Diagnosis: Marcusenius lucombesi can be distinguished from its congeners by the following characters: distance dorsal fin origin to end of caudal peduncle 40.0-43.2% of standard length; distance anal fin origin to end of caudal peduncle 43.6-45.9% of standard length; pre-anal length 56.6-59.2% of standard length; pre-dorsal length 59.5-63.3% of standard length; low caudal peduncle depth 25.0-30.8% into its length; circumpeduncular scales 14-16; anal fin rays 28-29; dorsal fin rays 22-24; total vertebrae 44; lateral line scales 55-56; anterior gill rakers (4-5)+(4-5); total anterior gill rakers 8-10; posterior gill rakers (6)+(7); total posterior gill rakers 13; jaws with 5-5 conical teeth (Ref. 95448).

Description: Head with terminal mouth well in front of eye, mental lobe on lower jaw protruding in front of upper jaw; head and body compressed; snout very pointy; pre-anal distance shorter than pre-dorsal distance; distance from origin of anal fin to origin of dorsal fin equal to the middle body depth; pre-pelvic distance twice as long as the distance between pelvic and anal fins (Ref. 95448). Dorsal and anal fins set well back on the body, situated about two thirds of standard length from the snout and opposite each other; dorsal fin shorter, originating on vertical at 3rd anal fin ray and ending before anal fin base; distal margins of dorsal and anal fins obliquely orientated, with rays becoming gradually shorter posteriorly; dorsal fin rays 22-24, its anterior rays highest, with distal margins rounded and slightly concave; anal fin rays 28-29; anterior anal fin rays of sexually mature males longer, appear stronger, are crescentic and rounded, but are anteriorly sharp and pointy in females and juveniles; pectoral fins rays 10; pectoral fins distinctly very long, reaching origin of pelvic fin (Ref. 95448). Middle body depth 25.0-28.4% of standard length; caudal peduncle thinner, subcylindrical across its entire length 19.7-21.7% of standard length; caudal peduncle depth 25.0-30.8% into its length (Ref. 95448). Lateral line scales 55-56; lateral line scales cycloid with reticulate striae; 14-16 scales along the caudal peduncle circumference (Ref. 95448). Jaws with 5-5 conical teeth; 44 vertebrae; gill rakers on anterior side covered with many minute spines, total anterior gill rakers 8-10 on the first gill arch; total posterior gill rakers 13 on the posterior side of first gill arch; gill rakers on posterior side shorter, thicker and covered by minute spines (Ref. 95448).

Colouration: light brown when preserved; homogeneous colouration without any blotches, increasingly lighter on belly (Ref. 95448).