Heritability of shell pigmentation in the Pacific oyster, Crassostrea gigas

The Pacific oyster (Crassostrea gigas) is a species of considerable economic importance, with among the highest global production of any cultured aquatic animal species. In the interest of increasing the value of Pacific oysters sold as “singles” for the half-shell market, we explored the feasibility of modifying shell pigmentation through selective breeding by estimating both the broad- and narrow-sense heritability of total left-shell pigmentation in C. gigas. Twenty-six full-sib families derived from parents collected from a naturalized population in Dabob Bay, WA, were spawned in the hatchery and raised in an intertidal environment for 2 years. At harvest, we sampled shells from each family and quantified their total left-shell pigmentation using digital image analysis. We estimated broad-sense heritability based on full-sib intraclass correlations and narrow-sense heritability based on midparent-offspring regression as 0.91 ± 0.38 and 0.59 ±0.19, respectively. We further examined the distributions of pigmentation levels among individuals within full-sib families and found high within-family variation in total shell pigmentation that in the majority of families was normally and continuously distributed. However, offspring within two families segregated into phenotypically distinct “lighter” and “darker” shell groups in a 3:1 ratio (χ2, P > 0.766) supporting the hypothesis that a single major gene is segregating in these families with the “light” allele being dominant over the “dark” allele. We conclude that selective breeding acting on this high additive genetic variance should be effective in altering total shell pigmentation and that further work is needed to confirm the existence and mode of inheritance of a putative major gene affecting total shell pigmentation in C. gigas.