Nutritional value of algal diets to clam spat

Clam spat Venerupis pullastra were fed for 4 wk on &ets of 2 species of microalgae supplied singly or mixed. Microalgae were Isochrysis galbana and Tetraselmis suecica, species normally used in bivalve hatcheries. Observed growth responses were high for mixed and I. galbana diets and intermediate for the T suecica diet. A slightly higher growth rate was obtained with the mixed diet than with the I. galbana diet. Differences in growth rate were explained by differences in rates of ingestion and digestibility and in the biochemical composition of diets. The intermediate growth rate for spat fed on T. suecjca was related to lower ingestion rates, lower assimilation efficiencies and lower dietary protein and lipid content. Spat biochemical composition was correlated with growth indices. Lower growth indices were related to lower protein and higher lipid content of spat. The high growth response to the mixed diet was not explained by the factors considered.