Catfish
They belong to a superorder called the Ostariophysi, which also includes the Cypriniformes, Characiformes, and Gymnotiformes. Catfish have no scales (and are therefore not kosher).
Catfish are a very diverse group of fish. Most are found in freshwater environments of all kinds, but there are also a couple of Atlantic Ocean species. They range in size and behavior from well over a hundred pound fish eaters, to detritivores (species that eat dead material on the bottom), even to a tiny parasitic species commonly called the candiru (Vandellia cirrhosa).
Catfish

Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Siluriformes