Tomocichla tuba is a large cichlid. It breeds in fast water and is the most abundant cichlid in the river. Adult females are 9 inches long and adult males are 13 inches long. Males often display a pronounced "nuchal hump", essentially an enlarged forehead.

Breeding tubas readily display their status by the white "mask" on the head. Non-breeders do not have a mask. As well, nonbreeders have a solid black stripe from the base of the pectoral fin to the tip of the caudal fin. In breeders, the stripe becomes broken-up by vertical bars of white or varying degrees of a raspberry red color.