Meeting Abstract

S2.5  Sunday, Jan. 4  Salmon Lice Infection of Farmed and Wild Salmonids in Norway: an Overview HEUCH, P.A.*; BJORN, P.A.; FINSTAD, B.; ASPLIN, L.; HOLST, J.C.; National Veterinary Institute, Oslo, Norway; Norwegian Institute for Fisheries and Aquaculture Research, Tromso; Norwegian Institute for Nature Research, Trondheim; Institute for Marine Research, Bergen, Norway; Institute for Marine Research, Bergen, Norway peter-andreas.heuch@vetinst.no

Salmon lice Lepeophtheirus salmonis have three wild host species in Norway: Atlantic salmon Salmo salar, sea trout S. trutta and Arctic charr Salvelinus alpinus, all of which leave the rivers in spring. The parasite infects the marine stages of these fish. In addition, 273 million farmed Atlantic salmon and rainbow trout Oncorhynchus mykiss hosts are kept in open net pens along the coast. Regulations require that adult female lice mean intensity on these must be <0.5 to limit infection of the wild salmonids, but heavily infected wild fish are still found in farming areas. Infection dynamics depend on local host ecology, hydrography and lice control in farms. In a 1998-2004 study, salmon smolts in the far North Alta fjord were seen to run before the other wild hosts, and were hardly infected. Sea trout smolts here run later but can get heavy infections even though the production of lice in farms is very low. In the Southern Sognefjord, salmon smolt infections were high until the fish farm regulations were in operation in 2004, when they were much lower, but also here the sea trout infections have remained high. In the neighbouring Hardanger fjord, farmers have organized strategic treatments in winter, with the aim of no egg-producing lice on farmed fish in spring. This has lead to a very low lice abundance on farmed fish, but wild salmonids are some years heavily infected. This paper summarizes research on the interactions between biotic and abiotic factors with respect to salmon lice infections, and discusses new strategies for lice control in farms.