Physiological, behavioural and pathological effects of sea lice, Lepeophtheirus salmonis (Krøyer, 1837), on Salmonids

This thesis examined the physiological, behavioural and pathological effects of sea lice, Lepeophtheirus salmonis (Krøyer, 1837), on wild sea trout, Salmo trutta L., and experimentally infected sea trout and Atlantic salmon, Salmo salar L. to determine how, and to what extent, sea lice cause mortality of their infected hosts. A feeding hierarchy was established in groups of sea lice infected and uninfected Atlantic salmon as a physiological stressor. Results indicated that chalimus did not stimulate physiological changes leading to marine mortality and the intensity of the sea lice infection on a fish was independent of that individual's food consumption. However, preadult stages caused appetite suppression, severe skin lesions and changes in the blood biochemistry of the fish with subsequent recovery to the levels of uninfected fish as the parasite moulted through to the adult stages of the lifecycle. The effects of sea lice on sea trout at either 2 or 6 weeks after sea water transfer were assessed. Both infection intensity and developmental rate were not significantly different between the groups, but a trend of fewer lice on the fish infected 6 weeks after sea water transfer was recorded. Fewer of the fish infected 2 weeks after sea water transfer had resumed feeding by the end of the experiment, leading to a loss of body condition, and suffered more severe damage to the skin and detrimental changes in the physiological integrity as a consequence of feeding preadult lice. The mortal impact of sea lice infection was significantly enhanced in the fish infected 2 weeks after sea water transfer. The findings from this thesis have shown that preadult sea lice can cause mortality of wild and experimentally infected sea trout and Atlantic salmon, particularly if infected at the time of sea water transfer, but under certain conditions sea lice infected hosts can recover from the detrimental effects of both chalimus and mobile stages.