Atlantic Salmon, Salmo Salar

Abstract

Farming of Atlantic salmon (Salmo salar) began in Norway in the late 1960s. During the 1980s and 1990s the production spread, mainly to other northwestern European countries and to Chile. In 1980 annual world production was less than 10,000 t and this increased to 850,000 t whole fish produced in 2000. It is projected to approach 2 million t in 2010. The growth rate of the fish in the farms is continuously improving, due to genetic selection, improved diets and feeding and improved management. The improvement in growth ascribed to genetic selection can be as much as 15–20% per generation if the salmon are from a combined family–phenotype selection programme (Gjedrem, 1983). Recent Canadian results have shown that transgenic salmon, which express growth hormone receptor activity in muscle tissues, have a growth rate 2.6–2.9 times that of the control population, mainly because of increased feed intake (Cook et al., 2000a). Selection or transgenic techniques may also influence the composition of the growth, result in improved feed conversion (Thodesen et al., 1999; Cook et al., 2000a) and change the rate of metabolism (Thodesen et al., 1999; Cook et al., 2000b,c). Economical feed conversions in Norwegian salmon farming have changed from more than 2 kg feed dry matter (DM) kg−1 gain in 1980 to approximately 1.15 kg kg−1 at the end of the 1990s. In salmon the biological feed conversion can vary from less than 0.6 to more than 1.3 kg intake kg−1 gain, and the proportion of protein and energy in diet partitioned into gain can vary from 25 to 60%, depending on the formulation of the diet and the size of the fish. Thus, requirement figures must be based on the requirements of the animal, related to growth, nutrient partitioning and the specific physiological processes in which the nutrient is required. Requirements differ throughout the life cycle. This is especially important in salmon, which undergo physiological changes during smoltification and transfer from a life in fresh water to salt water. In addition to developing the ability to maintain the ion balance in the hyperosmotic salt water, the salmon also