Feed conversion ratio (FCR) is calculated from the number of kilograms of feed that are used to produce one kilogram of whole fish. According to the Federation of European Aquaculture Producers, FCR is the ratio of the gain in the wet body weight of the fish to the amount of feed fed. The ratio, usually expressed as a true ratio (i.e. 1 : 1.5) is often quoted as a “rate” (1.5). Feed conversion ratios of less than 1 : 1 are possible with commercial diets, as the pellet being fed is a “dry” diet, and a high per cent of weight gained by the fish, is water trapped in the tissues and cells. Feed conversion ratios with commercial “dry” diets are typically in the region of 1 : 0.8 to 1 : 1.5. Two additional terms are used by the farmer, the biological FCR and the economic FCR. Biological FCR is the net amount of feed used to produce one kg of fish, while the economic FCR takes into account all the feed used, meaning that the effects of feed losses and mortalities, for example, are included. F