Relative importance of family, site, and field placement timing on survival, growth, and yield of hatchery-produced Pacific oyster spat (Crassostrea gigas)

Abstract

Summer mortality has been reported in the Pacific oyster, Crassostrea gigas, for many years in different parts of the world. The causes of this phenomenon are complex. The multidisciplinary program "MOREST", coordinated by IFREMER, was initiated to understand the causes of summer mortality of Crassostrea gigas juveniles in France and to reduce its impact on oyster production. Within this program, three successive groups of bi-parental families were bred in a hatchery in 2001 and placed in the field during summer in three sites (Ronce, Rivière d'Auray, and Baie des Veys). This paper reports the relative importance of family, site and field placement timing for three characters of major importance for oyster production: survival, growth, and yield. At the end of the summer period, significant differences for the three characters were observed among sites and families for each group. Family effect was the largest variance component for survival, representing 46% of the total. Variance component analysis revealed that variation in yield among families depended either on survival or on growth according to the site. Significant family × environment interactions were observed for yield and survival but not for growth. No difference in survival was found among groups in the three sites at the end of the experiment, but a critical period of mortality was identified from late July until early September. The influence of environmental conditions, notably on reproductive allocation and its relationship with the studied traits, is discussed.

Summer mortality of hatchery-produced Pacific oyster spat (Crassostrea gigas). I. Estimation of genetic parameters for survival and growth

“…The causes of the summer mortality phenomenon are complex and depend notably on environmental factors that are impossible to control in field experiments. As heavy mortality was observed in some of our families in each set, we concluded that environmental conditions were conducive to summer mortality for each of our three successive sets (Dégremont et al, 2005a).…”

“…The importance of field placement timing (i.e. differences between sets) on the studied traits in this experiment was previously discussed by Dégremont et al (2005a).…”

“…Several authors have suggested that a significant genetic component exists for resistance to summer mortality and that selection could improve this trait (Beattie et al,, 1980;Hershberger et al,, 1984, Dégremont et al, 2005a but heritability estimates for summer mortality had not been determined up to now. In our study, juvenile C. gigas mortality ranged from 2 to 82% during summer, similar to levels observed by Beattie et al, (1980) and Perdue et al, (1981).…”

“…Because yield is the result of survival and growth, it is important to determine if this genetically determined variation in yield is primarily driven by differences in growth, survival or both traits. This is likely to vary according to site (Dégremont et al, 2005a). In the present paper, we report heritability estimates for survival and growth during the summer period, and genetic correlations between these two traits.…”

“…In the present paper, we report heritability estimates for survival and growth during the summer period, and genetic correlations between these two traits. These genetic parameters were computed using the data from the experiment described by Dégremont et al (2005a), who suggested that there is a significant genetic component for spat survival.…”