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

Nototheniidae, the notothens or cod icefishes, is a family of ray-finned fishes, part of the suborder Notothenioidei which is traditionally placed within the order Perciformes. They are largely found in the Southern Ocean.