Aspects of the reproductive biology of hatchery-raised Clarias gariepinus I: fecundity
The fecundity of four batch weights (10 samples each) of gravid Clarias gariepinus weighing 60 ± 0.17159 g 125 ± 0.15092 g 250 ±0.20683 g and 500 ± 0.15670 g raised from the hatchery was investigated The paired ovary of each fish was dissected out, weighed (g) and its length measured(mm). Each paired ovary was stored n a solution of 1 % formalin in 06 % saline soluton for at least 3 weeks for the solution to harden the eggs and remove egg clumping. After 3 weeks, each paired ovary was torn apart on a 2 mm mesh circular fabricated sieve over a stream of water. Theeggs passed through the 2 mm mesh sieve into a receptacle. Sub sample of the eggs from each paired ovary was taken, counted and all the eggs in each paired ovary were determined thereafterby volumetric method. The tota fecundy of 40 gravid fsh studed ranged rom 6,450 to 71,450 eggs per fsh. The mean fecundities of the 60 g125 g, 250 g and 500 g fsh were 8,501.9 ± 295.5,13,364.0 ± 1734.3, 41087.9 ± 12258.1 and 51,186.0 ± 13851.0 eggs respectvely. The relationships between fecundity and fish weight (FW) (n = 40, r = 0.8761), fsh ota lengh (TL) (n= 40, r = 0.8266), fsh ovarian weght (OW) (n = 40, r = 0.7609), fish ovaran length (OL) (n = 40, r = 0.7236), gonadosomatic index (GSI) (n = 40, r = 0.5992) and fsh condton factor (K) (n = 40, r = 0.9046) obtaned were linear and positive and the conditon factor appearedto be the best predictor of fecundity in C. gariepinus studied. The higher fecundity o C. gariepinus (range: 6,450 to 71450) obtaned from ths study when compared wth the range of 9,000 to 25,000 earlier reported from the wild stock indicates that hatchery-raised C. gariepinus is more fecund than the wild fish in the Anambra area of the sub-region. Therefore, hatchery-raised C. gariepinusappears to be better for fish breeding in fingerlngs production than the wild fish.
Keywords: Fecundity, Gonadosomatic index, Condition factor, Hatchery-raised Clarias gariepinus