The protein requirements, meaning the minimum amount needed to meet the requirements for amino acids and to achieve maximum growth, have now been measured in juvenile fish of many species (Table 1). They have been obtained mainly from dose-response curves in which graded amounts of high-quality protein were fed in partially defined diets. The response measured was weight gain. The values are expressed as a percentage of dry diet. Although the expression of protein as a proportion of dietary energy would have focused attention on protein as a substantial source of dietary energy, this approach was not possible for many of the studies because information on the digestible energy (DE) content of the diets was unavailable and values used for the energy composition of dietary components varied between authors. Many studies have been carried out to determine protein requirements for fish, with estimated protein requirements ranging from 30% to 55% according to fish species, size, dietary protein sources and environmental conditions