So you think catfish are peaceful, laid-back, contented souls who spend their lives shoaling amiably around the bottom of your tank? Think again. Here come the killer cats…
Not all catfish are peaceful, contented, sweet little souls. Some, literally, are killer cats…
There are many different reasons for getting into fishkeeping and many different tastes to cater for. If you’re in it primarily to watch and enjoy pleasant, colourful and active little fish, then these next few pages might make you feel slightly nauseous.
But if you’re into fishkeeping for cryptic, camouflaged oddities, then read on. and if you’re into it for cold-blooded, targeted killers, then you’re going to love some of the monsters on these pages…
We’re focusing on catfish here, and not the easy to care for shoaling species, but the ones that lie in wait, chase down or ambush live fish in their natural habitat – the mean guys.
as an animal that sits at the top of the food chain, humans have always been interested in fellow predators. Our interest was first documented in ancient cave paintings; more recently it’s spawned countless documentaries, books and top trump card games on sharks, bears, wolves, big cats, crocodiles and co. So, it makes perfect sense that some aquarists are head over heels about aquatic predators, even though we don’t see many outline drawings of tooth-wielding fish adorning the walls of our homes.
a common mistake is to instantly think big. Classically, the predatory catfish that shoot to mind are hardto-handle big boys, like the redtailed cats and the Tiger shovelnose, but there are plenty of smaller, very capable predators in the world of wet cats that can be kept in sensibly sized aquaria.
Whale of a time
To begin, here’s one that has a devastating effect on its prey. With the common name of Blue whale catfish, you might expect something that would take a juggernaut to lift, but that’s far from the case. Cetopsis coecutiens actually tops out at 26cm, but that’s not to say you don’t need a good-sized tank. It’s a fish that spends its time in deep, dark water in the large rivers of northern South america where it’s constantly swimming into strong currents and occasionally taking a bite out of any
hapless large fish that comes along.
Nope, they’re not looking for bite-sized Characins down there; they’re looking to tear a chunk of flesh from the flanks of larger, stronger fish that swim through the main channel – even other predatory catfish such as the larger Pimelodids.
When they’re younger, Blue whale catfish shoal. Large shoals have been known to consume most of a big fish carcass in a time that would rival a pack of voracious Piranha – just look at videos of them feeding on the internet. They’re able to bite with a serious set of gnashers, before twisting to tear the flesh like an alligator. When you see several specimens feeding on a fish, it looks like they’re boring their way straight through.
As Cetopsis coecutiens mature, it’s uncertain whether they continue to shoal or become solitary in the wild. In aquaria, they must be the only species kept in the tank as they will eat fish smaller than themselves without hesitation. Anything of similar or greater size will likely be bitten (and not just a little nip…), but they are far less likely to turn on one of their own species.
One essential element of keeping Blue whale catfish is flow – they like lots of it. They also need high levels of dissolved oxygen, which goes hand in hand with the flow. Now I’m not talking about pointing a standard external filter flow into the middle of the aquarium. I’m talking serious flow, like turning your tank over 10 times an hour so they can constantly swim into it, to support them. Specimens in tanks with inadequate movement plummet to lie on the base of the aquarium and gasp heavily to pass water over their gills. These cats don’t want to hunker down in caves or dark tunnels. An ideal set-up would be a large, open tank with dim lighting and that all-important flow.
If one catfish can be the opposite of another, then the Frogmouth catfish is the opposite of the Blue whale cat. The Frogmouth, or Chaca chaca, lives in small habitats of slowmoving to still waters of southern Asia, including sluggish rivers, canals, ponds and peat swamps. Here it sits on the bottom, in among a layer of leaf litter, where it goes unseen by its prey. The Frogmouth’s winning formula is its combination of camouflage, a cavernous mouth and simply staying put.
The lifestyle of Chaca chaca is so sedentary that it can even be touched gently and you’ll see no movement from it. It’s well known for causing injuries in its native lands when accidentally stepped on – in fact, the Frogmouth is considered poisonous by the local people. Maybe there’s some kind of chemical reaction or mechanism at play here – it would make sense of such an inactive fish, but no evidence has been put forward to support this.
Chaca chaca is known to acidify aquarium water somewhat more quickly than other similar fish. Messy, predatory fish can deplete carbonate hardness far faster than most omnivorous fish, due to the amount of high-protein waste produced. The bacterial action needed to deal with such an amount
of waste has the by-product of reducing buffering capacity (and oxygen levels) and down goes the ph. All quite normal, but tanks that house C. Chaca experience a quicker decline in ph than others. One theory suggests that fish which swallow their prey whole, as the Frogmouth does, need stronger digestive juices to break the food down, and it’s been suggested an excess of these acids could have a direct effect on the Frogmouth’s environment. However it occurs, the answer to avoiding dangerously low ph levels is water changing and filter cleaning. I would suggest changing 40-50% of the tank water weekly, along with a filter clean as a minimum, and ideally two 40% water changes per week.
Some people may know C. chaca as the Angler catfish – a less popular common name given to it after seeing movement in the short barbels either side of its mouth. As the moniker suggests, the Frogmouth can move these barbels to imitate small worms or insect larvae among the leaf litter – luring prey towards its vast mouth just as the Angler fish does.
It’s at this point that the Frogmouth moves, and it moves with lightning speed, lunging at its prey while a vacuum is created in its vast mouth. Once its mouth is opened, water floods in, bringing an unsuspecting fish with it – ambush complete.
Talking of vast mouths, the Gulper cat, Asterophysus batrachus, takes this to another level. It leads a similar lifestyle to the Frogmouth cat in slow-flowing, blackwater streams, and uses submerged wooden structures and leaf litter for cover.
It’s a rather ungainly looking beast before feeding, with a large, salmon-like lower jaw that doesn’t meet the top jaw very well. Breathing looks to be a struggle, because the mouth doesn’t close efficiently. Normally, the mouth helps to form the branchial pump (a combined movement of the gill covers and mouth to form a vacuum that passes water over the gills), but this fish has extra skin
membranes inside its mouth instead.
After it has fed, it can look in even more trouble as meals can be very large – even fish of twice its size can be tackled and find their way into the Gulper’s expandable stomach. Then it looks like a bloated fish struggling to breath or swim – a sorry looking sight but, in reality, the fish is happy and well fed.
There are countless videos on the internet of A. batrachus consuming live fish (illegal for the most part in the UK, but allowed in the US, Asia and some other countries) and they look awkward – nuzzling and mouthing their prey and following it around before slowly placing their mouth over the prey’s head.
Some of the videos out there show a quick movement – a snap of the head to catch a fish by its side – but on the whole, it doesn’t look like an effective strategy. If they weren’t in a tank, you’d think the prey would easily be able to get away. Maybe the stained water of their Brazilian and Venezuelan habitats is key, giving them a ‘cloak’ to hunt over.
The Gulper cat also shows a preference to hunt in shallower waters, and anyone who regularly nets fish will know it’s so much easier to do that in the shallows.
In the aquarium, the only tankmates that will be safe are those more than twice the size of the Gulper, and with the cat reaching a maximum size of 25cm, that means tankmates must be the best part of 60cm in length. That’s a big tank. Without tankmates, the Gulper cafish will need a tank of at least 400 litres, and more than one specimen can be kept together.
Feeding is easy, with pieces of fish, prawns, earthworms and similar foods, which may need waving in tongs initially until the Gulper learns to instantly recognise them as food.
With gorge feeders like these, meals don’t need to be so frequent. Younger specimens can be fed several times a week, but slow this down as they grow; mature fish will only require one big meal per week.
One theory suggests that fish which swallow their prey whole, as the Frogmouth does, need stronger digestive juices to break the food down
On the menu
Feeding predatory fish always poses some risk to the aquarist, so it’s advisable to keep your hands out of the tank as much as possible (also avoiding contamination). In the early days of keeping these catfish, they may be stubborn to feed or just not recognise food items. Using tongs or long tweezers can be useful – not only keeping your hands safe, but also allowing you to add movement to an inanimate item of food, which adds interest for the intended diner. If little or no interest is shown, don’t be scared to leave them hungry for a few days to build up their appetite.
Live river shrimp can be fed in the UK, and ideally these should be gut-loaded before feeding. Gutloading simply means feeding the shrimp with a quality food within an hour of feeding them to your fish. This adds to the shrimp’s nutritional value, but beware that feeding live shrimp too often may spoil your fish and put them off static food.
When it comes to fish, there are good meats and bad meats. Thiamine is important to assist an active metabolism, but thiaminase is an enzyme that breaks down thiamine, rendering it useless. It’s destroyed by cooking, but so are certain nutrients, so it’s best practice to feed raw meats that don’t contain thiaminase. These include Perch-like fish such as Tilapia, salmonids like Brown and Rainbow Trout, Common smelt, Cod, Haddock, Pollock, Mackerel and more. Ones to avoid are cyprinids like Carp, Roach and Rudd, catfish, Tuna, Herring and Sardine. Often shellfish, such as mussels, prawns, shrimp and scallops contain the enzyme too. Irregular feeding of these items is fine, but the bulk of the diet should be free from thiaminase.
FAR Left: Frogmouth catfish.
Living in deep, dark waters, the Blue whale catfish’s eyes have receded.
It’s easy to see why the Frogmouth can be accidentally stood on in the wild.
A fish that bores into its dinner.