Several authors have shown that by feeding bivalve larvae on a mixed algal diet growth is often better than when each of the constituent species of the diet was fed individually (Davis & Guillard, 1958; Walne & Spencer, 1968; Calabrese & Davis, 1970). The criterion upon which the value of the diets has been assessed has almost invariably been larval growth and rarely have the larvae been grown to metamorphosis.

This paper reports the results of a series of trials with Ostrea edulis L. larvae which were fed with three diets. Two were single species diets of Isochrysis galbana Parke and Tetraselmis suecica (Kylin) Butch, while the third was a combination of these two species. Larvae were grown to metamorphosis on each of the diets and then for a further period with a common food to assess the value of the larval diet on the subsequent performance of the spat.