| Diagnosis: |
Diagnosis: Petrocephalus zakoni is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics: dorsal fin with 23 or 24 branched rays; anal fin with 27 or 28 branched rays; eye large, the ratio head length and eye-diameter between 3,1 and 3,3; mouth small, the ratio head length and mouth width between 4.4 and 5.0; 10 teeth of fewer in the upper jaw; and 22 teeth or fewer in the lower jaw (Ref. 85331). It has a unique pigmentation pattern consisting of three well defined black patches: (1) an intense dark mark on each side of the body close to the anterior base of the dorsal fin, often extending onto the first dorsal rays, forming a characteristic saddle across the dorsum; (2) a mark on each side of the body at the base of the pectoral fin; (3) a crescent-shaped mark on each side of the body centered at the base of the caudal fin, extending onto the upper and lower parts of the caudal fin (Ref. 85331).
Description: Body ovoid, longer than high, the ratio standard length and height between 2.5 and 2.8; and laterally compressed (Ref. 85331). Head length between 3.4 and 3.7 times in standard length (Ref. 85331). Eye large compared to many Petrocephalus species, the ratio head length and eye-diameter between 3.1 and 3.3 (Ref. 85331). Snout short, the ratio head length and snout length between 6.1 and 8.5, and round; mouth small, the ratio head length and mouth width between 4.4 and 5.0, and subterminal, opening under the posterior half of the eye (Ref. 85331). Teeth small and bicuspid, 6-10 in a single row in the upper jaw, 18-22 in the lower jaw (Ref. 85331). Caudal peduncle thin, the ratio caudal peduncle length and caudal peduncle height between 1.9 and 2.3 (Ref. 85331). Dorsal and anal fins originate in the posterior half of the body; pre-dorsal distance roughly equal to the pre-anal distance; dorsal fin with 23-24 branched rays; anal fin with 27-28 branched rays (Ref. 85331). Scales cover the body, except for the head; lateral line visible and complete with 36-38 pored scales along its length; 12-14 scales between the anterior base of the anal fin and the lateral line; 12 scales around the caudal peduncle (Ref. 85331). Skin on head thick, becoming opaque with formalin fixation; knollenorgans on the head are not clustered into rosettes but appear as isolated receptor pores (Ref. 85331).
Colouration: Body uniformly white-silver, with the presence of three characteristic pigmentation marks: a very distinctive black mark just below the anterior base of the dorsal fin on each side, often extending onto the first dorsal rays and making contact over the dorsum with the contralateral mark; a blackish mark, sometimes weak but always visible, at the base of the pectoral fins; and a crescent-shaped black mark centered at the base of the caudal fin on each side, extending onto the upper and lower parts of the caudal fin; fins otherwise translucent (Ref. 85331). |