Sheatfish is a family of catfish (order Siluriformes), specifically the Silurus glanis, or the wels catfish. There are about 100 living species of silurids. These catfish do not have a spine before their dorsal fin, do not have an adipose fin, and the pelvic fins are either small or absent. The anal fin base is usually very long. The largest species in this family is Silurus glanis, the Wels Catfish.