Trematomus is a genus of marine ray-finned fishes, belonging to the family Nototheniidae, the notothens or cod icefishes.

Trematomus was first described as a genus in 1902 by the Belgian-born British ichthyologist George Albert Boulenger when he described four new species of notothen from specimens collected on the Southern Cross Expedition.

[2] In 1982 Arkady Vladimirovich Balushkin created the new genus Pseudotrematomus, in which he placed all the species in Trematomus other than T. newnesi, but this classification has not been widely accepted.

[5] The generic name Trematomus is made up of trema which means "hole" or "opening" and "tomus" which means "cut", Boulenger explained that the "scapular fenestra being pierced in the scapula instead of between the latter and the coracoid".

[4] Trematomus rockcods are found all around the continent of Antarctica with two species which reach as far north as South Georgia.