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Petrocephalus longicapitis Kramer, Bills, Skelton & Wink 2012
Subfamily: PetrocephalinaeGenus: Petrocephalus
Original description from Kramer et al (2012):
Body oval shape. Head broadly rounded with a small ventrally positioned subterminal mouth, situated ventral to the eye; head and body dorsolaterally compressed. Dorsal fin (a) origin situated about two-thirds of standard length from snout, (b) obliquely orientated, anteriorly higher and posteriorly lower, (c) distal margin crescentic with anterior two or three rays longer than posterior rays, and (d) number of rays 21 (n = 2), 22 (n = 10), 23 (n = 21), 24 (n = 3), 25 (n = 2). Anal fin (a) longer than dorsal fin, (b) opposite dorsal fin with slightly more anterior origin, (c) obliquely orientated, anteriorly lower and posteriorly higher, (d) anterior 10 or so rays longer than posterior ones, especially in males where they also appear stronger, (e) margin broadly rounded, (f) rays posterior to first 10 with distal margin straight, (g) number of rays 26 (n = 1), 27 (n = 1), 28 (n = 23), 29 (n = 11), 30 (n = 2). Forked tail fin with rounded lobes. Scales cycloid with reticulate striae, scales extending anteriorly to operculum and pectoral fins (beyond pelvics). Scales in lateral series, 37 (n = 3), 38 (n = 8), 39 (n = 1). Scales on caudal peduncle circumference, 12 (n = 38). Caudal peduncle slender, subcylindrical entire length, usually 19.9% (18–21.5%) of SL.
Electric organ discharge, triphasic pulse with strong head-positive phase P1 followed by head-negative main phase N, and weaker head-positive P2 phase (Figure 10); P2 phase stronger in males than in females of same size. Pulse duration short [mean 379 μs (range 298–642) in females (n = 19) and 354 μs (253–473) in males (n = 15), respectively; 25◦C, 2% threshold criterion]. Males with kink in anal fin base, which is absent in juveniles and females where the anal fin base is straight.
Colour in life: grey-silver, underside lighter, paired fins light and transparent.
Colour in preservation: light brown.