Diagnosis: A heavily-built large tilapia species with a wide rounded head; dwarf populations exist in some crater lakes, showing bony 'hunger-form' body shape (Ref. 118638). Females and juveniles with grey bodies and 6 or more vertical bars; males have a bright blue, occasionally white or green, 'mask' across the head; when fully ripe, the underside of most of the body can be black, with the upper surface a conspicuous white to pale blue; genital tassel can be long and branched, pinkish to bright yellow; females and non-territorial males are indistinguishable from Oreochromis karongae (Ref. 118638).

Description: Length of head35.7-38.0% of standard length; lower pharyngeal toothed area with concave sides; median length of bone 1.26-1.36 times its width and 37.6-40.6% length of head; blade 1.6-2.4 times the median length of the toothed area; length of lower jaw 31.4-34.0% length of head; teeth of jaws in 3-5 rows (Ref. 2).

Colouration: Breeding male silvery blue with white and pale blue top of head and dorsum and white dorsal margin (Ref. 2).