Diagnosis: Large bodied tilapiine cichlid; females and unripe males have a grey/green body and fins with 6-7 dark vertical bars on the flank; ripening males with yellowish chin, and notable bright red/orange margins to the dorsal and caudal fins; fully ripe males are black with a blue sheen on the head, bright red/orange margins to the dorsal and caudal fins and a long, branched whitish or yellow genital tassel (Ref. 118638). The breeding male of Oreochromis variabilis is distinguished from O. niloticus and O. esculentus by the intense orange to scarlet colour of the margin of the dorsal fin and the long, tasselled genital papilla, as well as by the general body colour; the orange dorsal margin is present also in grown females and non-breeding males, though narrower and less brilliant (Ref. 2). Other distinguishing characters are: the tilapia-mark is absent in young longer than 15 mm standard length, whereas in O. esculentus it is conspicuous and with a clear ring up to about 70 mm standard length and may still be detected up to 170 mm; the profile usually has a convexity immediately before the eye; there are usually two rows of scales on the cheek in contrast to usually three in O. esculentus; in half-grown and full-grown fishes there are 4-7 series of teeth in the jaws, 3-5 in O. esculentus; the ratio depth of preorbital to length of head is more than 1/5 in O. variabilis, 1/5 or less in O. esculentus; longer gill-rakers; and whereas O. esculentus does not mount beyond the estuaries, O. variabilis enters rivers from the lake (Ref. 2). Oreochromis variabilis differs from both O. malagarasi and O. upembae, its nearest relatives, in the suppression in most phases of blotches on the flanks, in the body colour of mature males, which is blue-grey to blue-black vs. yellowish in O. upembae, in the shape of the profile, which in O. malagarasi and O. upembae lacks the 'bump' before the eye, a lower modal number of soft dorsal and anal rays, and a higher modal number of vertebrae; Oreochromis upembae also differs from O. variabilis in having usually narrow vertical stripes on the caudal fin (Ref. 2).
Description: Above 140 mm standard length there is no fish with a lower jaw ratio of less than 28% length of head, below this length none more than 31.5%; there is no difference in the length of the lower jaw correlated with sex (Ref. 2). The diameter of eye and the depth of preorbital are approximately equal between 152 and 178 mm standard length, when both are 19.2-22.3% length of head (Ref. 2). It is noticeable that the young are as deep-bodied as the adults and that the length of head shows individual variation at all sizes (Ref. 2). Teeth in 3 series at 50.0-57.5 mm standard length, 4-5 series up to 150 mm standard length, 4-7 series above this length; with slender shafts; outer bicuspid, but in ripe males with the minor cusp reduced or absent, in some mixed with a few tricuspids; inner tricuspid; outer series of upper jaw 56-92, 40-60 in the young (Ref. 2). Gill-rakers on the first arch 2-5 + 0-1 + 17-21; totals 21-27; microbranchiospines present from ca. 70 mm standard length (Ref. 2). Width of lower pharyngeal bone less than its median length, 34.6% length of head at 105 mm standard length, 31.6-33.4% at 150-120 mm standard length, 29.0% at 224 mm standard length; blade 1-1.5 times median length of dentigerous area (Ref. 2). Scales on cheek in 2 series, rarely 1-2 scales of a third row; lateral line series 31-33; 3.5-4.5 from origin of dorsal to lateral line, 4-6 between bases of pectoral and pelvic fins, 7 over top of caudal peduncle above lateral line (Ref. 2). Dorsal with XVI-XVIII spines and 10-12 soft rays; totals 27-29; anal fin with III spines and 9-11 soft rays (Ref. 2). Caudal truncate, not heavily scaled, but minute scales may extend a considerable distance along the rays, especially upper and lower; in large fishes all the rays are scaly to near the posterior margin (Ref. 2). Vertebrae 29-31 (Ref. 2). Genital papilla bifid in males in which the gonad is beginning to develop, growing to a long tassel in ripe males (Ref. 2).
Colouration: Body colour grey-green (Ref. 4967). In the young, transverse bars on the body are very narrow and may be curved and the tilapia-mark is present only up to 15 mm standard length (Ref. 2).