Diagnosis: Haplochromis coprologus is a small sized (less than 8 cm standard length), micrognathic species with a diamond-shaped body outline, dorsal head profile straight to incurved above the eye; mouth oblique with relatively small, mainly bicuspid teeth (Ref. 85523). It differs from Haplochromis erythrocephalus, the only other described small species with similar body outline, in live colouration of sexually active males: H. coprologus is almost completely black, whereas H. erythrocephalus has a bright red head and the remainder of the body colouration is yellowish; further, differences are present in interorbital width, snout length, eye length, lower jaw length and the lower jaw length/width ratio (Ref. 85523). Haplochromis coprologus differs from the similarly coloured H. piceatus mainly in body depth, which is higher in H. coprologus than in the sympatric population of H. piceatus from the Mwanza Gulf, and a larger eye length (Ref. 85523). The reddish parts in the caudal and anal fin of H. coprologus are generally smaller than in H. piceatus; moreover, in H. coprologus these parts are generally dark red and in H. piceatus orange to orange-red (Ref. 85523). Haplochromis coprologus differs from H. antleter, which has a similar male colouration, in its dorsal head profile which is straight to incurved above the eye in H. coprologus and moderately curved in H. antleter; the lower jaw in H. coprologus is longer, narrower and more oblique than in H. antleter; the number of gill rakers on the lower part of the first gill arch is higher in H. coprologus, 11-12, than in H. antleter, 10 (Ref. 85523).

Description: Body outline diamond-shaped; dorsal head profile straight to incurved above the eye; premaxillary pedicel often slightly interrupting the profile (Ref. 85523). Mouth oblique; lips not thickened; medial part of the premaxilla slightly expanded; caudal part of the maxilla not bullate; the vertical through the caudal tip of the maxilla runs through the iris, sometimes through the pupil; lateral snout outline isognathous to slightly prognathous, obtuse; if isognathous, lower jaw not or slightly protruding; mental prominence slightly pronounced; retro-articular processes of right and left mandible generally touching each other, slightly interrupting the ventral body outline; eye approximately circular; aphakic aperture generally present; cephalic lateral line pores slightly enlarged (Ref. 85523). Cheek, gill cover, dorsal head surface, greater part of dorsum and caudal fin base covered with cycloid scales, the remaining part of the body with ctenoid scales; a gradual size transition between scales of chest and flank; four and a half to six scales between the upper lateral line and the dorsal fin origin, four to six between the pectoral and the pelvic fin bases (Ref. 85523). In females the pelvic fins just reach the anal fin origin; in males the pelvic fins reach the anal fin origin, sometimes extending further; first soft rays of pelvic fins may be produced and filamentous in males; anal fin just reaching caudal fin origin; caudal fin outline truncate to emarginate (Ref. 85523). The number of gill rakers on the lower part of the first gill arch is 11 to 12; the lower one to two rakers are reduced; the next two to three rakers are short and blunt to pointed in shape; these are followed by two to seven long and slender rakers, their shape is pointed to acutely pointed; the remaining rakers are acutely pointed to blunt or bifid; the rakers on the first gill arch are touching each other; the number of gill filaments on the lateral hemibranch of the first gill arch ranges from 84 to 104 (Ref. 85523). Premaxillary dentigerous arm as long as or slightly shorter than ascending arm; the angle between the two arms is 82° to 86°; symphyseal articulation facet not present; lower jaw is relatively elongated; the upper half of the dentary has a distinct outwardly directed flare; a small mental prominence is present on the chin; teeth in the rostral part, ca. 2/3 of dentigerous area, of premaxilla and lower jaw generally unequally bicuspid, often with a few tricuspids among them; teeth in caudal part of premaxilla are small, weakly tricuspids or blunt unicuspids; teeth in caudal part of lower jaw are small subequally bicuspids, weakly bicuspids or tricuspids; in bicuspid teeth, the shape of the major cusp is isoscelene to subequilateral; a small, not very distinct flange is present on rostrally positioned teeth, in caudally positioned teeth it is hardly visible or absent; the cusp gap is wide, the minor cusp is distinct; in labial view the neck is moderately slender, the crown not to slightly expanded; in lateral view, the crown is compressed; the premaxilla outer row teeth are slightly to strongly recurved; those of the lower jaw are slightly recurved; the inner row teeth of both premaxilla and lower jaw are tricuspid; teeth relatively small and slender; caudal teeth of premaxilla very small, deeply embedded in tooth gum (Ref. 85523). Dental arcade rounded and U-shaped; premaxilla generally has two, rarely three inner rows anteriorly, none posteriorly; lower jaw with one to two inner rows anteriorly, none posteriorly; in the dissectioned female the caudal-most quarter of the dentigerous arm is edentulous, in males the edentulous part is much smaller; there are 51 to 63 teeth in the outer row of the upper jaw; the setting varies in both premaxilla and lower jaw from closely to widely and regularly set; caudally, teeth may be more widely set than rostrally; outer row teeth of premaxilla erect, inner row teeth recumbent; lower jaw outer row teeth slightly procumbent, inner row teeth erect (Ref. 85523). Lower pharyngeal element relatively long and slender; longer than broad; the dentigerous area is broader than long; the suture is straight; there are 37 to 40 pharyngeal teeth in caudal-most transverse row, 10 to 12 teeth in the medial length rows; teeth in caudal-most transverse row hooked, major cusp only slightly incurved and blunt; other teeth pronounced or bevelled; all teeth relatively fine and slender, medial teeth not coarser than other teeth (Ref. 85523). The total number of vertebrae is 28-30, comprising 12.-13 abdominal and 16-17 caudal vertebrae (Ref. 85523).

Colouration: Live colouration of males: snout, dorsal head surface, lips, lower jaw, interoperculum, cheek, gill cover, belly and ventral side black; dorsum, flank and chest are black with a silvery sheen; the eye has a very dark grey outer ring and an orange-yellow inner ring; an opercular blotch may be visible; pectoral fins hyaline, pelvic fins black; anal fin dusky, with variable amount of red and two to three yolk-yellow egg dummies with a dusky ring; caudal fin dusky, with a variable amount of dark-red in the caudal-ventral part; dorsal fin dusky with a black base, lappets black (Ref. 85523). Live colouration of females: entire body silvery to light brownish (Ref. 85523). Preserved colouration of males: body grey-brown to dark brown; operculum sometimes partly silver; snout, lower jaw and branchiostegal membrane sometimes darker than remainder of the head; an opercular blotch is present; pectoral fins brownish-hyaline, pelvic fins black; anal fin greyish-hyaline, sometimes with a dusky base; dusky rings around the egg dummies are occasionally present; caudal fin brownish with a dark base and a dark medial part, dorsal fin brownish, lappets black (Ref. 85523). Preserved colouration of females: body sandy-brown; snout, cheek, gill cover, dorsal head surface and dorsum darker than flank; belly, chest and ventral side lighter than flank, more yellow-brownish; opercular blotch present; pectoral fins brownish-hyaline; pelvic and anal fins hyaline; caudal fin hyaline with a brown base; dorsal fin brownish-hyaline, lappets brown (Ref. 85523).