Improvements in modern commercial aquaculture are linked to the utilization of biotechnological methods and processes. The most visible approach has been the use of growth hormone (GH) and/or insulin-like growth factor I and II (IGF-I and II), to accelerate the growth of fish. Previously we have reported that the injection of bovine GH, (bGH) in striped bass hybrids increased the specific growth rate and food conversion efficiency without significant alteration of food consumption rate. In this paper we present the results of experiments in which growth, food consumption, conversion efficiency, ammonia excretion, and amino acid absorption were monitored for individual fish after bGH injection. The specific growth rate was stimulated by 50% without significant change in relative food consumption rate. Food conversion efficiency increased by 51%. Intestinal L-leucine absorption was increased by 25-40% at various concentrations tested. The relative N-retention was stimulated by 20% when computed raw. When a correction factor derived from the elevated amino acid absorption was introduced into the computations. the calculated relative N-retention was increased by 56%. Muscle amino acid profile was appreciably altered. We conclude GH supplementation or over-expression in aquaculture profoundly alters the physiological and nutritional conditions of fish. Nutritional profiles of fish food must be altered relative to these physiological changes in order to maximize growth.