An experimental study of the reproductive behaviour and success of farmed and wild Atlantic salmon (Salmo salar).
Experiments were performed to assess the competitive and reproductive abilities of 5th-generation farmed salmon and their potential effects on populations of wild salmon. Mixed groups of wild and farmed salmon were held in outdoor areas with water flow and other features simulating a natural spawning area. The farmed and wild females showed similar levels of aggressive and submissive behaviour. However, compared with wild females, farmed females displayed less breeding behaviour, constructed fewer nests, retained a greater weight of eggs unspawned, were less efficient at nest covering, incurred more nest destruction, and suffered greater egg mortality. As a result, farmed females had less than one-third of the reproductive success of wild females. The farmed males were even less successful than the farmed females in competition with the wild fish. They were less aggressive, courted less, took part in fewer spawnings, and achieved only an estimated 1-3% of the reproductive success of the wild males. Farmed males exhibited inappropriate mating behaviour that led to poor fertilization success, even in the absence of competition with wild males. It was concluded that farmed fish are likely to be relatively unsuccessful in natural environments due to a competitive and reproductive inferiority apparently resulting from domestication.