Diagnosis: Haplochromis gracilifur differs from all other known paedophages from Lake Edward by its shorter premaxillary pedicel, 18.1-21.6% of head length vs. 21.6-29.1%, smaller number of lower lateral line scales, 7-9 vs. 9-15, exceptionally 7, and bicuspid outer teeth with long minor cusps (Ref. 127594). It resembles H. molossus and H. taurinus by its rounded jaws and small lachrymal bones; it differs from both by its more slender body, 30.2-34.8% of standard length vs. 33.5-38.6% and 33.9-40.1%, respectively; it is further distinct from H. taurinus by its shorter lower jaws, 42.4-44.7% of head length vs. 44.5-51.3%, and smaller eyes, 29.0-32.3% of head length vs. 32.9-40.2%; from H. molossus by its more slender jaws, 61.9-69.4% of lower jaw length vs. 67.0-87.0%, steeper gape inclination, 40-50° vs. 20-30°, and more gentle snout inclination, 10-20° vs. 45-55° (Ref. 127594). In addition, it has more outer teeth in upper jaw than H. relictidens and fewer than H. paradoxus, 26-35 vs. 16-26 and 36-65, respectively; clearly distinct from both by its smaller lachrymal bones, 13.7-14.3% of head length vs. 15.8-18.4% and 14.7-21.5%, respectively; further separated from H. relictidens by lower jaws rounded, whereas pointed in latter (Ref. 127594). Males of H. gracilifur have bright red flanks with two horizontal stripes vs. different colour patterns in all other paedophages (Ref. 127594).

Description: Body very slender, caudal peduncle slim, and anal fin base short; head concave above eyes, snout and premaxillary pedicel short and slope very gently, 10-20°, and dorsal part of head steep, 40-50°; oral jaws long, rounded, and isognathous; maxillae bullate, i.e. posteriorly enlarged and exposed, and reach posteriorly to vertical through anterior edge of eyes; oral mucosa and lips firmly thickened (Ref. 127594). Neurocranium of generalised Haplochromis type; supraoccipital crest high and slightly convex (Ref. 127594). Lower lateral line scales few; flank scales ctenoid; chest scales smaller than flank scales, size transition gradual; scales in longitudinal series 31-33, upper lateral line scales 21-22, loser lateral line scales 7-9, scales between dorsal fin and upper lateral line 6-7, scales between upper lateral line and anal fin 10, scales between pectoral and pelvic fins 5-6, cheek scales 2/7-8 (Ref. 127594). Outer oral teeth very small, deeply embedded in oral mucosa, and hidden behind lower lip, which extends over oral mucosa; necks slender, slightly recurved, with a circular cross section, and gradually expanding into the broader crowns; crowns slightly laterally compressed and bicuspid; posteriormost outer teeth in both jaws tricuspid; crowns of small specimens less than 70 mm standard length with distinct cusp gaps, major cusps strongly truncated and blunt, and minor cusps long, slender, rounded, point straight up, and reach same height as major cusps; crowns of large specimens of more than 100 mm standard length with major cusps weakly truncated and minor cusps small but relatively long, with slightly horizontal orientations; tooth bands short, e.g. posterior third of premaxillae bear no teeth; dental arcades very slender, outer rows separated by one tooth width from 1-2 rows of tricuspid inner teeth; inner rows diminish posteriorly, until only outer row remains (Ref. 127594). Lower pharyngeal bone 1.0-1.1 times broader than long, relatively shallow posteriorly, and keel equally deep to distinctly deeper than posterior part of bone; pharyngeal teeth uni- to weakly bicuspid and slender; major cusps acutely pointed, cusp gaps slightly concave, minor cusps very small to absent; all rows with similar-sized teeth; posterior edge of bone set with 30-32 teeth with acutely rounded major cusps and small minor cusps (Ref. 127594). All gill rakers on outer row of first gill arch short, stout, and unifid (Ref. 127594). Caudal fin emarginate and its posterior margin dorsally and ventrally rounded; dorsal and anal fins extend to 1-2 scale lenghts before caudal fin base; pectoral fins of all specimens and pelvic fins of juveniles reach to just before anus; pelvic fins extend to anal fin base in males (Ref. 127594).

Colouration: Live colour pattern of mature males: dorsum, caudal peduncle, and caudal and pectoral fins olive-green; snout slightly darker with a blue hue dorsally; eyes dark and flanks, opercula, cheeks, extension of caudal fin, and spines of anal fin bright red; belly and branched rays of anal fin whitish, latter with three relatively small, bright yellow to orange egg spots, i.e. size slightly larger than distance between adjacent fin rays; branched rays of dorsal fin hyaline and with black lappets, i.e. extensions of membranes between spines; two longitudinal stripes just above upper and lower lateral lines; lower one runs from eye, over opercular blotch, to caudal fin base; upper stripe runs over anterior part of dorsum; lachrymal, nasal, interorbital, and supraorbital stripes, nape band, and mental blotch present (Ref. 127594). Live colour pattern of juveniles: body and pelvic fins white-gold; head and body without distinct markings, except for opercular blotches; dorsal fin dusky, caudal fin dark-greenish, and anal fin yellow (Ref. 127594). Colour pattern in alcohol: body brownish, mature males with two longitudinal stripes above upper and lower lateral line; lachrymal, nasal, interorbital, and supraorbital stripes, nape band, and mental blotch present; markings of preserved females unknown; juveniles without distinct markings, except opercular blotch (Ref. 127594).