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Abstract

In a selective breeding program for the Portuguese oyster, Crassostrea angulata, oysters are cultured in several environments including the broodstock for breeding (Cat Ba) and production (Van Don) locations. This raises the potential that a genotype by environment interaction may occur and oyster genotypes may re-rank across environments. Whole weight and uniformity in weight at the time of harvest are two of the most important economic traits for oyster production in northern Vietnam. Limited information, particularly with respect to uniformity, exists for C. angulata. Our primary aim was to quantify the genetic variance in harvest whole weight and its uniformity and the genetic correlation between them using a double hierarchical generalized linear model. We investigated the degree of genotype by environment interaction on the uniformity of harvest whole weight in the two environments. Since the weights had a skewed distribution, we also investigated the affect of log-transformation on the estimates of the genetic variance in harvest whole weight, its uniformity, the genetic correlation between them and on the genotype by environment interactions. Results showed that heritability estimates for uniformity of harvest whole weight were low for Cat Ba (0.07) and Van Don (0.06) environments using standardized data, while these estimates were lower using log transformation for both environments. There was no re-ranking of oysters with regard to harvest whole weight and uniformity across environments; the genetic correlations were effectively one, with and without log transformation. Therefore, there is no scope to improve uniformity in the Portuguese oyster population while increasing whole weight at harvest.