The physiological effects of salmon lice (Lepeophtheirus salmonis) infections on returning post-smolt sea trout (Salmo trutta L.) in western Ireland, 1996

The physiological impact and pathological effect of salmon lice, Lepeophtheirus salmonis (Kroyer, 1837), on wild sea trout, Salmo trutta L., was investigated in 10 rivers in Western IreIand. No skin damage was apparent on fish with mobile pre-adult and adult lice, but severe fin erosion was recorded in many of the fish that were infected with chalimus stages. The attached copepodid and chalimus stages of the parasite did not reduce the physiological performance of the sea trout although there was a significant reduction in total protein, serum albumin and cholesterol in fish with mobile stages compared with fish with attached stages only and fish with no lice. This may reflect the feeding history of the fish, as most of the fish with mobile lice were from the same area, or the physiological effects of lice infections may be stage-specific. (C) 1998 International Council for the Exploration of the Sea.