Nutritional condition of rock scallop, Crassadoma gigantea (Gray), larvae fed mixed algal diets

Abstract

Larvae of C. gigantea were fed a binary diet of Isochrysis aff. galbana (T-iso) and Chaetoceros calcitrans, and two ternary diets consisting of the binary diet with either Tetraselmis suecica or Thalassiosira pseudonana. In a second feeding study, larvae were fed three ternary diets consisting of I. aff. galbana (T-iso) and C. calcitrans with either T. pseudonana, Chaetoceros gracilis or Skeletonema costatum. The biochemical composition, energy contents, and fatty acid compositions of the diets and resultant premetamorphic larvae were determined and compared, both within and between the studies. It was concluded that nutritional condition of the larvae correlated with the content of dietary carbohydrate rather than dietary lipid or protein. Differences in content of macronutrients in the diet, I. aff. galbana (T-iso), C. calcitrans and T. pseudonana, used in both feeding studies, resulted in substantial differences in nutritional condition of the premetamorphic larvae from the two studies. Determination of macronutrients in algal diets, even when the algae were cultured under conditions considered to be standard, was shown to be essential before any estimate of food value. Fatty acid composition of total lipid in the larvae reflected that of the diets, but levels of saturated, monoethylenic, polyethylenic, and polyunsaturated n3 or n6 fatty acids in the diets were not correlated with nutritional condition of the larvae. Accumulation of 16:0, 18:0, 18:1 n7, 20:5 n3, and 22:6 n3 fatty acids by the larvae, irrespective of diet supplied, suggested a need for these acids during larval growth and development. The importance of carbohydrate in providing a balanced diet for effective conversion of dietary macronutrients to tissue and energy reserves has hitherto been overlooked in larval nutrition.