Diagnosis: Marcusenius wamuinii can be distinguished from all small-scaled Marcusenius species by having 8 circumpeduncular scales vs. 12-16 (Ref. 121662). Within the group of large-scaled Marcusenius species, it can be distinguished from M. kutuensis and M. ghesquierei by a lower number of dorsal-fin rays, 22-25 vs. 27--31 and 32-34, and by a dorsal-fin length that is smaller than the anal-fin length, 64.5-92.2% of anal-fin length vs. larger than the anal-fin length; it differs from M. ghesquierei, M. intermedius, M. kutuensis and M. moorii by a higher number of lateral line scales, 46-53 vs. 36-45, and from M. fuscus by a lower number of lateral line scales, 46-53 vs. 54-61; it differs from M. dundoensis by a dorsal fin height which is smaller than the dorsal fin length, 70.8-96.0% of dorsal-fin length vs. both fins about the same length, and by a lower number of lateral line scales, 46-53 vs. 51-61, and a lower number of scales between dorsal and anal fin, 19-22 vs. 21-25; it can be distinguished from M. schilthuisiae by a lower number of anal-fin rays, 27-31 vs. 32-35; it differs from M. kaninginii and M. sanagaensis by its lower caudal peduncle depth, 4.4-5.9% of standard length vs. respectively 6.8-7.7% and 6.1-6.3%, which is also an additional difference to distinguish it from M. intermedius and M. moorii; it differs from M. kaninginii by a higher number of scales between dorsal and anal fin, 19-22 vs. 16-19, and between dorsal fin and lateral line, 9-11 vs. 6-9; and from M. sanagaensis by its lower number of dorsal-fin rays, 22-25 vs. 24-28, a lower number of scales between dorsal and anal fin, 19-22 vs. 22-28, between dorsal fin and lateral line, 9-11 vs. 11-14, and between pelvic fin and lateral line, 9-12 vs. 12-14 (Ref. 121662).

Description: Body rather elongated, with highest body depth at anal-fin origin, and with straight to convex dorsal profile; caudal peduncle slender, its depth just behind anal fin about the same as its depth at the middle (Ref. 121662). Head profile convex; mouth terminal with small submental protuberance; snout rounded and blunt; single row of bicuspid teeth in upper and lower jaw, 4-5 in upper and 3-6 in lower jaw; eyes on anterior part of head; lower nostril more posteriorly on head than upper one (Ref. 121662). Preanal distance shorter than predorsal distance; dorsal-fin base shorter than anal-fin base; dorsal fin origin situated slightly behind anal-fin origin; dorsal- and anal-fin heights smaller than their lengths; dorsal-fin rays 22-25; anal-fin rays 27-31; pelvic-fin rays 6; pectoral-fin rays 9-10, pectoral fin about twice as long as pelvic fin; caudal fin deeply forked (Ref. 121662). Scales small just behind head, becoming gradually larger towards caudal peduncle; 46-53 lateral-line scales; 8-9 scales around caudal peduncle; 19-22 scales between dorsal and anal fin; 9-10 scales between dorsal fin and lateral line; 9-11 scales between pelvic fin and lateral line (Ref. 121662).

Colouration: In life: overall body colour silvery, more yellowish dorsally and more whitish ventrally; fins greyish and translucent; dorsal and caudal fin yellowish at their bases; caudal fin dark grey near its base; transverse black band on flanks visible in preserved specimens is absent or only vaguely visible in vivo (Ref. 121662). Preserved specimens: overall colour pattern brownish, dark brown on head, dorsal part of body and caudal peduncle, lighter ventrally; a transverse black band on flanks, starting close to dorsal-fin origin, extending ventrally through the entire depth of the flanks and covering two, sometimes three subsequent scales of the lateral line, and ending slightly behind the anal-fin origin; fins greyish, with the anterior portions of dorsal and anal fin darkened (Ref. 121662).