The catfish belong to the super-order Ostariophysi, order Siluriformes, and are grouped under 31 families. The principal families covered are as follows:

  • Callichthyidae – Small armoured catfish.
  • Siluridae – Catfish with very long anal fins and small, or absent, dorsal fins.
  • Doradidae – Heavy bodied with a single row of bony plates, every of which bear a spine, running along the centre of every side of the fish.
  • Bagridae – Unarmoured catfish with long barbels. Old World.
  • Pimelodidae – Unarmoured catfish with long barbels. New World.
  • Bunocephalidae – Unarmoured catfish with flat heads.
  • I.oricariidae – Spiny armoured catfish with sucking disc mouths.

Catfish never have scales, but some species are partly or totally covered with bony plates, and also the vast majority have barbels.