THE USE OF CLEANER-FISH TO CONTROL SEA LICE ON 2 IRISH SALMON (SALMO-SALAR) FARMS WITH PARTICULAR REFERENCE TO WRASSE BEHAVIOR IN SALMON CAGES

Corkwing (Crenilabrus melops (L.)) and goldsinny (Ctenolabrus rupestri s (L.)) wrasse successfully controlled sea lice infestations on farmed Atlantic salmon smelts (Salmo salar L.) on two commercial fish farms off the west Irish coast, Lice levels were generally maintained below five mobile stages per fish using ratios as low as one wrasse to 250 s almon, and cleaner-fish were shown to be a more effective lice control method than conventional chemical treatments in the case of diseased or stressed salmon. High wrasse losses were recorded from cages, presu mably a result of escaping through the nets, or by smaller individuals being consumed by large smelts, Aggressive behaviour of smelts toward s the wrasse was observed when the cleaner-fish were first introduced to the cages. Cleaning behaviour was observed throughout the day thoug h a peak in cleaning activity was recorded in the early morning for co rkwing and at mid-day in the case of goldsinny, Specialist cleaners we re recorded by SCUBA observations and by gut content analysis, with up to 58 lice consumed by individual wrasse, Cleaning behaviour was enco uraged by maintaining clean nets, so limiting alternative food sources for the wrasse. Artificial shelters were utilized by both species, pa rticularly goldsinny, and some evidence of competition for resting spa ces was observed at dusk. A decline in cleaning activity was observed in October, probably a result of lower temperatures and reduced daylen gth. The results are discussed with regard to wrasse husbandry in the salmon cages.