Response to selection for growth in three selected strains of the Pacific oyster Crassostrea gigas

Abstract

Applying successive high selection pressures in fecund aquatic animals can easily lead to high increases in inbreeding and, consequently, to reductions in fitness and long-term genetic progress. The Pacific oyster Crassostrea gigas is one of the most commercially important aquaculture species worldwide. C. gigas from three cultured stocks in China, Japan and Korea were used to establish three mass-selected strains for fast growth, and a positive response to selection for fast growth was observed in the first two generations of these strains. To determine whether continuous progress can be achieved by selection for growth, we evaluated response to selection for the eighth to tenth generations of the three breeding strains. At grow-out stage, a genetic gain of 8.8–15.2%, selection response of 0.506–0.786 and realized heritability of 0.275–0.420 for shell height were observed in the selective breeding strains after seven to nine generations of selection. For body weight of oysters at grow-out stage, an average of 8.12–12.47% in genetic gains and 0.358–0.706 in selection responses were also obtained in the three mass-selected strains. The current response to selection for growth obtained in the eighth- to tenth-generation selection strains suggests that a large amount of genetic variance still remains in the selected strains and there is a potential for sustained genetic improvement in growth-related traits in these strains through selective breeding. The results obtained in this study provides important information for future breeding programmes for C. gigas.