Genetic components of growth traits of the hybrid between ♂North African catfish (Clarias gariepinus Burchell, 1822) and ♀bighead catfish (C. macrocephalus Gunther, 1864)

The hybrid between male North African catfish (Clarias gariepinus Burchell, 1822) (Cga) and female bighead catfish (C. macrocephalus Gunther, 1864) (Cma) is economically important in Thailand and neighboring countries, with annual production of about 120,000 t However, genetic approach for improvement of the hybrid has not previously been considered. In this study, five families each of fast- and slow-growing male Cga and female Cma were hybridized following a partial factorial mating scheme. The mating resulted in 40 full-sib families with 10 paternal half-sibs and 7 maternal half-sibs. They were tagged and communally reared in two earthen ponds for 77 days. Variance components for body weight (BW), total length (TL) and standard length (SL) of the hybrids were estimated at 207 days old using the PROC MIXED procedure of SAS 9.0 following a model that accounted for initial size (family mean at commencement of communal rearing) and sex of the fish as fixed effects, and for sire, dam, sire x dam, and residual as random effects. The results revealed that general combining ability (GCA) of male Cga (362.64 for BW, 0.25 for SL and 0.29 for TL) was higher than that of the Cma females (190.32 for BW, 0.23 for SL and 0.25 for TL). Specific combining ability of both males and females (63.19 for BW, 0.14 for SL and 0.08 for TL) was much lower than the GCA. These results imply that growth performance of the hybrid depends largely on additive genetic variation of the male parent followed by that of the female parent. As such, growth of the hybrid can be improved by selective breeding to enhance growth of the parental strains. Further study is also recommended to evaluate genetic correlation of a chosen trait between purebred parental strains and the hybrid, which may enable a more efficient approach in selection to improve hybrid performance.