Further studies on acquired resistance to amoebic gill disease (AGD) in Atlantic salmon, Salmo salar L

Trials were designed to test the efficacy of freshwater treatments for amoebic gill disease (AGD) of Atlantic salmon, Salmo salar L., and the effect they had on the acquisition of resistance to reinfection with AGD. The first trial involved fish being given an industry-simulated freshwater bath of 2-3 h duration which simulated treatments given on farms. These fish did not display appreciable resistance to reinfection. The second trial involved four groups of fish which had been infected with and treated for AGD in a number of different ways. Once again the fish that had been infected for the first time and given a single 2-3 h freshwater bath and then re-exposed did not exhibit appreciable resistance to reinfection. In contrast, those fish that had been given a second 2-3 h freshwater bath and those that had been maintained in freshwater for 4 weeks displayed high levels of resistance. There is preliminary evidence to suggest that this resistance could be related to stimulation of the non-specific immune system.