Diagnosis: Marcusenius devosi can be distinguished from its congeners by the following characters: distance dorsal fin origin to end of caudal peduncle 39.5-43.4% of standard length, preanal distance 57.0-61.0% of standard length, predorsal distance 59.8-64.0% of standard length, caudal peduncle length 19.2-22.1% of standard length, number of scales in linear series along the lateral line row 56-66, dorsal fin rays 21-24, anal fin rays 26-30, and 14-18 scales around caudal peduncle (Ref. 75962). Electric organ discharge lacking weak head-negative pre-potential, strong Namp relative to Pamp, but short Ndur, Pdur of long duration (Ref. 75962).
description: Head with terminal mouth well in front of eye, mental lobe on lower jaw protruding beyond upper jaw; head and body dorsolaterally compressed (Ref. 75962). Dorsal fin situated about two thirds of standard length from snout, obliquely orientated, anteriorly higher and posteriorly lower, distal margin sometimes only slightly crescentic with anterior two or three rays longer than posterior rays, number of rays 21-24; anal fin opposite dorsal fin with distinctly more anterior origin, obliquely orientated, anteriorly lower and posteriorly higher, anterior rays longer than posterior ones, especially in males where they also appear stronger and often darkened, distal margin crescentic, number of rays 26-30 (Ref. 75962). Scales cycloid with reticulate striae, scales extending anteriorly to operculum and pectoral fins; scales on caudal peduncle circumference, 14-18 (Ref. 75962). Caudal peduncle relatively deep, subcylindrical enire length, usually 19.0-21.0 on standard length (Ref. 75962). Electric organ discharge biphasic lacking a weak pre-potential, Pamp of relatively long duration, increasing with standard length at least in females and juveniles, Ndur of very short duration, but very strong Namp; no sexual dimorphism recognized (Ref. 75962).
Colouration: Colour in preservation: head and back when seen from above, dark; body sides light brown to light ochre, the ochre found especially on lower parts and underside; dorsal fin usually darker than anal fin; homogeneous colouration without any blotches, increasingly lighter from back to belly (Ref. 75962).