Clarias is a genus of air-breathing catfish in the family Clariidae, the walking catfishes, widespread across Africa and much of South and Southeast Asia. The atlas covers 35 species with a broad size range, from around 5.5 in up to a hefty 78.5 in, and country records spanning the Democratic Republic of the Congo, Nigeria, Cameroon, Ghana, Angola, Benin, the Republic of the Congo, and Indonesia — reflecting the genus's split presence on both continents. The defining feature of the genus is an accessory breathing organ, a branched, tree-like structure above the gills that lets these catfish gulp air at the surface and survive in stagnant, oxygen-poor water, or even move overland between pools during rains, which is the origin of the common name walking catfish for several species. The body is elongated and scaleless, with long barbels around the mouth and a broad head.
Clarias is of major importance well beyond the aquarium hobby: Clarias gariepinus, the African sharptooth catfish, is one of the most widely farmed freshwater fish in Africa, and has been introduced for aquaculture elsewhere, sometimes becoming invasive. Clarias batrachus, the walking catfish, is similarly significant as both a food fish in Asia and a notorious invasive species where released or escaped. Hobbyist interest is limited mostly to juveniles, since virtually every species grows too large for a typical home aquarium. Conservation is generally favorable for the widespread species but more serious for range-restricted ones: the atlas records a Critically Endangered pair alongside mostly secure, Least Concern species, spanning both adaptable generalists and narrow-range specialists such as Clarias cavernicola, the cave catfish.