Selection response and realized heritability for growth in three stocks of the Pacific oyster Crassostrea gigas

To estimate response to selection and realized heritability for shell height, a one-generation selection was performed in the Pacific oyster Crassostrea gigas using three stocks from China (stock C), Japan (stock J), and Korea (stock K). Applying about the same intensity of selection in the upward direction, three selected and three control lines were created, which were reared under the same environmental conditions at larvae, spat, and grow-out stages. Stock C and stock J showed significantly higher response to selection and realized heritability than stock K at spat and grow-out stages (P < 0.05). At harvest on day 360, the selected lines of stocks C, J, and K were 12.2, 12.2, and 7.9% larger than their control lines, respectively, for shell height. When averaged across the grow-out period, the genetic gain for stocks C, J, and K was 13.2 +/- A 1.2, 13.2 +/- A 1.0, and 7.2 +/- A 0.7%, respectively, and realized heritability was 0.334 +/- A 0.028, 0.402 +/- A 0.024 and 0.149 +/- A 0.027, respectively. The relatively high realized heritability estimate obtained for stock C and stock J indicates that there is genetic variation in the two stocks and that selective breeding by mass selection is very promising.