Diagnosis: Slender bodied tilapia, characterised by its small eye and slender head profile with terminal mouth (Ref. 118638); further a narrow preorbital bone and scales of nape, dorsum and belly are very small, the transition from flank to belly scales abrupt, along a curve from base of pectoral fin to vent (Ref. 2). The upper profile of the head is nearly horizontal and in specimens larger than 130 mm total length there is a steep rise from the occiput to the dorsal fin; the caudal peduncle is long and dorsal and anal fins do not reach its posterior end when adpressed (Ref. 2). Live territorial males have jet black dorsal fins and are black underneath but are pinkish-red on flank and caudal fin; under stress, such as following capture, the flanks darken and the whole fish appear dark grey, apart from the reddish tailfin; females and non-territorial males grey/silver with pale ventral region (Ref. 118638).

Description: The proportions of the head are characteristic (Ref. 2). The eye is very small, the preorbital bone very narrow, the interorbital space relatively narrow, and the jaws and snout are not enlarged in breeding fishes; in small specimens the nearly horizontal upper profile of the head grades smoothly into the dorsal profile of the trunk, but in the larger fishes of Lake Kitangiri and Lake Singida it rises steeply at the occiput to the origin of the dorsal fin (Ref. 2). The postorbital part of the head occupies a greater percentage of the total head-length than in most species and is usually more than 50% (Ref. 2). The small size of the eye contributes to this unusual balance and the snout is also rather short (Ref. 2). The teeth are in narrow bands; the teeth are very small and specimens with all teeth intact are very rare; many teeth are worn, so that the minor cusp is blunt or absent; some of the teeth in males appear to be true unicuspids, with a single, sharp, brown point; in females teeth of the inner rows are bluntly tricuspid, but in males those of the inmost row are usually unicuspid and the intermediate rows contain bi- and tricuspids (Ref. 2). The gill-rakers of the first arch number 2-4 + 1 + 12-17; they are short and bluntly triangular in males, often expanded to square or spade-shaped in females; no microbranchiospines (Ref. 2). The pharyngeal teeth are very fine and numerous, the toothed area in adults covering less than half the median length of the bone, in the very young about half (Ref. 2). Cycloid scales (Ref. 54846); scales in 2-3, usually 3, rows on the cheek and usually extending on to the preorbital bone; 30-34, usually 31-33, scales in the lateral line series; 5-8 scales between origin of dorsal and lateral line; 6-10 scales between bases of pectoral and pelvic fins; an abrupt transition between the normal scales of the flanks and the much smaller scales of chest and belly; scales of dorsal row smaller than those below them, but no naked area at base of dorsal (Ref. 2, 54840). Dorsal fin with XII-XIV spines and 10-12 soft rays; anal fin with III spines and 8-11 soft rays; soft fins blunt, not reaching vertical from base of caudal, at least in females (Ref. 2). Vertebrae 30-32 (Ref. 2). Genital papilla of male approximately spherical or bluntly conical, pigmented (Ref. 2). The caudal peduncle is longer than deep (Ref. 54840).

Colouration: General body colour of life females orange-silver, light grey dorsally, with seven or more dark grey vertical bands from the dorsum to below the lateral line; caudal and pelvic fins light orange; iridescent patches on the gill-covers and a blue streak on the cheek; throat yellowish orange (Ref. 2). Males have darker head and body and the vertical fins are black, the soft dorsal and anal with white oblique lines (Ref. 2). Preserved specimens have plain cream-coloured caudal fins in both sexes, and in females the anal and pelvics are, like the caudal and dorsal, only faintly dusky; in males the dorsal, anal and pelvics are grey to black, especially at the edges, and there are series of white dots on the soft dorsal (Ref. 2). There is no tilapia-mark even in the smallest specimens (Ref. 2).