Combining ability and heterosis for growth and survival in interspecific hybrids of Tor soro, Tor douronensis and Tor tambroides

Abstract

The Indonesian mahseer (Tor sp), including Tor soro (TS), Tor douronensis (TD), and Tor tambroides (TT), are local fish with high economic, cultural, and conservation value. Domestication efforts are underway, and breeding programs to support aquaculture are anticipated. This study, conducted at the Research Center for Applied Zoology in Cibinong, Indonesia, aimed to explore the combining ability and heterosis of growth-related traits and survival rate of populations consisting of interspecific hybridization of these species at the early life stage. A complete diallel crossing resulting in nine combinations, three intraspecific and six interspecific hybrid populations, was carried out. The total body weight, body length, and survival were measured following the larval rearing for four months. Growth-related parameters including final weight, final length, absolute growth weight, absolute growth length, specific growth rate of weight, specific growth rate of length, and survival rate were recorded. Combining ability was estimated using griffing approach method 1 and model 1, in which direct hybris, reciprocals, and parental populations were involved. Mid-parent heterosis (MPH) and better-parent heterosis (BPH) were estimated. The results showed significant differences in growth-related traits and survival among the hybrid combinations. General combining ability (GCA), specific combining ability (SCA), and reciprocal effects were significant (p < 0.001–p < 0.01 in most of the traits). The GCA, SCA, and reciprocals explained 69.12%–83.47%, 4.84%–20.74%, and 8.17%–18.34% of phenotypic variation, respectively. The GCA variances were more remarkable than those of the SCA for most growth-related trait parameters but not for survival. The TT was the best combiner for growth and survival, followed by TS for survival and TD for growth. Based on MPH and BPH, the hybrid combination TT × TD performed best for growth-related traits, with MPH ranging from 5.31% to 14.64%. The performance of direct hybrids differed from their opposite, indicating the significant effect of the reciprocal. Based on the GCA to SCA variance ratio, selective breeding exploiting the additive genetic variance would be effective for long-term genetic improvement. In contrast, a hybrid combination of TT × TD and TD × TS could be recommended for short-term breeding programs.