Callichthyids are armored catfishes living in South America, and are found in most of its freshwater environments. Some species, particularly of the genus Corydoras, are very well known and are appreciated as aquarium pets worldwide. Most callichthyids are bottom dwellers and eat mainly aquatic invertebrates, especially microcrustaceans and insects, as well as lots of detritus. Some species are so common in some parts of South America, that they are fished commercially as food fishes. They are usually cooked in their bony armor and they are really very tasteful.
This family has approximately 161 species grouped in eight genera (about 7.1% of all Siluriformes). Of these species, approximately 130 belong to Corydoras, the largest siluriform genus. A complete catalogue of species, a list of original literature and a key to genera of callichthyids are available.
The callichthyids inhabit a variety of different habitats in the Neotropical region, from small, swift, oxygen-rich creeks to big rivers and flooded areas, including swampy and muddy habitats where oxygen might be virtually absent. To survive in these habitats, callichthyids perform air-breathing. The air is collected at the water surface and swallowed, since their "accessory respiratory organ" is the intestine, and is eventually expelled through the anus. In this family, however, the air swallowed plays a more important role in the maintenance of the hydrostatic balance than in respiration itself, contributing with about 75% of the necessary air for neutral buoyancy (Gee, 1976; Gee & Graham, 1978). Additionally, unlike the catfishes in the families Loricariidae and Trichomycteridae that practice aerial respiration only in case of hypoxia, the Callichthyidae breathe air continuously under all water conditions.
Also very interesting are the reproductive habits of the callichthyids. Aspidoras, Corydoras and Brochis share with most siluroids the condition of substrate brooding. Eggs are laid on substrates like rocks, logs, or leaves. Callichthys, Megalechis, Lepthoplosternum, Hoplosternum and Dianema, on the other hand, have the interesting behavior of building floating nests composed of foam and vegetal debris. Spawning and caring for the eggs and larvae takes place in these nests (see Burgess, 1987, 1989 for some photos).
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