NUTRITIONAL-VALUE OF ALGAL DIETS TO CLAM SPAT VENERUPIS-PULLASTRA

Clam spat Venerupis pullastra were fed for 4 wk on diets of 2 species of microalgae supplied singly or mixed. Microalgae were Isochrysis gal bana and Tetraselmis suecica, species normally used in bivalve hatcher ies. Observed growth responses were high for mixed and I. galbana diet s and intermediate for the T. suecica diet. A slightly higher growth r ate was obtained with the mixed diet than with the I. galbana diet. Di fferences in growth rate were explained by differences in rates of ing estion and digestibility and in the biochemical composition of diets. The intermediate growth rate for spat fed on T suecica was related to lower ingestion rates, lower assimilation efficiencies and lower dieta ry protein and lipid content. Spat biochemical composition was correla ted with growth indices. Lower growth indices were related to lower pr otein and higher lipid content of spat. The high growth response to th e mixed diet was not explained by the factors considered.