The fish of the genus Petrotilapia, contain the largest mbuna in Lake Malawi. The fish have mainly tricuspid teeth, that they use to comb through the aufwuchs, pulling off diatomous algae, microorganisms, and loose particles. Plankton is also eaten by Petrotilapia. Territorial males will protect are area that varies between 7 to 20 meters squared against conspecifics, though heterospecifics are mostly ignored.
Males are light blue, with a horizontal dark line in the dorsal fin, and orange in the pelvic fins. Females are grey to brown, with a pattern consisting of two horizontal rows of blotches.