Effects of parental strains and heterosis of the hybrid between Clarias macrocephalus and Clarias gariepinus

The hybrid between Clarias macrocephalus female x C. gariepinus male has been cultured in Thailand for more than 20 years, but the effects of parental strains have not been studied. In the present study, differences among three strains each of C. macrocephalus and C guriepinus were shown by the analyses of five microsatellite loci (F-ST = 0.174 +/- 0.037), Pairwise F-ST within species was significantly higher than zero (P 0.0000) for every population pair, and ranged from 0.027 to 0.041 for C. macrocephulus and from 0.087 to 0.254 for C guriepinus. Interspecific hybridization was performed using females from C. macrocephulus and male C. guriepinus, resulting in nine hybrid crosses. Performance trails of the hybrids were compared with the offspring of three crosses each within C. macrocephulus and C. guriepinus. The experiments were done in tanks from 28 to 84 days old, and in cages fixed in an earthen pond from 85 to 175 days old. The results showed that the effects of both parental strains and their interaction on the absolute growth rate and specific growth rate (SCR) from 28 to 84 days old were significant. Absolute growth rates during 85 to 175 days were significantly affected only by strains of C. gariepinus, while neither parental strains affected SGR from 85 to 175 days old of the hybrids. The effects of the parental strains and their interaction were not significant for other traits, including the survival rate from 28 to 84 days old and 85 to 175 days old, dress-out percentage, fillet yield, phagocytic activity and phagocytic index. It was noteworthy that the difference in traits among crosses within each genetic group (C. macrocephalus, C. gariepinus, and hybrids) was significant only for growth traits (absolute growth rates from 28 to 84 clays and from 84 to 175 clays among strains of C guriepinus, and among hybrids; the SGR from 28 to 84 days old and 85 to 175 days old within C macrocephulus, and the SGR from 28 to 84 days old within the hybrids). Mean heterosis was low and not notable (<1%) in most cases, except for the survival rate from 28 to 84 days old and 85 to 175 days old (+2.43 +/- 2.14 and +1071 +/- 4.71%, respectively), absolute growth rate from 85 to 175 days (+10.85 +/- 11.35%), and percent fillet yield (+1.34 +/- 1.73%). Variation of heterosis among the hybrid crosses was observed. Among the nine hybrid crosses, the cross between female C. macrocephalus from Udorn Thani province (Cma-UD) x C. gariepinus from the Department of Aquaculture (Cga-AQ) showed the highest proportion of positive heterosis across ten traits (90). (C) 2013 Elsevier B.V. All rights reserved.