A love for catfish

Some catfish keepers pine for saddle-snouted Scleromystax that snuffle across the substrate and unceremoniously sideswipe each other. Others prefer bulging Brochis that sit there winking between slapdash bursts to the surface to gulp air.

However, a little deeper in the Callichthyidae world are more subtle prizes. They are the small fish — the ones usually hidden away in dealers’ tanks.

These lack intense colours or the brazen behaviour of their chunkier kin, yet have special appeal. They are the dwarf Corydoras — and of the true dwarf cats three are readily available: Gastrodermus pygmaeus, G. hastatus and Hoplisoma habrosum (pictured above).

There are more small catfish with Hoplisoma cochui and Hoplisoma multimaculatum being equally diminutive. However, these are so rare in the trade that it’s scarcely worth me encouraging real world aquarists to seek them out.

Also, there are the eternally cute Aspidoras cats which differ from other 'Corydoras' in head and fin structure. Aspidoras are more frequently imported so you may see them in shops more regularly now. These fish tend to command a steeper price than their cousins and shoals may be unrealistic for the average hobbyist.

Yet there’s more than financial consideration when opting for these dwarf bottom feeders. There’s also the way in which these cats differ from their kin.

True to their feline namesakes, many corys settle into life in the aquarium well. Cory catfish often spend time nestling and doing nothing, awaiting their next meal and gradually getting podgy.

However, dwarf catfish tend to steer clear of this hedonistic path, clinging to their shoaling roots. They often behave as though their enclosed home was no different from their Amazonian habitats.

Then there’s the interaction they have with other species. G. hastatus, in particular (pictured above) is well noted for its commensalism involving species of similarly marked tetra.

Creating a display for a group of hastatus to shoal alongside these tetras is something of a holy grail for those in the know. The reed tetra, Hyphessobrycon elachys, is becoming a more common sight in fish shops and is a great option.

How do I keep these small catfish?

The ideal fish tank for these Corydoras catfish would feature a soft sandy substrate, a handful of leaf litter and subdued light. The addition of some grassy plants and long strangled stems would add some cover for these diminutive catfish.

H. habrosum, for example, often lives in periodic wetlands, large floodplains to where other fish seasonally migrate. However, it remains behind, suffering from spats of dying off during dry seasons and abundance during the wet. With so much cover, the fish can roam moderately freely, providing that they don’t venture too far. A typical habrosum habitat is above (picture by Hans-Georg Evers).

Neighbours for wild habrosus are an unusual mix, many of which we may not expect to find together. Discarding what we usually think of as a South American community tank, H. habrosum are found alongside fish as diverse as guppies, Characidium, Leporinus and even Rachovia maculipinnis killifish.

Tetras also live with them, as do other catfish including Osteogaster aeneus and C. septentrionalis. Wild predators for those foolish enough to venture into the open include Hoplias wolf fish and Pygocentrus caribe piranha.

Related article: 4 unusual catfish suitable for a community aquarium

What are some suitable tank mates for dwarf corydoras?

For all three of these species, suitable tank mates would be those found in a typical slow moving river or pool in South America. Think shallow-bodied tetras, peaceful suckermouths like Otocinclus affinis, other Corydoras and surface-dwelling hatchetfish.

You should avoid keeping any fish that could fit a dwarf cory into its mouth. These catfish have defensive locking spines on their fins, that could end up killing both predator and prey.

Planting should be heavy, with a mix of broad leafed and grassy greenery. To get good plant growth you may require extra lighting. The pygmies will prefer this to an open, dimmed aquarium where they may feel exposed and threatened.

Shoreline inhabitors, like G. hastatus and G. pygmaeus, are often live in regions withsedges and grasses in abundance.

As with all Corydoras, pay attention to choice of substrate — going for softer, sand-themed bases. Avoid sharp sands and don’t be afraid to add a generous layer of leaf litter. The pygmies won’t spend too much time among it, but seem content from knowing that it’s there.

These fish tolerate temperatures between 22-26°C (72-79°F) with 24-25°C (75-77°F) optimal. The fish will enjoy soft, acidic water, with a pH value of between 6.0 and 7.2 pH, and a hardness below 15°DH.

Related article: The Cordyoras have new names!

Corydoras tetra: Who's mimicking who?

The role of G. hastatus in emulating the markings and swimming behaviour of certain, similarly marked tetras in the wild interests many enthusiasts.

Shoaling is advantageous to fishes, especially from a predation perspective, and the motto is usually ‘the more the merrier.’ As well as shoaling among their own kind, G. hastatus will often school alongside one of a few varieties of tetras.

Several species share the markings of G. hastatus, but some are better suited to co-habit than others.

My favourite contender for a suitable tank mate is Hyphessobrycon elachys (pictured above). Many aquarists have success with keeping these two together.

Serrapinnus kriegi is a similarly marked fish, but has a short temper. I have found that they can turn on the catfish after a few days. Shifting their usually insular and gregarious behaviour towards these new and unwitting shoal members.

Size of tank was not a factor. I saw this hostility both in a 60x30x30cm (24x12x12”) aquarium, as well as a 100x100x100cm (40x40x40”) cube.

Other possibles are the rarely seen Gnathocharax steindachneri, the more common Aphyocharax nattereri (above). Although they may be no better than kreigi in curtailing their hostile tendencies.

Three of the best catfish

My favoured dwarf cats — pygmaeus (pictured above) hastatus and habrosum — are dwarfs by any standard. The largest barely reaches 3.5cm (1.4”) and all could easily hide in the shadows of tetras.

Their size lends them to smaller aquaria, but don’t go to extremes with how tiny a home you can get away with. All too often people recommend them for the dinkiest of nano tanks. However, this can be detrimental to their natural behaviours. It also restricts the quantities you can have and, being obligate shoalers, they need lots of company.

Popular literature cites numbers of five or more as constituting a shoal, but, in many cases, this is woefully inadequate and shows our total lack of understanding about what a shoal actually is.

I wouldn’t consider anything under 8 of any one species, although in practice I’d be inclined to keep these fish in groups of twenties or thirties. Even this would not rival the teeming herds of catfish as seen in the wild.

In the larger aquarium these fish will flock nicely together, although H. habrosum less so than the others. Unusually for a Corydoras, these fish spend much of their time in midwater rather than sat on the base of the tank. In fact, especially in the case of G. pygmaeus, broad leaves of plants, well away from the substrate, would seem the preferred resting spot.

Peak activity for these species is during the twilight hours of dawn and dusk when they actually start to lose some shoaling behaviour — in contrast to other Corydoras which enhance theirs at this time — and move higher into the water column to feed.

A keeper who uses light well to exploit this activity will see the best of these fish.

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