Abstract
The cichlid fish genus Petrochromis is endemic to Lake Tanganyika. The genus consists of six species: 5 previously known and the present new species, P. macrognathus. This new species is easily distinguished from the other species of Petrochromis by the following characters: more projecting upper jaw, posterior margins of lips just reaching to vertical from anterior orbital rim, shorter pectoral fins (26.0-28.2% in standard length (SL) instead of 30.5-36.0%), strongly pronounced premaxillary ascending process, pronounced concavity of chin region, greater number of vertebrae (33-34 instead of 30-32), many small scales present on bases of dorsal and anal fins, and specimens smaller than about 160 mm SL show distinct 11 to 12 vertical stripes (in larger ones those stripes become obscure and the whole body becomes dark-green or dull yellowish-green). A key is given to the species of Petrochromis.
