SEA LICE (COPEPODA, CALIGIDAE) ON WILD SEA-TROUT (SALMO-TRUTTA L.) INSCOTLAND

Lepeophtheirus salmonis infection occurred on 30% of 622 sea trout exa mined from Scottish waters, with intensities up to 258 per fish. Calig us elongatus was rarer, being recorded on only 3% of trout, at a maxim um intensity of 14. Geographical and temporal variations were found in the pattern of infection with L. salmonis. Most lice recorded were ch alimus stages. On each fish, the same developmental stage of lice pred ominated, but this stage varied, even between fish caught on the same location at the same date. Haemorrhage at the base of dorsal fins infe cted with chalimus infection was the only skin damage found associated with lice. Analysis of the population structure of lice at two locati ons showed a progression of developmental stages with time, but also e vidence of continual re-infection up to the end of sampling in late Ju ly. A positive relationship was found between sea trout condition and the intensity of infection with chalimus III+ larvae but a negative re lationship was found with the intensity of chalimus II- infection, pos sibly related to the length of time in, and adaptation to, sea water. The heaviest infection of sea trout with lice was recorded in the salm on Farming areas of the west and north-west of Scotland. However, no c lear pattern emerged with levers of infection at single locations in r elation to the proximity to the nearest salmon farm or with the patter n of infection (and larval production) within an adjacent salmon farm. (C) 1998 International Council for the Exploration of the Sea.