Physiological components of growth differences between individual oysters (Crassostrea gigas) and a comparison with Saccostrea commercialis

Pacific oysters (Crassostera gigas) of identical age from two genetically d istinct lines, one fast growing and the other slow growing, were held at th ree levels of ration and analysed for physiological traits to explain diffe rences in their rates of growth. The data supported three hypotheses; faste r growth was associated with faster rates of consumption of food, reduced m etabolic rate at maintenance (i.e., at zero growth), and reduced metabolic costs of growth. A comparison with the Sydney rock oyster, Saccostrea comme rcialis, based on similar experiments on the two species, indicated that fa ster growth of Pacific oysters depended on similar physiological difference s; the mean metabolic costs of growth, however, were similar in the two spe cies. It is suggested that a general model for genetically linked differenc es in the growth rate of bivalve molluscs will need to include the processe s of metabolic control rather than relying solely on an analysis of the ind ividual components of the energetics of growth.