The behaviour of Atlantic salmon in relation to efficient cage-rearing

To maintain salmon farming as a viable industry it is necessary to continue to focus on the well-being of the fish from hatching to harvesting. This requires intimate knowledge of all aspects of salmon biology. Understanding the behaviour of farmed salmon is an essential part as this could suggest ways of preventing stress and diseases rather than merely treating their symptoms. This review attempts to summarize current knowledge of salmon behaviour in sea cages. Major modes of behaviour have been described and possible control mechanisms have been suggested. Behavioural studies of salmon in this particular system, however, are still at an early stage. Further research is needed to verify and deepen the current understanding. In future research the behavioural ontogeny of cultured salmon from hatching to harvesting should receive more attention. For example, the effect of smolt-rearing procedures on subsequent behaviour in sea cages is unclear. An ontogenetic approach would probably pay off in terms of a better holistic understanding of the mechanisms controlling the behaviour of cultured salmon in different stages of the production process.The present level of understanding should provide a basis for developing simple models of behaviour in cages from which meaningful hypotheses can be formulated. Experiments should primarily be carried out in a realistic rearing environment, but the inherent methodological problems of carrying out full-scale experiments make it difficult to test hypotheses that require detailed description of the behaviour of individuals. The transfer of a small number of individuals from larger groups subjected to different treatments to an experimental arena, might overcome these problems. This approach proved fruitful in an unpublished study that tested the competitive ability of individuals reared under different feeding regimes.