GENETIC CHARACTERIZATION AND IMPROVEMENT OF SHELLFISH BREEDING STOCKS FOR THE PACIFIC NORTHWEST
Location: Forage Seed and Cereal Research
Title: CAN SELECTIVE BREEDING REDUCE THE HEAVY METALS CONTENT OF PACIFIC OYSTERS (CRASSOSTREA GIGAS), AND ARE THERE TRADE-OFFS WITH GROWTH OR SURVIVAL?
Submitted to: Journal of Shellfish Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2005
Publication Date: December 31, 2005
Citation: Camara, M.D., Griffith, S.M., Evans, S. 2005. Can selective breeding reduce the heavy metals content of pacific oysters (crassostrea gigas), and are there trade-offs with growth or survival?. Journal of Shellfish Research.24(4):979-986.
Interpretive Summary: Many shellfish species accumulate heavy metals from their environment, raising health concerns for consumers. This paper examines the feasibility of using selective breeding to produce strains of Pacific oysters (Crassostrea gigas) with reduced heavy metals content. The authors produced all possible crosses among six male and five females oysters and measured four performance traits (yield, survival, whole oyster live weight and shucked meat dry weight) and the accumulated levels of four heavy metals (copper, lead, zinc, and cadmium). They found that all of these traits have a genetic basis, but there are genetic trade-offs between cadmium and copper content and performance traits. They speculate that previous selective breeding for enhanced growth and survival may have inadvertently raised the heavy metals content of oysters and that reducing the concentrations of these metals in oysters is possible. However, the genetic trade-offs they observed are likely to simultaneously result in reduced survival and growth. Clearly, these relationships should be taken into account in designing any program of selective breeding in this species.
Oyster producers in the Pacific Northwest region of the USA export large quantities of oysters to international markets. Proposed changes to international regulations on the allowable heavy metals content in shellfish could drastically curtail exports and impact the viability of this environmentally-friendly industry. “Supply-side” approaches to reducing the heavy metal content of oysters such as moving oyster farms to uncontaminated sites or short-term depuration would incur substantial costs in terms labor and infrastructure and displace workers in already economically challenged coastal communities. Selective breeding to reduce heavy metal accumulation in cultured oysters could benefit both producers and consumers within the current infrastructure. We studied the feasibility of selective breeding to reduce heavy metal content through a quantitative genetic analysis of heavy metals accumulation in the Pacific oyster, Crassostrea gigas by opportunistically sampling a factorial mating experiment initiated in 2000 to study the effects of parent size on offspring growth and survival. The experiment consisted of all possible crosses among six males (sires) and five females (dams) and was harvested in the summer of 2004. At harvest, we measured four performance traits (yield, survival, whole oyster live weight and shucked meat dry weight) and the accumulated levels of four heavy metals (copper, lead, zinc, and cadmium). Analysis of variance for sire and dam effects and bootstrap estimates of heritabilities showed that all of these traits have a genetic basis. Further, half- and full-sib family means correlations revealed genetic correlations between heavy metal content and performance traits. Copper content was positively genetically correlated with yield and survival but negatively correlated with the dry weight of shucked meats. Zinc content was uncorrelated with yield, survival, or live weight, but negatively correlated with dry meat weight. Cadmium content was positively correlated with yield and survival, uncorrelated with live weight, and negatively correlated with dry meat weight. In contrast, lead content was uncorrelated with all performance traits. Copper, zinc, and cadmium levels were mutually positively correlated but uncorrelated with lead levels. Preliminary indications are that selective breeding to reduce heavy metals accumulation is possible, but the genetic correlations between heavy metals content and performance characters should be taken into account in designing any program of selective breeding in this species.