Relations between variable rates of growth, metabolic costs and growth efficiencies in individual Sydney rock oysters (Saccostrea commercialis)

Rock oysters from a mass selection trial were compared with wild-caught (co ntrol) oysters of the same age to determine the physiological basis for fas ter growth rates amongst the selected individuals, and to describe the asso ciated flexibility in phenotypic traits of feeding, metabolism and growth. In confirmation of earlier studies, fast growth was associated with faster rates of feeding, reduced metabolic rates and lower metabolic costs of grow th. Selected individuals deposited more protein, at a lower metabolic cost, than the controls. Control oysters, however, deposited more lipid than the selected oysters, though the unit costs of lipid deposition did not differ between categories. The results indicated a wide plasticity of physiologic al rates and efficiencies and demonstrated how, by selection, interactions between physiological traits can serve to enhance growth. If differences in lipid deposition observed here were indicative of different rates of gamet ogenesis, then the results also suggest that selection alters the balance b etween growth and reproduction. Whether these differences can be termed com pensatory with respect to the life history of the species remains to be det ermined, but the results indicate some of the ways in which physiological f lexibility may be expressed to effect different patterns of energy allocati on. (C) 2000 Elsevier Science B.V. All rights reserved.