Nutritional value of diets that vary in fatty acid composition for larval Pacific oysters (Crassostrea gigas)

High-light grown cells of Thalassiosira pseudonana and Pavlova lutheri constituted a superior diet for larval Pacific oysters (Crassostrea gigas) relative to the same phytoplankton species grown under low-light. Growth rates were higher and mortality was lower for those larvae fed high-light (HL) versus low-light (LL) grown phytoplankton cells of the same species. Based upon larval growth rates, these diets could be ranked: HL T. pseudonana > LL T. pseudonana = HL Pavlova lutheri > LL Pavlova lutheri, Diets consisting of T. pseudonana and Pavlova lutheri cells grown at HL and LL were similar in carbon, nitrogen, protein and carbohydrate, but not lipid content. Significant differences also existed in the fatty acid composition of the diets. Diets consisting of high-light grown T. pseudonana provided the lowest proportion of the essential fatty acid 20:5n-3 and the highest proportion of the fatty acid 16:0. Larval growth rate was negatively correlated with the proportion of the essential fatty acid 20:5n-3 in their diet. Larval mortality was positively correlated with the proportions of dietary 16:0, Examination of data collected over a number of years suggests that an abundance of dietary 20:5n-3 has a strong negative effect on larval growth rates.