Sexual Dimorphism in Erpetoicthys calabaricus from a Mangrove Creek, Nigeria

Sexual dimorphism of E. calabaricus is presented based on the examination of external morphology of the fish. Females had very pointed anal fins which joined the caudal fin smoothly with fewer than 10 spikes. Males had broader anal fin clearly separated from the caudal fin with between 9 and 12 spikes on the fin. Colour dimorphism in males tended towards an olive green, whereas the females had a light yellow-brown colour. Paired t-test showed that active females were slightly heavier than similarly-sized males. Length frequency distribution showed the largest fish was 39.9 cm TL female, while the smallest fish (TLmin) was 21 cm TL male. Sex ratio was in favour of males giving a male: female ratio of 1: 0.79 which was different from the expected 1: 1 ratio (χ2 = 9.110, df = 1, p < 0.05). The smallest female and male were 21.7 cm and 21 cm TL, thus delineating minimum sizes in the population. Largest female and male fishes measured 39.9 cm and 39.7 cm TL. Median sizes were 28.0 cm (females) and 29.0 cm (males).