Aspects of the reproductive biology of Auchenoglanis biscutatus (Geoffrey St. Hilarie, 1827) in river Orogodo, Delta State, Nigeria

Abstract

Reproductive biology of the bagrid catfish, Auchenoglanis biscutatus was studied in River Orogodo, Delta State, Nigeria from January, 2006 to December, 2007. Gonad maturation was determined macroscopically and microscopically, fecundity by gravimetric method and gonadosomatic indices (GSI) calculated. Six gonad maturity stages occurred in the species in the river. The sex ratio differ significantly (X2 =5.73, p< 0.05) from the expected male to female ratio with the female constituting about 55.73% of the entire population of the species (436). The mean size at maturity for the male was 15.09 cm ±1.44 (S.L) and 46.75 g ± 15.3 (body weight) while that of the female was 15.63 cm ± 2.3 and 57.8 g ± 10.3. The species bred throughout the year as marked by the presence of ripening (stage iii) and ripe (stage IV) ovaries throughout the period of study. The gonadosomatic index (GSI) ranged from 1.76 to 3.70% with maximum values between August and December each year. Fecundity of A. biscutatus in the river ranged from 420 to 2720 for fish with a standard length of 9.3 to 27.6 cm. Fecundity was positively correlated (p< 0.05) to both standard length (r = 0.691) and body weight (r =0.7797). The GSI values increased as both standard length and body weight increases.

Key words: Auchenoglanis biscutatus, Gonadosomatic index, fecundity, River Orogodo.