Genetically improved lines of the eastern oyster (Crassostrea virginica) have been produced through selective breeding to expand the commercial oyster aquaculture industry. The Aquaculture Genetics and Breeding Technology Center (ABC) at the Virginia Institute of Marine Science has been engaged in family breeding of the eastern oyster for over two decades; resulting in considerable gains in economically important traits including survival, growth and meat yield. Shell shape characteristics, such as fan shape and cup depth, are routinely monitored and incorporated into a multi-trait selection index. The shell trait of “hook” at the hinge has been observed in some cultured lines of eastern oysters and can make oysters more difficult to shuck. Previous analyses indicate that the hook shell trait is heritable and can be modified through selective breeding.
In Fall 2023, evaluation of the hook shell trait was incorporated into routine ABC monitoring of shell shape characteristics to estimate heritability and genetic correlation with other shell characteristics. Initial analysis of the hook trait was evaluated on a scale of –2 to +2, with 0 indicating no hook present and easy to shuck, –2 indicating the hinge was very curved up toward the flat side of the oyster and +2 indicating the hinge was very curved down toward the cup. The hook trait was evaluated in 8,027 18-month-old oysters from 78 families grown at three field locations which vary in salinity and disease exposure. Restricted maximum likelihood methods were used to estimate multi-variate genetic parameters of the hook shell trait over all samples and for each field location separately. The heritability estimate for the hook shell trait over all samples was 0.22 ± 0.07, and ranged from 0.19 to 0.39 at each of the three field locations. Over all samples, positive genetic correlations were observed between the hook shell trait and total weight (rg = 0.37) and meat yield (rg = 0.18), but negative genetic correlations were observed between hook and width index (rg = -0.51) and height index (rg = -0.22). Although these results are only from one year of evaluation with an imprecise scale, they suggest that the hook shell trait has moderate heritability and can potentially be modified through selective breeding.