Sex ratio distribution and fecundity of the claroteid catfish Clarotes laticeps in the lower reaches of the River Niger

Abstract

Sex ratio distribution and fecundity of Clarotes laticeps were investigated between January 2010 and December 2012 in the lower River Niger. Samples were collected every two weeks for 36 months from six sampling sites, using a combination of baited longlines, gill nets and cast nets. Sexes of captured specimens were determined by macroscopic examination of gonads. Fecundity was estimated using gravimetric method. Differences in sex ratio distribution were statistically determined by Chi-square (x²), while relationship between length and fecundity, and length and weight were determined by multiple regression analysis. Sex ratio distribution varied greatly with respect to time and space, with an overall sex ratio of 3:2 (male: female). Mean fecundity recorded was 8,247 eggs, least fecundity, 3,100eggs, while maximum eggs, 17, 320 eggs. Mean relative fecundity was 6.3, while least value recorded was 3.8 and maximum of 8.8. Mean relative fecundity estimates were generally higher in the smaller sizes than in the larger ones. Wide variations in fecundity were observed among fish of the same size and size categories, as well, as between different sizes. Correlation between length, weight and fecundity showed that length rather than weight was a better predictor of fecundity in C. laticeps in the environment studied.

Keywords: Sex ratio, fecundity, Clarotes laticeps, River Niger