Growth Rates and Nitrogen and Carbohydrate Contents of Juvenile Clams, Saxidomus giganteus, Fed Three Species of Algae

Abstract

Estimates were made of the increase in live and dry weights and in the content of ash, organic matter, carbohydrate (as glucose), and nitrogen when juveniles of the clam Saxidomus giganteus were fed for 21 days at various concentrations of Tetraselmis chui, Isochrysis galbana, and Phaeodactylum tricornutum. The condition index (organic weight as a percent of total dry weight) increased in all the experimental conditions with a mixture of I. galbana and T. chui, yielding a significantly higher index than either species on its own. The relative gain in glucose was greater than the increase in live weight or in nitrogen. The increase in live weight was such that the nigrogen content was approximately constant at 6–7 μgN/mg live weight irrespective of the feeding conditions. The N:glucose ratio decreased with increasing concentrations of I. galbana and P. tricornutum, and at the higher concentrations, where the maximum growth rate of clams occurred, the ratios were lower than in any of the clams fed on T. chui.