The relationship between gross biochemical composition of cultured algal foods and growth of the hard clam, Mercenaria mercenaria (L.)

Abstract

Under controlled laboratory conditions, young, post-set hard clams, Mercenaria mercenaria (L.), were reared for at least 12 weeks on 19 axenically-cultured unialgal diets; unfed controls were included. Daily algal rations were adjusted to have equivalent packed cell volumes but varied considerably in cell number (inversely related to cell size), dry weight, protein, lipid, and carbohydrate. Growth rates of hard clams fed experimental diets were calculated from weekly live-weight determinations; large differences in clam growth were observed. Of all algal ration characteristics measured, protein and lipid were the only two to show significant correlations (Spearman rank procedure, P < 0.05) with clam growth rate. A multiple linear regression model relating dietary protein, lipid, and carbohydrate with clam growth rate was highly significant ( P < 0.0001), and explained 69% of the differences in clam growth on the 19 algal diets. Three algal species were cultured in different media to alter gross biochemical composition; results of feeding these algal strains confirmed that both dietary protein and lipid must be present in sufficient quantities to support rapid growth of hard clams. These findings have direct application to experimental and commercial clam rearing, and also further our understanding of the role of nutrition in population biology of clams in the field.