Selective breeding for summer survival in Pacific oyster (Crassostrea gigas): Genetic parameters and response to selection

Pacific oyster (crassostrea gigas) is an economically important farmed oyster species which is now severely threatened by summer mortality all over the world. Selective breeding for natural disease resistance is an effective and sustainable method to reduce mortality outbreak. We established a basic breeding population by using two fast-growing lines and then two successive generations of selection for summer survival was conducted. The aim of this study was to estimate the genetic parameters and detect the selection response over two generations of family selection. Summer survival was defined as binary trait and analyzed by two animal models (linear animal model (LAM) and threshold (logit) animal model (TAM)). Across generations, low to moderate heritability values (0.12-0.28) were estimated for summer survival by using two different models, suggesting that this population will continue show response to future selection. The genetic correlations between summer survival and growth traits were low but positive in different generations (0.056-0.229), which implies that selection for summer survival would not result in adverse responses in growth traits. The realized genetic gain of summer survival from the G1 to G3 generation ranged from 10.71% to 13.55%. The accumulated realized genetic gain (24.26%) expressed as a percentage was 41.97%. Moreover, there were also positively correlated changes in growth traits which selected population had a higher growth than did the control population in each generation. The results indicate that there are good prospects for the genetic improvement of summer survival in C. gigas.