Evaluation of live microalgal diets for the seed culture of Ruditapes decussatus using physiological and biochemical parameters

The nutritional quality of several microalgal diets used in the seed culture of the little-neck clam, Ruditapes decussatus, was evaluated in the present study. The live diets tested were Isochrysis galbana, clone T-ISO, Tetraselmis suecica and Phaeodactylum tricornutum. Criteria used in the evaluation of the diets were acceptability, digestibility, growth and biochemical composition. The highest growth rate was registered in the seed fed the T. suecica diet, followed by the seed fed I. galbana, while the lowest one was obtained in the seed fed P. tricornutum. Food ingestion rates were higher in the seed fed Tetraselmis. This fact would partly explain the higher growth observed with this diet, The limited nutritional value of Phaeodactylum could be related to the low digestibility of its cell wall, the degree of acceptability of this diet being similar to or even higher than that of the other two. The low protein content of Tetraselmis seems to indicate that R. decussatus shows a low requirement for proteins, which can be spared by carbohydrate, an abundant component in the cells of Tetraselmis. Lipid needs of this bivalve also seem to be rather low.