Diagnosis: Haplochromis erutus differs from all other species of Haplochromis, except H. bicolor from Lake Victoria, by a small and rectangular mouth with a short upper jaw that curves downwards halfway its length, in combination with blunt, bicuspid and recurved outer oral teeth and, in lateral part of upper jaw, more stout inner teeth, mostly more distinct in dextral side; it differs from H. bicolor by much larger eyes, 35.4-40.7% of head length vs. 21.4-32.0%, slightly more slender interorbital width, 22.5-26.1% of head length vs. 25.8-34.5%, and slightly shorter snout, 23.2-27.1% of head length vs. 26.5-34.2; it differs further by a shallower supraoccipital crest, dominant males with beige-silver vs. red flanks and piebald colouration seemingly absent in H. erutus, while frequently observed in females of H. bicolor (Ref. 126074). Within Lake Edward system, it shares with H. concilians, H. labiatus, H. eduardianus and H. planus stout jaws and large or more strongly developed lips; it differs from H. labiatus by a shorter snout, 22.4-25.4% of head length vs. 26.5-30.2%, and large vs. lobed lips; from H. eduardianus and H. planus by a shorter upper jaw, 20.9-26.% of head length vs. 27.5-33.8% and 27.6-32.1% respectively; and from H. concilians by large vs. strongly thickened lips, a longer premaxillary pedicel, 21.4-24.0% of head length vs. 16.1-21.6%, and beige-silver vs. silver-blue dominant males (Ref. 126074).

Description: Small species with a relatively slender body; head short and convex, snout short, steep and sloping at 55°-70° and eyes large and almost entering the dorsal outline of head (Ref. 126074). Jaws isognathous and with a rectangular outline and a gentle gape inclination of 20°-35°; maxilla extends to anterior margin of orbit; lower jaw short, stout, deep posteriorly and more shallow anteriorly; upper jaw short and with dentigerous arms that curve gently downwards halfway their lengths, mostly more distinct in dextral part of jaw (Ref. 126074). Lips and oral mucosa large and lateral parts of lower lip expand laterally, hereby accentuating rectangular outline of jaws; opercular breathing valves large; neurocranium slightly compressed anteriorly and with a relatively low and wedge-shaped supraoccipital crest (Ref. 126074). Chest scales small; size transition to flank scales gradual; 20-23 scales on upper lateral line, 9-13 scales on lower lateral line; 5-8 scales between pectoral and pelvic fins; 2-3/7-11 cheek scales (Ref. 126074). Outer teeth large and relatively few in both jaws; neck stout, cylindrical and slightly inclined medially; crowns stout, bicuspid and often slightly abraded; major cusps large, blunt, truncated and recurved; minor cusps stout and blunt; outer teeth of large specimens more than 70 mm standard length with strongly recurved and slightly protracted major cusps and reduced and labially implanted minor cusps; dental arcades rectangular in upper jaw, rounded in lower jaw; dental arcades long, outer teeth closely set with crowns touching each other; outer teeth decrease in size posteriorly in the lower jaw, while all teeth in upper jaw equally large; inner teeth stout, relatively small and tricuspid; in lateral part of upper jaw, inner teeth more densely set, larger, bicuspid to tricuspid and more similar in form to outer teeth; tooth bands slender with 1-2 rows of inner teeth on 1-2 outer tooths widths from outer row; in upper jaw, outer and one inner row remain in posteriormost part; in lower jaw, inner rows narrow gradually posteriorly, only outer ros remains over posterior quarter (Ref. 126074). Lower pharyngeal bone slightly longer than broad and equally deep over entire length; pharyngeal teeth slender, major cusps acute, minor cusps reduced to absent and cusp gaps concave; teeth in posteriormost transversal row stout and with blunt major cusps and distinct, small and horizontally inclined minor cusps; teeth set in 23-26 rows; two median rows set with more stout teeth, no molariform teeth (Ref. 126074). Gill rakers on outer row of first gill arch short, stout, unifid and triangular; no rakers on anteriormost part of ceratobranchial (Ref. 126074). Caudal fin emarginate; dorsal and anal fins reach level between two scales anterior to and one scale posterior to caudal fin base; pelvic fins reach level between first and second anal fin spine; pectoral fins between one scale anterior to anus and first anal fin spine (Ref. 126074).

Colouration: Life colouration of dominant males: body beige-silver, cheeks and ventral half of body whitish; flanks with 3-4 faint vertical stripes; caudal peduncle with faint mid-lateral stripe; nostril, interorbital, lacrimal, supraorbital and vertical preopercular stripes and a nape band present; dorsal fin dusky with anteriorly black and posteriorly red lappets; anal fin yellow with dusky base and two large orange egg spots; caudal fin red with dark base, pectoral fins hyaline and pelvic fins black; posterior part of dorsal fin and dorsal part of caudal fin maculated (Ref. 126074). Life colouration of females and juveniles: body beige-silver, belly and cheeks whitish; flanks with 4-5 faint vertical stripes and a faint midlateral stripe; dorsal fin dusky, pectoral and pelvic fins hyaline, anal and caudal fins yellow and anal fin with two small yellow-orange spots resembling egg-spots (Ref. 126074). Colouration in alcohol: body dorsally brown-yellow and ventrally grey-yellow; flanks of dominant males with 2-5 faint vertical stripes and faint midlateral stripe, while all stripes absent or faint in females; dominant males with nostril, interorbital, lacrimal, supraorbital and vertical preopercular stripes and a nape band; dorsal fin dusky and with dark lappets and weakly maculated posterior part; caudal fin ventrally hyaline-yellow, while dorsally dusky and weakly maculated; pectoral and anal fins hyaline; anal fin with two faint egg-spots in dominant males; pelvic fins black in dominant males and hyaline in females (Ref. 126074).