Reproductive Biology and Induced Breeding in Clarias Species in Anambra River Basin, Nigeria

Abstract

Natural breedinq cycles, fecundity and s i z e a t rnaturi.ty of Cl a r i a s l a z e r a Cuvier and Valenciennes, 1840 and C l z i a s a n q u i l l a r i s Linnaeus, 1762 i n Anambra r i v e r basin, Nigeria were studied. The efficacy of human c M o n i c gonadotropin (HCG), p i t u i t a r y e x t r a c t of Clarias albopunctatus and the frog, Rana ,elegans i - . n inducicg the ovulation of the two species was evaluated. HCG was used t o imluce the two species of Clarias t o breed i n aquaria durinc; and out of t11~i.nr aturaI breeding seasons. The r e s u l t i n g hatchling were then rearctl upto early fingerling s i z e under d i f f e r e n t conditions of food and. l i g h t . The ovari.cn cycle of both species was divided i n t o early prepar a t o r y ( O c t . - Jan.), l a t e preparatory (Feb. - March), prc spawning ( ~ p r i-l ~ a y ) ,sp awning (June - July) and spent ( A q . - 5ept.I phases. The average t o t a l lengths and weights of -C. lazera a t maturity were 335cm and 250 g f o r rrale and 305 mm and 310 g for female while tilose of -C. a n q u i l l a r i s were 295 m and 225 g for male 2nd 295 mi a d 270 g f o r female respectively. P i t u i t a r y e x t r a c t of- C. albopunctatus, -Rana and HCG weri cqually e f i e c t i v e i n inducinq ovulation i n -C. lazera and -C. a n g u i l l a r i s. The r e l a t i o n s h i p between the reiin oocyte d i a r n c t ~ r of recipient an.' the ariount of each honnone required t o ovulzte was establisher for b ~ t h:- pecies. Induced breedin5 of - C. lazera and - C. a n y u i l l a r i s gave predictable r e s u l t s only if t h e i r mean oocyte diameter of "developingtt oocytes was above 620 Prn a ~ 6d00 ,hrespectivel.y. HCG-inducec! ovulated eggs of both species remained viable for f e r t i l i z a t i o n u p t o 12 hours post-ovulation. Both species were induced to breed successfully during the early preparatory phase, l a t e preparatory phase and 'spawning, phase of the ovarian cycle with no significant difference i n the mortality or growth of the fry obtained a t tlle diffeilent phase; The s u i t a b i l i t y of Torula yeast as a s t a r t e r fooc for Clarias fry was confirmed. The recorded percentage survival of fry was 31.5% for C. lazera and 90.5% f o r C. m g u i l l a r i s wl~en feeding - - was i n i t i a t e d a t 56 hours from hatching. Light was found to have a significant detrimental e f f e c t on the embryos, larvae and fry of both species. The major significance of this work is t h a t fry/finyerlinys of -C. lazera and -C, anguillaris can be produced 3 times a year tiius ameliorating trle shortage.