STABLE ISOTOPE ANALYSIS OF THE CONTRIBUTION OF MICROALGAL DIETS TO THE GROWTH AND SURVIVAL OF PACIFIC OYSTER CRASSOSTREA GIGAS (THUNBERG, 1979) LARVAE

Stable carbon and nitrogen isotope analyses were used to evaluate the influence of microalgal diet on growth and survival of hatchery-reared Pacific oyster Crassostrea gigas larvae. D-veliger larvae were fed monospecific diets of Pavlova lutheri (P), Tahitian Isochrysis aff. galbana (T), and Chaetoceros calcitrans (C), and a standard hatchery trispecific diet of 25P:25T:50C (PTC). The dietary effects on nutrient assimilation, isotopic turnover rates, and discrimination factors were assessed using exponential models. Of the four dietary treatments evaluated over the 15-day feeding trial, larvae fed C. calcitrans and PTC had the best growth and high survival. Larvae in all dietary treatments had relatively high isotopic turnover rates (0.075-0.327/day), although some discrimination factors found in this study were out of the normal range for aquatic invertebrates (Delta C-13: 0.4 parts per thousand-4.1 parts per thousand and Delta N-15: 0.1 parts per thousand-5.3 parts per thousand). Overall, the turnover rates and discrimination factors for delta C-13 and delta N-15 indicated that C. gigas larvae assimilate C. calcitrans and PTC best under hatchery rearing conditions. The results demonstrated the application potential of stable isotope analysis to evaluate optimal diets and feeding regimes to enhance hatchery performance of bivalve larvae and postlarval stages.