See-through fish, fish that swims upside down, fish that walk on land, fish that use electricity to kill, and fish that emit sound are but a few of the attractions to be found in this group of fish.
A common feature among the majority of catfish is their bottom-dwelling habit. Another characteristic, often missed by aquarists keeping just one as a cleaner, is that many species are quite gregarious and delight in being kept in numbers of their own kind. Many are nocturnal by nature, and so their “normal” activities often go unnoticed, unless they can be fooled into coming out earlier in the evening by altering the lighting times of the aquarium.
Catfish’s flat-bottomed bodies allow them to hug the bottom of the river or streambed without being swept away by water currents. Catfish are excellent at locating food among the debris on the aquarium floor; taste cells in the barbels assist in this task, and are particularly useful in muddy water or at night when visibility is poor.
Unlike the majority of other fish, catfish have no scales as such; their skin may be left naked or covered with overlapping bony plates called scutes. They often take in air from the surface, but, unlike the Anabantids, they have no auxiliary breathing organ in the head, and oxygen is extracted from gulped atmospheric air in the hind part of the gut.
Usually omnivorous (and with vigorous appetites), some species are more herbivorous and are sought after by hobbyists as a means of controlling algae. Such species have sucker-like mouths equipped with rasping teeth; in the absence of an algae-covered tank, they require extra green matter in their diet, which can be lettuce, spinach, or even canned peas.
Catfish spawn in several ways: corydoras deposit eggs on any flat surface, the eggs being carried to the site by the female between her pelvic fins. The armored catfish, Callichthys callichthys, builds a bubble nest in which to place the eggs beneath a plant leaf. Others spawn on flat surfaces, in pits dug in the gravel, or inside pipes; still others are mouthbrooders.