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ABSTRACT. Atlantic salmon Salmo salar L. artificially infected with salmon lice Lepeophtheirus salmonis (Krpryer 1837) recovered from detrimental physiological changes and skin damage induced by preadult lice as the parasites matured. Growth rates of Atlantic salmon remained unaffected by lice infection, but food consumption decreased wlth increasing feeding and movement of the lice prior to and post-mating, correlating with the appearance of head erosions and detr~mental changes in physiological integrity. Food consumption of the fish increased as the lice moulted to the adult stage and gravid female lice settled in a posterior location on the fish, subsequently reducing the impact of infection and allowing recovery of the skin damage. However, the impact of preadults was limited, as the decrease in food consumption of fish at 21 d post-infection had no effect on either the specific growth rate or condition factor of the flsh. Furthermore, the intensity of lice infections at each of the sample days was not correlated with food consumption, specific growth rate or any of the haematological or physiological parameters measured, either before or after infection, indicating that lice intensity was independent of social dorninance/subordinance. This work has provided the first evidence that infected fish can recover from the detrimental changes caused by lice infection, even when they are still infected with lice. If fish can survive the preadult stage of lice, then the mortal impact of lice infections is greatly reduced.

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The physiological and behavioural effects and skin damage caused by salmon lice Lepeophtheirus salrnonis (Kreyer) infections on sea trout Salmo trutta L. smolts were greater in fish infected with lice 2 wk after seawater transfer than in fish infected 6 w k after seawater transfer. The initial prevalence of infection was 100% for both groups and the intensity of infection decreased significantly with time over 5 wk. Significantly fewer of the fish infected 2 wk after seawater transfer had resumed feeding by the end of the experiment, leading to a loss of body condition. Furthermore, these fish suffered more severe damage to the skin and detrimental changes in physiological integrity than fish infected 6 wk after seawater transfer as a direct consequence of feeding preadult lice, leading to osmoregulatory failure and death. Although this study was carried out in laboratory conditions, results indicate that lice infections may potentially have a detrimental impact on the survival of wild smolts after seawater transfer