Diagnosis: Haplochromis molossus differs from all other known paedophagous Haplochromis within Lakes Edward and George by its broader oral jaws, 67.0-87.0% of lower jaw length vs. 42.0-72.7%, steeper snout, 45-55° vs. 10-40°, and more gentle gape inclination, 20-30° vs. 40-55° (Ref. 127594). It is similar to H. taurinus and H. gracilifur by its rounded jaws and small lachrymal bones; further distinct from H. taurinus by its smaller eyes, 29.8-33.9% of head length vs. 32.9-40.2%, and from H. gracilifur by its deeper caudal peduncle, 65.5-83.6% of caudal peduncle length vs. 62.9-66.4%, longer premaxillary pedicel, 21.6-25.8% of head length vs. 18.1-21.6%, and higher numbers of infraorbital cheek scales, 3-4 vs. 2, and lower lateral line scales, 9-14 vs. 7-9 (Ref. 127594). In addtion, it has more outer teeth in upper jaw than H. relictidens and fewer than H. paradoxus, 22-34 vs. 16-26 and 36-65, respectively; it is distinct from both by smaller lachrymal bones, 13.3-17.0% of head length vs. 15.8-18.4% and 14.7-21.5%, respectively; further separated from H. relictidens by its broadly rounded lower jaw vs. pointed lower jaw (Ref. 127594). Mature males of H. molossus have green bodies and flanks with 6-8 vertical stripes vs. different colour patterns in all other paedophages (Ref. 127594).

Description: Body relatively slender, head short and concave, snout steeply sloping, 45-55°; jaws long, very wide, broadly rounded, isognathous, and with a gentle gape inclination, 20-30°; maxillae bullate, i.e. posteriorly enlarged and exposed, and reach posteriorly to vertical through anterior margin of pupil; lips and oral mucosa firmly thickened (Ref. 127594). Neurocranium of generalised Haplochromis type; supraoccipital crest high and slightly convex (Ref. 127594). Flank scales ctenoid; chest scales smaller than flank scales, size transition gradual; scales in longitudinal series 30-33, upper lateral line scales 20-22, lower lateral line scales 9-14, scales between dorsal fin and upper lateral line 5-6, scales between upper lateral line and anal fin 8-10, scales between pectoral and pelvic fins 5-7, cheek scales 3-4/7-9 (Ref. 127594). Outer oral teeth small, deeply embedded in oral mucosa, and hidden behind lower lip, which extends dorsally over oral mucosa; necks stout, straight, cylindrical, and with straight implantations; major cusps isocline; minor cusps point straight up; in large specimens of more than 100 mm standard length outer teeth weakly bi- to unicuspid with an intercalation of some weakly tricuspid teeth anteriorly and laterally; anterior in lower jaw major cusps straight to very slightly anteriorly curved, minor cusps implanted slightly labially on necks; outer teeth of small specimens of less than 80 mm standard length unequally bicuspid; in all specimens, posteriormost outer teeth in both jaws very small and tricuspid; all outer teeth closely set; inter-tooth distance of one tooth width; dental arcades slender; 1-2 tooth widths between outer and inner rows; inner teeth small, tricuspid, and irregularly set in 1-2 rows that diminish posteriorly, until only outer row remains; tooth bands short, i.e. posterior thirds of premaxillae bear no teeth (Ref. 127594). Lower pharyngeal bone deep, and 1.0-1.1 times broader than long; pharyngeal teeth slender and bicuspid; major cusps acute and straight, cusp gaps absent to small, and minor cusps small; teeth posteriorly in two median rows stouter; posterior edge of bone wet with 24-28 enlarged teeth with blunt and slightly recurved major cusps and reduced minor cusps (Ref. 127594). Ceratobranchial gill rakers on outer row of first gill arch anteriorly stout, short, unifid, and pointed; posteriorly becoming longer, but still rather short, slightly anvil-shaped, and in some specimens bi- to quadrifid; epibranchial gill rakers stout, short, unifid, and pointed (Ref. 127594). Caudal fin emarginate; dorsal and anal fins reach to just before caudal fin base in females, maximally just exceeding this point in males; pectoral fins extend to genital opening; pelvic fins reach to between genital opening and second spine of anal fin in all specimens (Ref. 127594).

Colouration: Live colour pattern of mature males: flanks, dorsum, snout, and caudal and pectoral fins olive-green; on flanks, 6-8 black-turqoise vertical stripes present; belly and caudal peduncle dark-turquoise; cheeks, opercula, and lower jaw turquoise; anal fin hyaline with a reddish hue over spines, and three small, orange egg spots, i.e. size equal to distance between adjacent fin rays, on straight line; dorsal fin dusky, lappets black, i.e. extensions of membranes between spines; caudal fin maculated, i.e. dotted lines on membranes between fin rays; eyes olive-green and black; mental blotch, lachrymal stripes, and nape band present (Ref. 127594). Live colour pattern of females and juveniles: body with vertical colour-gradient from olive-green dorsally to white ventrally; dorsal part of head bluish, cheeks white, and snout dusky; mental blotch present, nape band and lachrymal stripes faintly visible; lappets of dorsal fin and eyes dark; pectoral fins olive-green, all other fins hyaline-green, and posterior tips of dosral, caudal, and pelvic fins hyaline (Ref. 127594). Colour pattern in alcohol: body brownish, in mature males, flanks with 6-8 vertical stripes, caudal fins maculated, and anal fins bearing three small egg spots on a straight line; pelvic fins hyaline in females and black in males; in all specimens, pectoral fins dusky, lappets of dorsal fin black, and anal fin uniformly hyaline; nostril and interorbital stripes faint and clear mental blotch present; lachrymal stripes clear in males, faint in females, and in all specimens, these continue, over eyes, into faint supraorbital stripes (Ref. 127594).