Estimates of genetic parameters for orange shell color and their correlation with growth traits in the improved orange shell line of Pacific oyster (Crassostrea gigas)

The Pacific oyster (Crassostrea gigas) is one of the most widely farmed shellfish species in the world. With the rise in market demand for in-shell oysters, shell color trait is increasingly of interest to the breeding industry and has been a target trait for selection. In our previous breeding process, an improved orange shell line of C. gigas with a unique shell color was established by the means of hybridization and mass selection. However, the genetic parameters for shell color trait and their correlation with growth traits for the improved orange-shell line remains undocumented. This study aims to estimate genetic parameters (heritability and correlations) for C. gigas at 10 months of age by applying mixed-family approach combined with a nested mating design and CVS imaging system. In this study, heritability for shell color-related traits was estimated in the improved orange shell line of C. gigas by fostering a single cohort of 48 families consisting of 16 sires and 48 dams. A total of 863 offspring were harvested at 10-month age. Pedigree was reconstructed with 12 microsatellite markers. The shell color parameters of selected oysters were measured based on the computer vision system and Lab colorimetric system. REML based on the animal model was used to estimate the genetic parameters of orange shell color traits and correlation with growth traits of C. gigas. The results of parentage assignment showed that 98.61% of the oysters were unambiguously assigned to single parent pairs. Unbalanced contributions of parents were found among families and parents. Coefficients of variation of the progeny were 16.51%-39.62% for growth traits, and 3.70%-43.32% for shell color parameters, suggesting that there was great genetic variation among growth traits. Heritabilities of L^*, a^*, b^*, and ΔE were 0.17±0.07, 0.47±0.23, 0.42±0.21, and 0.56±0.29, respectively. The phenotypic correlations and genetic correlations of L^*, a^*, b^* and ΔE were with the ranges of –0.4-0.48 and –0.79-0.86, respectively. The phenotypic correlations and genetic correlations between the growth traits and shell color traits were low, ranging from –0.04-0.11 and –0.33-0.17 respectively. These results indicated that the breeding population had considerable additive genetic variation in orange shell color traits, and the ongoing selective breeding program should produce considerable genetic improvement in the orange shell color traits of C. gigas. However, indirect selection of growth traits using the shell color trait is infeasible due to their low correlations. Only when both the shell color traits and growth traits were selected as the targets of selective breeding, the traits could be improved. Furthermore, our studies confirmed the feasibility of the posteriori family reconstruction based on molecular markers in a communal rearing environment. The present study provides important information for future selective breeding programs for C. gigas with orange shell color trait.