HOORAY FOR THE HOPLO
It’s far from a new discovery, but it’s so infrequently available that it might well be. In the eyes of some it’s an ugly grey lump, but to others it’s the coolest cat around.
It’s far from a new discovery, but it’s so infrequently available that it might well be. In the eyes of some it’s an ugly grey lump, but to others it’s the coolest cat around.
THE HOPLO cat is so widespread in the wild that it has at least eight different ‘local’ names: still not quite one for each of the 13 countries it’s found in. If you’re travelling through South America, you’ll hear it called Atipa, Cascadu, Currito, Hassa, Kwi-kwi and a whole heap more, pending where you are.
In the UK, on the rare occasions it appears in stores, it’ll be under the trade name of Hoplo, Grey hoplo, or Brown hoplo. I once even heard it referred to as a ‘Hoppyboi’ by a retailer. Heck, call it what you like. Just don’t call it a Callichthys.
To science, it’s known as Hoplosternum littorale. The Hoplosternum genus is made up of three species — H. littorale, H. magdalenae and H. punctatum — and aside some minor differences they all look pretty similar. The trick to telling them apart, apparently, is to look at the space between the eye and the operculum (gill cover). If there’s not a naked patch between the two points, it’s H. littorale . If there is a naked patch, it’s down to checking the shape of caudal peduncle (base of the tail) to tell them apart. If the peduncle is deep, that’s H. magdalenae. If it’s shallow, it’s H. punctatum. Good luck. To bypass that altogether, if you find yourself trying to identify a species you might have more luck by finding out a catch location.
H. magdalenae hails from Venezuela and the Sinu and Magdalena drainages of Colombia, while H. punctatum is caught out of Panama as well as the Atrato River basin of Colombia. As for H. littorale — it’s almost ubiquitous, found anywhere north of Buenos Aires and east of the Andes. That’s why it’s the likeliest of the three species to turn up in stores.
Sadly, when it does turn up, it tends to be either as by-catch with other fishes, or misidentified as one of the Callichthys species of catfish.
It’s an easy enough mistake to (especially as H. littorale was first described as Callichthys littoralis) but it’s also not so hard to differentiate the two genera apart. Once again, look to the tail. Callichthys all have flat or rounded spade-shaped tails while Hoplosternum have a fork.
The joys of taxonomy
But wait, there’s more. There’s another fish LARPing about under the Hoplo name, and it’s even sold as such. Megalechis thoracata, a delightful gentle giant that’s easy to love, is another representative of this confusingly packaged subfamily of catfish. With a marbled livery and a handsome orange pectoral fin in adult males, there’s a reason that this good looker of the family is the most popular of the lot.
You might even be lucky enough to encounter another cousin: the smaller Lepthoplosternum catfish. With similar looks, the ‘lepties’ are the babies of clan, reaching around 6cm or so.
Only the one species appears in the UK — L. pectorale — but the genus comprises six species in total.
Hoplosternum are the giants of this very large family; long and heavy-set armoured catfish that look a bit like a Corydoras on steroids. This similarity is down to a close relationship, with both Hoplosternum and Corydoras being a part of Callichthiydae family; a rich seam of aquarium favourites from the tiny 3cm-long Pygmy cory to the hulking 25cm+ Hoplosternum. Hoplos inhabit their own subfamily, the Callichthiynae, which they share with all the other ‘not quite’ Hoplos mentioned earlier, plus another genus called Dianema. It’s all a bit of a mess, frankly.
The whole naming situation is especially muddled because, in their past, many of these catfish have all been in the taxanomic blender, either previously described as Hoplosternum or Callichthys. And Callichthys didn’t even start out as Callichthys, instead being initially described as Silurus callichthys.
Taxonomy really is quite a swamp.
In the wild
If their taxonomy is a swamp, at least Hoplosternum could live there. These cats are denizens of the inhospitable, seeking out the stillest, boggiest of waters to live in. So hostile are these environments that Hoplos have had to evolve some hardcore physical apparatus to cope with them.
For one, there’s the air breathing. As well as using the gills, Hoplo cats are able to absorb oxygen through their guts, which they do frequently in their anoxic homes. Air is gulped noisily at the surface to be carried down into a respiratory intestine, where the life sustaining gases can be absorbed at leisure.
Even their blood has evolved for a life in low oxygen, and the fish possess multiple haemoglobin types, one of which works under extreme pH distress (the accumulation of carbon dioxide has a pronounced acidic effect on blood), allowing the blood to carry oxygen even in the harshest of conditions.
The external plating, reminiscent of some Gothic knight’s armour,
does more than protect the flesh from hungry birds. In such a hostile environment, and with such ever-present anaerobic conditions, pathogenic bacteria can flourish and would take advantage of even a light surface wound on an unprotected fish. The thick, overlapping scutes help to ensure that diseases don’t find an easy access point.
Swamp conditions provide abundant swamp food, and that’s exactly what Hoplosternum littorale thrives on. All manner of midges, grubs, worms, and copepods that live assorted in the detritus are gobbled with delight during the wet season, and when water levels recede in the dry months the Hoplos swap their diet out for insects (either aquatic insects, or just unfortunate bugs that get trapped in water).
Love island
The poor oxygen content of their water means that Hoplos are required to spawn at the surface; their young are unable to breathe through their guts until somewhere around a month of age, and so they need to be in the oxygen-rich interface between water and air. In most cases Hoplos aim to keep their eggs wet but also just above the waterline.
To facilitate this, they make a bubblenest at the surface from pieces of vegetation stuck together with an adhesive ‘foam’ generated from the male catfish’s mouth. By gulping air and spitting it back out coated with mucus, and by chopping up the water’s surface with his fins, the male Hoplo can create a thick froth which he makes into a stationary raft. He’ll then use his pectoral fins
And guard he does. Far from meek, the Hoplo is one of the most violent catfish around in protecting his young. Fish, birds, human hands — all will be slashed at and slapped in his efforts to keep his offspring safe
— those of a male are spinier than those of a female, and have a 45° hook at the end — to collect debris to reinforce his nest. A nest can easily measure a foot across and bulges a couple of inches above the water when complete.
Breed and be gone
When it comes to spawning, things remain unconventional. The male doesn’t fertilise the eggs in place, but rather seems to release his sperm into the female’s mouth. She passes this quickly through the gut to release over her own eggs as she lays them in the underside of the nest. Once finished, the male will chase her off, lest she stick around and prey upon the young. She takes it in her stride though, and another female will come along to add more eggs to the throng. A single male may receive three or four females in succession, resulting in a brood size of some 20,000 eggs to guard.
And guard he does. Far from meek, the Hoplo is one of the most violent catfish around in protecting his young. Fish, birds, human hands — all will be slashed at and slapped in his efforts to keep his offspring safe. Not that it lasts, however. In just a couple of days after hatching, all interest is lost and no further attention is given to the juveniles.
In the aquarium
Despite having all the visual appeal of a woodlouse with fins, Hoplo cats are widely sought out by that subculture of the hobby that lives for the ugly and cumbersome. Catfish fans everywhere swoon on sight of a real-deal Hoplosternum.
And why not? For one, they are robust. Anything that has evolved to live in waters as filthy as they have can do well in even a neglected aquarium. I once heard a story of an old breeding facility that had been closed down for weeks, with the pumps, filters, heaters and lights shut down, and when some aquarists visited to purchase some of the old hardware, the only remaining fish were some overlooked doradid catfish and a plump, thriving H. littorale.
Hoplos are subtropical fish that thrive in a lower temperature than classic tropicals, and anywhere between 18-24°C suits them just fine. If you experience a powercut, or just want to save on the electric bill, they’ll be cool with it.
Setting up for them is easy. All they need is plenty of space, given their eventual size of some ten inches. A 180cm tank would be great for full grown adults, though 120cm will be okay for growing them on. If anything, these cats prefer depth to length, so ensure that there’s a good 45cm or more from base of the tank to surface.
If you intend to breed them, factor in somewhere to put the females for a while after the eggs are laid. Remember, post-breeding the males turn nasty, to the point where they’ll come out and savage your fingers if you get too close to a nest.
For decoration, just think swamp: a sandy substrate packed out with leaf litter. Silver sand will do fine, and on top of that you would benefit from a few tangles of wood and some dense planting — Java moss is a particular favourite and will be used for a bubblenest. Throwaway floating plants like duckweed may also end up being ‘nested’. I’d not bother trying to make a pleasing planted layout as it’ll just get shredded. Bad luck, aquascapers. Leave plenty of open space. Unlike many catfish, Hoplos are incredibly day active, and will spend time browsing about at higher levels than you’d expect. Surface visits are regular so ensure a well-fitting lid. This isn’t so much because they might jump out, but rather to keep a layer of warm, moist air trapped at the surface that they can breathe from without giving themselves an internal chill.
As for the fundamentals, things couldn’t be simpler. Slow flow is appreciated, so opt for a big external canister filter with some degree of flow control and keep circulation to a minimum. Feeding is dreamy, as they’ll take almost anything from flakes to the finest live food offerings. Stock up on frozen bloodworm. Mysis, blackworm and the like and just mix things up. Finally, the water chemistry. In the wild it leans towards soft and acidic, with a pH between 5.8 and 7.2 recorded across their natural range, but reportedly they’ll go further than this, especially on the alkaline side of things, and have even been associated with slightly brackish conditions.
And there you have it. A hardcore catfish like a thuggish Corydoras that’ll batter its keeper, breed like a gourami, and breathe like a lungfish. That’s the best pitch I can make for them, because the face is something only a mother, or a devoted catfish aficionado, could love.