They may lack the bright colours of many tropical fish, but their unusual shapes, varied patterning, and intriguing behaviour have made catfish one of the most popular groups of tropical aquarium fish worldwide. Widely distributed around the world, these fish may be found in a wide range of habitats; some inhabit fast-flowing rivers and others live in stagnant ponds. More than 2000 different species are already known and new ones are still being discovered. Many types can breathe atmospheric air, and you may notice them darting to the surface before they return to their preferred territory near the aquarium floor. There is a see-through type known as the glass catfish and even an upside-down catfish which makes a curious sight as it swims along, alert to possible predators above the water.
The most distinctive feature of catfish are their sensory barbels near the mouth – these resemble cats’ whiskers, which is how these fish earned their common name. The barbels vary in size, and may be branched or feathery in appearance, depending on the species. Catfish use their barbels to assist them in locating food in murky water or after dark, which is when these fish are usually most active.
Catfish may prove rather shy, especially at first, but smaller species are an attractive addition to any community tank, while some bigger specimens make a spectacular display in a suitably spacious aquarium. A few species, such as the striking red-tailed catfish (Phractocephalus hemiliopterus) from South America, are predatory by nature so are not a good choice for a typical community aquarium. This particular species may grow to over 90cm (3ft) in length, so its size alone makes it unsuitable for the average tank.
Feeding
The feeding behaviour of these fish is interesting to witness. Most catfish have a reputation as scavengers, a characteristic that has endeared them to aquarists because they will sometimes eat the food leftovers of other tank occupants. They do certainly forage for food in the aquarium substrate, but it is important to feed them properly if they are to thrive.
By contrast with the foragers, certain types known as suckermouth catfish have powerful, rasping mouth parts which enable them to browse on algae that grows on rocks. They are also able to use their sucker mouths to anchor themselves in fast-flowing water.
Corydoras catfish
The best-known catfish for home aquaria are members of the Corydoras genus. These are small catfish, rarely growing beyond 10cm (4in) in length, and the pygmy catfish (Corydoras pygmaeus) certainly justifies its title, measuring barely 2.5cm (1in) even when adult.
These fish need a sense of security, so set up retreats and crevices using rockwork in the aquarium. Provide water that is neutral or slightly alkaline. Temperature is less significant but should be within the range of 19-26°C (66-79°F). Proprietary foods suit these catfish well, but they will also eat leftovers from other members of a community tank. All corydoras may prove quite disruptive in a planted aquarium because they tend to burrow into the sandy floor covering. Set the aquarium plants in pots to prevent them from being uprooted.
Females are generally recognizable by their larger size and paler colour. The bronze corydoras (C. aeneus) is one of the easiest species to breed in a home aquarium. Ideally, the tank should have a sandy bottom, and you can stimulate spawning by raising the daytime temperature of the water and then allowing it to drop slightly lower than usual during the night.
Females lay their eggs over plants in small batches of a dozen or so at a time. During the course of several hours, they may lay a total of about 200 eggs. After this, you should move the adult fish to separate quarters, before they can eat the spawn. Hatching takes place about five days later, and the newly hatched fry should be reared on special fry foods at first.
The most free-breeding member of the group is probably the peppered corydoras (C. paleatus), so named because of its brown body markings. It was first bred in Europe in 1878, long before many such tropical species could even be successfully kept alive. Selective breeding has now produced various strains of this fish, even some that are pure white.
Unusual catfish
One of the strangest of all catfish originates from southeast Asia. The glass catfish (Kryptopterus bicirrhis) has long, slender barbels, indicating its active nature. Its body is transparent, revealing its skeleton, but it also has an iridescent quality. These catfish tend to inhabit the mid-water levels and thrive when kept as a small group. In contrast to many other catfish, they are very lively, with their tails almost perpetually sweeping to and fro. A similar glass catfish (Eutropietlus debauwi) also occurs in Africa, although its body is decorated by black stripes running along its length.
Other African catfish that are often available for the aquarium include the Synodontis species, such as the upside-down catfish (S. contractus). Its markings appear to be the wrong way up but serve as effective camouflage. These fish spend much of their time swimming on their backs, grazing on algae on the underside of leaves of aquatic plants, although they also feed on the floor of the aquarium. Take care when catching or transferring these fish because, like other catfish, they have spiny fins, which may become entangled and damaged in a catching net. It may be better to catch the fish by directing them carefully into a bag in the aquarium. Upside-down catfish are good occupants for a community aquarium, but it is unknown for them to breed in such a setting. Some other Synodotis species are less suitable, however, proving too large for the average aquarium because they reach nearly 60cm (2ft) in length.