FISH-EAT­ING CATS

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…

Practical Fishkeeping (UK) - - CONTENTS - WORDS: Steve baker

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.

Wide-mouthed frog

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.

Big gulp

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.

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