterus vitreolus comes from freshwater systems in Thailand. Interestingly, Glass Catfish in the aquarium trade were historically confused with other Kryptopterus species, which is another reason scientific identification matters when we're researching unusual fish.

Their lack of heavy pigmentation allows much of the body to appear almost completely transparent. You can clearly see the vertebral column running towards the tail, while most of the organs are concentrated towards the front of the body.

It's an extraordinary adaptation—and one that gives us a specialty fish without needing a monster-sized aquarium.

Don't Buy Just One Because It Looks Interesting

This is probably the most important thing to understand about Glass Catfish.

They are schooling fish.

A lone Glass Catfish—or even a pair—isn't really allowing us to see the species as it should be. When kept in an appropriately sized group, they tend to hover and move together, and the whole character of the fish changes.

For me, this is also where the aquarium becomes far more beautiful. Rather than one transparent curiosity tucked behind a plant, you have a shimmering group suspended together in the middle of a planted aquarium.

If the tank has sufficient room, I'd much rather see eight or ten than the bare minimum. As always, though, group size has to be balanced against aquarium capacity and filtration.

A Planted Aquarium Suits Them Beautifully

Glass Catfish give us an opportunity to create a very different habitat from the caves and bottom territories we've been designing for some of our larger oddballs.

They appreciate areas of vegetation and shade, but they also need open mid-water space in which the group can assemble and swim.

Tall plants around the rear and sides, driftwood or roots, and perhaps some floating vegetation to soften very bright overhead lighting can create a lovely environment. Leave the central swimming area relatively open rather than filling every centimetre with plants.

This is a fish I'd particularly enjoy keeping in a natural, densely planted display, because the transparency of the fish against green vegetation can be spectacular without needing artificial decorations or intense lighting.

Why Are Mine Hiding?

With Glass Catfish, hiding can tell us something useful.

Newly introduced fish may understandably be shy while settling in, but Glass Catfish that remain withdrawn can be telling us to look at their environment.

Is the group too small? Is the aquarium extremely bright and exposed? Are larger or boisterous fish intimidating them? Is there enough plant cover? Are the water conditions stable?

Instead of immediately reaching for a bottle of something, I'd first look at the fish's surroundings and social situation.

Once comfortable, a group will often spend considerable time out in the open, hovering together in the water column.

Feeding Something You Can Almost See Through

Despite their delicate appearance, Glass Catfish still need a varied, nutritious diet.

Fine quality flakes or small granules can form part of the diet if accepted, supplemented with appropriately sized frozen or live foods such as daphnia, brine shrimp, mosquito larvae and bloodworms.

Because they feed predominantly through the middle of the water column, food size and movement can make a difference. Very large sinking foods disappearing immediately to the bottom aren't particularly useful to a fish hovering halfway up the aquarium.

Small portions offered where the group naturally feeds work much better.

Their transparency can actually make observing body condition particularly interesting. Don't assume that because a fish is eating something it is receiving enough. Watch the group, particularly quieter individuals, and make sure everybody is participating at feeding time.

Can Glass Catfish Live in a Community Aquarium?

Yes—and this is one of the specialty fish in our article for which the answer can genuinely be yes, provided we choose that community carefully.

Peaceful fish of a similar temperament can make good companions. Small to medium peaceful rasboras, tetras and other non-aggressive tropical species with compatible water requirements may work well.

What I wouldn't do is place these delicate, relatively shy fish amongst large aggressive species or extremely boisterous feeders.

And obviously, I wouldn't combine them with one of our larger predators simply because both species appear on this list.

A full-grown Bichir or Black Ghost isn't going to appreciate the Glass Catfish's remarkable transparency.

It's going to appreciate its size.

“Could I Keep These With Angelfish?”

This one is more nuanced than a straightforward yes or no.

Large Angelfish are predators and may consume surprisingly substantial fish if they can manage them. Adult Glass Catfish aren't as tiny as some community species, but their slender body shape needs to be considered.

I'd be much happier building the Glass Catfish aquarium around peaceful companions of comparable size than trying to decide whether a large Angelfish's mouth is quite big enough to cause trouble.

This is one of those situations where choosing the safest compatible community from the outset is better than waiting to discover whether a particular combination works.

Their Appearance Can Tell You Something

Glass Catfish are naturally transparent, but changes in their appearance can sometimes accompany stress or poor condition.

A fish that becomes unusually pale or whitish, separates from the group, clamps its fins, stops eating or behaves differently deserves attention. Start with the basics: water quality, temperature, recent changes, social conditions and signs of disease or injury.

Because these fish can be sensitive to deteriorating conditions, I wouldn't use them as the first inhabitants of a newly established aquarium. I'd prefer a mature, stable tank whose keeper already understands its normal water parameters and maintenance routine.

Not Every Specialty Fish Has to Be Huge

I particularly wanted the Glass Catfish in this article for that reason.

Specialty fishkeeping isn't necessarily about owning the biggest predator or constructing an enormous aquarium.

Sometimes what makes a fish special is much quieter.

A beautifully planted aquarium containing a healthy school of Glass Catfish can be every bit as fascinating as an aquarium containing one enormous oddball. The pleasure comes from understanding what you're looking at: their transparency, their schooling behaviour and the way they use the environment together.

Sometimes the most extraordinary fish in the aquarium is the one you can barely see.

9. Freshwater Pufferfish — Small Fish, Enormous Personality

Few fish have a face quite like a pufferfish.

Those large, independently moving eyes, the almost beak-like mouth and that peculiar way of manoeuvring through the water give them an expression that seems permanently curious. Many keepers will tell you their puffer appears to recognise them, watches what is happening outside the aquarium and quickly learns exactly who provides dinner.

But “freshwater puffer” isn't one fish, and that's the first thing we need to understand.

Some puffers sold through the aquarium trade are true freshwater species. Others require brackish water as they mature, and confusing one for another can result in completely inappropriate long-term care. Adult size, temperament and social behaviour also vary enormously between species.

For this article, I'd like to concentrate on the Amazon Puffer (Colomesus asellus), a genuinely freshwater South American species, while using it to explain why you should never buy something labelled simply “Freshwater Puffer” without finding out exactly what it is.

At a Glance

• Scientific name: Colomesus asellus
• Common names: Amazon Puffer, South American Puffer
• Adult size: Approximately 10–13 cm
• Lifespan: Commonly around 5–10 years with excellent care
• Aquarium: Around 120 litres or more for a small group, with additional space preferable; active swimming room is important
• Temperature: Approximately 24–28°C
• pH: Around 6.0–7.5
• Water: Freshwater; generally soft to moderately hard, clean and stable
• Diet: Carnivorous, particularly molluscs, crustaceans, worms and other meaty foods
• Temperament: Relatively sociable for a puffer, but still capable of nipping and predatory behaviour
• Activity: Active throughout the aquarium
• Experience level: Intermediate to experienced

Please Find Out Which Puffer You've Actually Bought

This is one fish where a common name on a sales tank simply isn't good enough.

The Amazon Puffer is a true freshwater fish. It doesn't need salt added to its aquarium as it matures.

But that advice cannot simply be transferred to every fish with “puffer” written on its label. Green Spotted Puffers, Figure Eight Puffers and other species encountered in the trade have different environmental requirements, including species that naturally inhabit brackish conditions.

So before thinking about tank size, companions or even food, I'd ask for the scientific name.

That one piece of information can prevent years of inappropriate care.

Give It Somewhere to Explore

Amazon Puffers are active, inquisitive fish, so I'd design their aquarium differently from the dark retreats we've created for some of our previous specialty species.

Plants, driftwood, roots, smooth rocks and other natural structures can create areas to investigate, while plenty of open swimming space allows them to move freely.

Rather than creating one fixed wall of decoration, I'd provide visual breaks and different routes through the aquarium. A thoughtfully planted tank can offer stimulation without restricting movement.

These are fish that notice their surroundings.

That also means an extremely bare aquarium may meet their basic physical requirements while providing very little opportunity to do anything.

Those Teeth Never Stop Being Important

One of the most important aspects of puffer husbandry is sitting right at the front of its face.

Puffers possess fused dental plates—often simply described as a beak—which are adapted for crushing hard prey. Those teeth continue to grow, and inappropriate diets can allow them to become overgrown.

This is why feeding a puffer isn't simply a matter of finding a high-protein pellet.

Foods that require crunching and wearing those teeth naturally are extremely important. Appropriately sized snails can be particularly useful, along with suitable crustaceans and other foods with harder shells. Worms and other meaty foods can provide variety, but soft foods alone don't provide the same dental wear.

It's a lovely example of natural feeding doing more than providing nutrients.

The way an animal eats can be part of its healthcare.

Can I Breed Snails for My Puffer?

Absolutely—and for a dedicated puffer keeper, having a separate snail culture can be extremely useful.

Rather than continually buying snails or taking unknown animals from local waterways, a simple separate aquarium or container can provide a controlled source of appropriately sized snails.

I'd avoid collecting wild snails from ponds, creeks or drains. Apart from possible pollutants, they may carry parasites or other organisms we don't want introduced into the aquarium.

And I'd vary the diet rather than feeding enormous snails occasionally. Smaller appropriately sized prey offered regularly can provide much more useful natural tooth wear.

“My Puffer Watches Me. Does It Actually Know Who I Am?”

This is where pufferfish become particularly endearing.

They are remarkably observant fish and can learn routines very quickly. Many keepers find that their puffers approach when they enter the room, follow movement outside the aquarium or become particularly animated when the person associated with feeding appears.

We need to be careful about assigning human thoughts to a fish, but fish are certainly capable of learning associations, and puffers are widely regarded by aquarists as particularly responsive and inquisitive.

It's one of the reasons they can become such engaging animals to keep.

You're not simply watching the fish.

Quite often, the fish appears to be watching you too.

Can Amazon Puffers Live Together?

Unlike some notoriously territorial puffer species, Amazon Puffers are naturally more social and can be kept in groups when sufficient space is provided.

In fact, I would prefer to consider their social needs rather than automatically keeping one alone simply because it's a puffer.

A group needs plenty of swimming room, environmental complexity and enough feeding opportunities that individuals aren't continually competing. As always, watch the animals rather than assuming a recommendation on paper guarantees harmony.

Individual behaviour still matters.

What About a Community Aquarium?

This is where I would be cautious without automatically saying no.

Amazon Puffers are sometimes maintained with other fish, but fin-nipping is a genuine consideration. Slow-moving species and fish with long, flowing fins would not be my first choice.

Small crustaceans and snails are likely to be regarded as food rather than housemates—which shouldn't come as much of a surprise once you've seen what those teeth are designed to do.

If attempting a mixed aquarium, I'd choose robust, active species with compatible water requirements and carefully monitor behaviour. I'd also have a backup plan rather than assuming everybody will simply learn to get along.

Sometimes the most successful specialty aquarium is one designed primarily around the specialty fish itself.

Don't Make It Puff for Fun

Of course, we can't talk about pufferfish without mentioning the behaviour that gave them their name.

Puffing is a defensive response.

When severely threatened, a puffer can rapidly inflate its body to make itself much more difficult for a predator to swallow. It is extraordinary to see—but it isn't something we should deliberately provoke because we'd like to watch it happen.

Don't chase the fish, frighten it or deliberately make it inflate for a photograph.

Ideally, your puffer should have so little reason to use that emergency defence that you may never see it happen at all.

Be Careful When Moving One

If a puffer ever needs to be transferred, I'd avoid unnecessarily lifting it from the water in a net.

Using a suitable container to move the fish while keeping it submerged can reduce stress and avoids encouraging it to inflate with air. This is particularly important because puffing is a defensive response, not normal handling behaviour.

Plan the move before you start rather than chasing an increasingly frightened fish around the aquarium.

The Fish With the Face You Remember

The Amazon Puffer earns its place amongst our weird and wonderful fish without being enormous, nocturnal or electrically equipped.

Its speciality lies elsewhere.

It is inquisitive, highly adapted to its diet, surprisingly interactive and completely unmistakable. Even feeding becomes part of understanding its biology because those extraordinary teeth tell us something about the prey it evolved to eat.

And perhaps that is why people become so attached to puffers.

There is something about those enormous eyes following you along the aquarium glass that makes it very difficult not to wonder:

Who's actually watching whom?

10. Arowana — The Dragon of the Freshwater Aquarium

If we're going to finish a list of weird and wonderful tropical fish, we may as well finish big.

Very big.

Few freshwater aquarium fish have the presence of an Arowana. Long, powerful and covered in large reflective scales, they glide just beneath the surface with an almost prehistoric elegance. Their upturned mouths and two distinctive barbels give them an unmistakable profile, and it's easy to understand why they're sometimes called dragon fish.

But an Arowana is also a perfect fish with which to finish this article because it embodies almost everything we've been talking about.

This is a fish you plan for before you buy it.

There are several Arowana species, and they don't all have identical requirements—or identical legal status. For Australian fish keepers, species identification is especially important because importation and possession rules can apply to particular species. So before purchasing any Arowana, check exactly which species is being offered and the current regulations that apply where you live.

For our purposes, we'll concentrate primarily on the Silver Arowana (Osteoglossum bicirrhosum), the magnificent South American species most people picture when they think of a large freshwater Arowana.

At a Glance

• Scientific name: Osteoglossum bicirrhosum
• Common name: Silver Arowana
• Adult size: Around 75–90 cm is quite possible, with larger specimens recorded
• Lifespan: Commonly 10–15 years or more with excellent care
• Aquarium: Enormous; an adult requires a purpose-planned aquarium measured in many hundreds of litres, with exceptional length and width
• Temperature: Approximately 24–30°C
• pH: Approximately 6.0–7.5
• Water: Generally soft to moderately hard; excellent, stable water quality
• Diet: Carnivorous; insects, crustaceans, fish and other animal prey in nature
• Temperament: Predatory; individual temperament varies
• Activity: Predominantly surface and upper levels
• Experience level: Experienced

Look Up—This Fish's World Is Above It

The Silver Arowana originates from South American freshwater systems, including the Amazon basin. And if we want to understand this fish, once again we need to look at its anatomy.

That enormous upturned mouth isn't accidental.

Arowanas spend much of their time close to the surface, taking prey from the water and from above it. They are renowned for leaping from the water to capture insects and other small animals from overhanging vegetation.

So although an Arowana aquarium obviously needs enormous swimming space, I'd also think carefully about the surface environment. Avoid cluttering its principal swimming zone. Create a natural-looking setting with appropriate wood and planting without turning the upper aquarium into an obstacle course.

And then there is the lid.

The Fish That Can Leave the Aquarium

An Arowana doesn't merely jump.

It can launch itself.

A frightened or feeding Arowana can clear the surface with extraordinary speed and force, and a large fish hitting an inadequate aquarium cover can injure itself badly—or end up on the floor.

A strong, secure and appropriately designed cover is therefore absolutely essential. With a fish this powerful, simply placing a lightweight glass lid over the aquarium isn't something I'd trust without considering how it is secured and whether the entire setup is suitable for the species.

This is one of those occasions when designing the aquarium around the adult animal becomes particularly important.

“It's Only 15 cm Long. Surely I Don't Need a Huge Tank Yet?”

This is probably the question that has landed more large fish in inappropriate aquariums than almost any other.

Technically, a juvenile doesn't need the same physical space as a 90 cm adult on day one.

But that isn't the question I'd ask.

I'd ask:

Where is this fish going to live when it reaches 60, 70 or 80 centimetres?

An Arowana doesn't just become long. It is a substantial-bodied fish that needs enough width to turn comfortably and enough uninterrupted length to swim normally.

This is why I don't particularly like quoting one magical “minimum tank size” for an adult Arowana. A tall aquarium may contain an impressive number of litres while providing inadequate horizontal swimming room.

Dimensions matter as much as volume.

If the adult aquarium isn't financially or physically realistic—remembering the enormous weight of the aquarium, water, stand and equipment—then I'd admire the Arowana without taking one home.

There is absolutely nothing wrong with saying, “I love that fish, but I can't give it what it needs.”

In fact, that's responsible fishkeeping.

Feeding the Dragon

In nature, Silver Arowanas are opportunistic predators. Fish, crustaceans, insects and other suitable animals can all become prey.

In captivity, I'd aim for a varied diet using high-quality carnivorous foods alongside appropriate fresh or frozen animal foods. Prawns, insects, worms and other suitable foods can provide variety, depending on the size of the fish, and many Arowanas can be conditioned to accept good-quality floating prepared diets.

Because they naturally feed towards the surface, floating foods can also encourage a more appropriate feeding position.

What I wouldn't recommend is building the diet around live feeder fish.

Apart from the disease and parasite risks associated with feeder fish, there's no need to continually release live fish into the aquarium simply because an Arowana is a predator. We can provide excellent nutrition and opportunities for natural feeding behaviour without doing that.

Can Anything Actually Live With an Arowana?

Yes—but now we're playing in the big-fish league.

Anything small enough to be swallowed is an obvious risk. But simply choosing another enormous fish isn't automatically the answer either.

Tankmates need to be considered for temperament, adult size, swimming level, water requirements and the extraordinary amount of space required once several large fish share an aquarium.

Large peaceful or semi-robust species are sometimes maintained with Arowanas in appropriately enormous systems, but I'd never construct a collection by simply choosing several impressive fish and assuming size makes them compatible.

One large fish can require a big aquarium.

Several large fish can require something approaching an indoor aquatic system rather than an ordinary home fish tank.

What About Keeping Two Arowanas?

Possible under specialist conditions doesn't necessarily mean sensible for the average home aquarist.

Arowanas can be territorial towards one another, and aggression between large fish can result in serious injury. Multiple Arowanas are sometimes maintained in very large specialist systems, but this isn't something I'd recommend as a casual extension of keeping one.

If somebody is considering an Arowana community, we're well beyond ordinary tropical fishkeeping. Tank dimensions, group composition, filtration capacity, feeding, behaviour and contingency plans all need serious consideration.

Water Quality on a Very Large Scale

Big fish eat more.

Big fish produce more waste.

It's obvious when written down, but it's remarkably easy to underestimate what that means in practice.

An adult Arowana requires powerful, appropriately sized biological and mechanical filtration, excellent oxygenation and a maintenance routine capable of keeping a huge volume of water consistently clean.

Water changes also become a logistical consideration. Changing 20 or 30 per cent of a small community aquarium is one thing. Doing the same with an enormous specialty aquarium involves substantial quantities of water.

Before buying the fish, I'd therefore think about how the aquarium will actually be maintained. Where will replacement water come from? How will it be conditioned and temperature matched? Where will the old water drain? Can equipment be serviced without dismantling half the aquarium?

Good husbandry becomes much easier when those questions are answered during the design stage rather than after a metre-long aquarium is sitting against the wall.

The Fish You Build the Aquarium Around

Perhaps that's the best way to describe an Arowana.

It's not a fish you add because there's an empty space near the surface.

It's the fish around which you design the aquarium.

The dimensions, cover, filtration, aqua scaping, feeding routine and choice of any companions all need to acknowledge what this animal will eventually become.

And when it's done properly, the result can be magnificent.

Watching an adult Arowana glide slowly beneath the surface, turn effortlessly and rise towards its keeper for food is very different from watching the little silver juvenile that first caught someone's attention in an aquarium shop.

That's why I wanted to finish our ten with this fish.

From the electrical world of the Black Ghost and Elephantnose, to the surface hunting of the African Butterflyfish and Archerfish, the strange resting habits of Clown Loaches, the transparency of Glass Catfish and the enormous personality of a puffer, every fish we've met has asked something different of its keeper.

The Arowana leaves us with perhaps the most important question of all:

Not “Can I afford to buy this fish?” but “Can I afford—in space, time, care and commitment—to give this fish the life it deserves?”

I Want Them All! Can These Fish Live Together?

After reading about ten weird and wonderful fish, it's very tempting to start mentally designing the ultimate specialty aquarium.

A Black Ghost cruising through the shadows. An Archerfish patrolling the surface. A Ropefish winding its way around the driftwood. Perhaps an Elephantnose investigating the sand below.

It sounds wonderful.

But a collection of fascinating fish doesn't necessarily make a compatible aquarium.

Some of the species we've looked at could potentially share an aquarium under the right circumstances. Others would be poor combinations, and some would require such an enormous or specialised setup that keeping them together simply wouldn't make sense.

The important thing is not to choose fish because they look impressive together. Start with the requirements of the animals.

Compatibility Is More Than “Will They Fight?”

When people talk about compatible fish, aggression is often the first thing they consider. But two fish can be completely non-aggressive towards one another and still be unsuitable tankmates.

Before combining specialty species, I'd look at the whole picture:

• Adult size: Will one eventually be capable of swallowing another?
• Water requirements: Do they genuinely thrive at the same temperature, pH, hardness and—particularly with some Archerfish—salinity?
• Swimming level: Are several large fish competing for the same part of the aquarium?
• Feeding: Will a shy nocturnal feeder actually get enough food alongside faster, more assertive species?
• Lighting: Does one fish need subdued conditions while another needs a different environment?
• Territory and shelter: Can every fish retreat without being forced into another animal's space?
• Behaviour: Is one species peaceful but extremely boisterous, while another is easily intimidated?
• Sensory needs: With unusual species such as the Black Ghost and Elephantnose, their electrical sensory systems are another consideration.
• Adult aquarium size: Not the size of the fish today—the size and number of the adults you're planning to keep.

That last point can change everything.

A combination that appears perfectly reasonable when the fish are 8 or 10 centimetres long can become completely unrealistic several years later.

Could Some of Our Ten Live Together?

Potentially, yes.

For example, some of the larger, peaceful species we've discussed may have overlapping temperature and water requirements. A suitably sized Black Ghost might coexist with certain appropriately sized peaceful fish. Ropefish can live successfully with tankmates they cannot swallow. Glass Catfish can make lovely community fish when their companions are peaceful and appropriately sized.

But I wouldn't work backwards from a list of fish I want and then try to make them fit.

I'd choose the main species first, design the aquarium around its natural behaviour and adult requirements, and only then consider which companions genuinely belong there.

That's particularly important with our more specialised fish. An Elephantnose shouldn't have to compete for every mouthful of food because we wanted three other unusual species in the same aquarium. An Amazon Puffer shouldn't be placed with long-finned fish and then blamed for behaving like a puffer. An Archerfish requiring a particular water environment shouldn't be compromised simply so another favourite can join it.

And an Arowana changes the scale of the entire conversation.

Once we're dealing with a fish approaching a metre in length, the aquarium isn't simply a larger version of a community tank. It becomes a substantial system designed around a very large predator.

Sometimes One Extraordinary Species Is Enough

There's also something to be said for resisting the urge to collect everything.

A large, beautifully designed aquarium built around a Black Ghost Knifefish can be far more impressive than a crowded tank containing five different oddities.

An aquarium designed specifically for a group of Clown Loaches can allow us to watch their wonderful social behaviour. A planted aquarium full of Glass Catfish gives us something completely different again. An Archerfish setup with space above the water gives us the opportunity to see a behaviour most aquarium fish could never perform.

The aim isn't to own the greatest number of unusual fish. It's to create an aquarium in which the fish you do own can actually be extraordinary.

Before You Bring One Home

If one of these fish has captured your imagination, that's wonderful. Specialty fish can be some of the most fascinating animals we ever keep.

Just do the research before you buy it.

Find out the scientific name. Check its adult size rather than its current size. Learn where it comes from, what it eats, how it behaves, where it spends its time, whether it needs company and what sort of aquarium will allow it to live naturally. If you're considering tankmates, research them as carefully as you researched the feature fish.

And don't be afraid to decide that a particular species isn't right for you.

Sometimes responsible fishkeeping means walking away from a fish you absolutely love because you can't provide what it will eventually need.

There will always be another fascinating species better suited to the aquarium you can provide.

Final Thoughts

The ten fish we've explored couldn't be more different. Some hunt at the surface, others investigate the bottom. Some navigate using electrical signals, some breathe atmospheric air, one can shoot insects from above the water, and another is so transparent you can almost look straight through it.

But they all have something in common.

The more we understand where a fish comes from and why it behaves the way it does, the better we become at creating an aquarium that works for the fish rather than simply looking attractive to us.

That's what specialty fishkeeping should really be about.

Not collecting something unusual simply because we can.

Understanding it well enough to give it the opportunity to thrive.

© 2026 Majella Gee – Majella's Pet Store. All rights reserved.

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