Early prediction of long-term family growth performance based on cellular processes - A tool to expedite the establishment of superior foundation broodstock in breeding programs

In the establishment of selection programs where foundation broodstock are taken from the wild, or from unevaluated stocks, there is no prior way to ascertain their genetic merit for growth rate. However, for highly fecund multiple spawning species, selection of broodstock founders could be made more efficient if their estimated breeding values (EBVs) could be determined through progeny testing early in the production cycle. Early progeny testing could allow farmers working with unimproved species to immediately re-spawn best EBV ranked broodstock for stocking grow-out systems, thereby avoiding costs associated with rearing slow-growing families. In this study, we quantified the additive genetic (co)variation of barramundi, Lates calcarifer, larval traits which could reveal their parents innate genetic capacity for fast growth. Specifically, we investigated the heritability (h2) of cellular, biochemical and morphological larval traits (total RNA, total DNA, total protein, RNA/DNA, protein/DNA, the proportion of cells dividing and standard length, Ls) and their genetic correlations (rg) with two morphological traits at harvest indicative of long-term growth (Ls and wet weight, W). Here, two cohorts originating from partial factorial crosses between 11 dams and 26 sires were sampled at 18 days post hatch (dph) in the hatchery then later at 273-469 dph at harvest. Pedigrees were reconstructed through microsatellite based parentage analyses and genetic parameters estimated through animal models via REML. All larval traits were heritable at 18 dph (0.19 < h2 < 0.51), indicating that their expression is under additive genetic control and therefore that they could have predictive power to estimate parental EBV. This was confirmed by positive and significant rg for all larval traits (except protein/DNA) and that of fish harvest size (rg > 0.60, P < 0.01). In particular, high rg were found between larval cellular and biochemical traits RNA/DNA, total RNA and the proportion of cells dividing (0.81 < rg < 0.88, P < 0.001), indicating that larval families with higher metabolic rates also grew to be the larger and heavier families at harvest. Results showed that genetic differences in growth traits among barramundi broodstock could be determined shortly after spawning by measuring larval indicator traits predictive of long-term genetically determined growth. These larval predictive traits may allow fish breeders working with highly fecund multiple spawners like barramundi to explore the advantages of early progeny testing to expedite the establishment of superior foundation broodstock in breeding programs.