Megalechis is a genus of armored catfish in family Callichthyidae, the group that also contains the familiar Corydoras and Hoplosternum. Known in the hobby as hoplo catfish, the two atlas species - Megalechis picta and M. thoracata - range widely across northern and central South America, with atlas records spanning Bolivia, Brazil, Colombia, French Guiana, Guyana, Peru, Suriname, and Venezuela. They share the callichthyid body plan of overlapping bony plates instead of scales and grow to a modest 4.5–9.5 in, tolerating the low-oxygen, seasonally stagnant swamps and floodplain pools typical of the group.
Like other callichthyids, Megalechis can gulp air at the surface and absorb oxygen through its hindgut, letting it survive in water too poor in dissolved oxygen for most fish - an adaptation that also makes it forgiving for beginner aquarists. It is best known in the hobby for its breeding behavior: males build a bubble nest under floating plants or debris and guard the eggs and fry, a display that has made hoplo catfish a long-standing favorite for aquarists who want to breed a catfish rather than just keep one. Both species are assessed as Least Concern, reflecting their broad range and adaptable habits.