Presents 2 models of growth and reproduction in Mytilus edulis, one a modified version of a model developed by Kooijman for general application to ectotherms, the other is a new model specifically formulated for mussels. The models have identical assumptions on energy assimilation and spawning but differ in assumptions concerning energy partitioning between growth, maintenance and reproduction. Both models were successful in predicting growth and reproduction in the test populations, suggesting that differences between populations can largely be explained by differences in food and seston dynamics. The models yield 2 contrasting strategies for storing and utilizing assimilate, and with further assumptions yield hypotheses on mortality in fast and slow growing populations. -from Authors