ABSTRACT

 Hybridization studies were carried out on the offspring of 15 mating combinations derived from three clariid catfishes: Clarias gariepinus, Heterobranchus bidorsalis and H. iongflhis. Eggs and mitt of the parents were mixed together to generate the combinations after the selected females had been injected intramuscularly with Ovaprim at a dose of 0.5 mt/kg of fish weight. During the indoor and outdoor growth of the fry and fingerlings for the first 7 weeks, a comparison of the initial weight, final weight, weight gain and specific growth rate (SGR) showed that the hybrids of the intergeneric combination, Heterobranchus bidorsalis x C/arias gariepinus (Sb) were more outstanding with an SGR value of 13.09 when compared to the others while at the end of the grow-out period, C. gariepinus (Nb) x H. longfluis intergeneric hybrids showed a higher final mean weight of 251 .55g although the SGR values were not significant (p > 0.05). In terms of survival, the hybrid offspring of C. gariepinus (Nb) x H. long/fl/is had the highest percentage survival of 87% as compared to the least survival of 30% exhibited by offspring of C. gariepinus (sb) x C. gariepinus (Nb) at the end of the fingerling production stage. During the twelve months of grow-out, the offspring of H. bidorsalis x C. gariepinus (Nb) and H. bidorsalis x H. bidorsalis had the highest percentage survival of 95% while the least value of 55% was obtained for the hybrids of C. gariepinus (Nb) x H. long/fl/is. A significant association occurred between the mating combination and the sexes of offspring produced as C. gariepinus (sb) x H. bidorsalis and C. gariepinus (Nb) x H. bidorsa/is produced significant sex ratios of 1:3.71 and 1:18.5 respectively (p < 0.05). The fecundity and gonadosomatic indexes of the various offspring also varied during the two seasons (years) considered. The fecundity of the various offspring varied between 73/kg and 219,705/kg body weight. xi There was also the general indication that the offspring of the Clarias gariepinus stocks of the parental combinations and their intraspecific crosses produced the highest number of eggs while the least came from the intergeneric hybrids. The females had higher gonadosomatic indexes than the males. Additional histological analysis of the gonads (ovaries and testes) showed that the various hybrids have a high reproductive potential. Based on some of the characters that accounted for most of the variations, four major groups among the offspring were revealed from a plot of axes 1 and 2 that accounted for 92.48% of the total variation recorded at the end of a canonical discriminant analysis. The Mahalanobis square distance (D2) between the offspring of the various mating combinations also revealed varying levels of relationship between the offspring based on their morphometric and meristic characters. Varying numbers of bivalent chromosomes were also observed and presented for the different offspring.