Biochemical and energy changes during embryogenesis in the rock scallopCrassadoma gigantea

Abstract

The biochemical composition of eggs spawned from rock scallopsCrassadoma gigantea (Gray) collected from Clayoquot Sound, Vancouver Island (British Columbia, Canada) in the winter of 1987 and the summer of 1988, differed significantly only in lipid and soluble-ash contents. Major macronutrients were catabolized simultaneously and linearly with time of embryogenesis. Total egg energy expended during development was 11.8 kJ g−1 derived 46.7, 9.8 and 43.5%, from lipid, carbohydrate, and protein, respectively. Glucose in the egg was the dominant source of carbohydrate energy. Deposition of shell was linear with time of embryogenesis and the formation of 44.8% dry wt of shell in the early larval stage, referred to as the D-larva, consumed 64.4% of the total energy expended. Energy required for shell formation was 17.55 kJ g−1. The RNA:DNA ratio declined exponentially from 18.6 in the egg to 2.21 in the D-larva, which was consistent with that of adult bivalves. Many changes in fatty acid composition were linear with time of embryogenesis, and the percentage ofn3- andn6-higher unsaturated fatty acids to total polyethylenic acids exhibited significant declining and increasing trends, respectively. The linear rate of catabolism of eicosapentaenoic acid, 20:5n3, and the constant level of docosahexaenoic acid, 22:6n3, illustrated an energy and a structural role, respectively, for these dominant acids in the embryonic development of the rock scallop.