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Dorsal spines (total): 0-0; Dorsal soft rays (total): 20-26; Anal spines: 0-0; Anal soft rays: 26-30. Diagnosis: Marcusenius altisambesi can be distinguished from its congeners by the following characters: scales around caudal peduncle 12-14; scales in linear series along the lateral line row 49-60; anal fin rays 26-30; dorsal fin rays 20-26; and body depth 20.1-32.8% of standard length (Ref. 75962). Electric organ discharge (EOD) with weak head-negative pre-potential in juveniles and females, sexual dimorphism in EOD waveform present in the 'summer' in the form of greatly increased EOD duration in sexually mature males of greater than about 12.5 cm standard length, but dimorphism not confirmed for specimens from Okavango (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 20-26; 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 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, 12-14 (Ref. 75962). Caudal peduncle relatively deep, subcylindrical entire length, 16-22% of standard length (Ref. 75962). Electric organ discharge biphasic with weak pre-potential in juveniles and females; in sexually mature males greater than about 12.5 cm standard length, sexual dimorphism in the form of greatly increased EOD duration in 'summer', not confirmed for specimens from Okavango (Ref. 75962).
Colouration: Colour in life: beige-grey, head yellow-gold with greenish hue, paired fins yellow, dark brown blotches except on head, fewer on belly, purple shimmer depending on the angle of light incidence; Okavango specimens similar but darker, brownish grey with many distinct dark-brown blotches, less on belly, paired fins beige rather than yellow (Ref. 75962). Colour in preservation: medium brown with darker, irregular blotches on the sides, narrow dark zone on the back not seen from side, belly same colour as body sides, darkness of head reduced by opaque mormyrid skin; Okavango specimens similar but clearly darker, including the fins (Ref. 75962). |