© 2006 International Council for the Exploration of the Sea
Temporal variation in an immune response gene (MHC I) in anadromous Salmo trutta in an Irish river before and during aquaculture activities
a Department of Zoology, Ecology and Plant Science/Aquaculture and Fisheries Development Centre, Environmental Research Institute, National University of Ireland Cork, Ireland
b Marine Institute, Catchment Management and Aquaculture Services Newport, County Mayo, Ireland
c Norwegian Institute for Nature Research 7485 Trondheim, Norway
d Scottish Fish Immunology Research Centre, University of Aberdeen Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland, UK
*Correspondence to T. F. Cross: tel: +353 21 4904652; fax: +353 21 4904664. e-mail: t.cross{at}ucc.ie.
Several studies have documented the genetic effects of intraspecific hybridization of cultured and wild Atlantic salmon (Salmo salar L.). However, the effect of salmon aquaculture on wild congeners is not so well understood. Diseases, introduced or increased in incidence by salmon aquaculture activities, may have an impact on co-occurring wild sea trout (Salmo trutta L.), as implied by the steep decline in sea trout numbers in many Irish, Scottish, and Norwegian rivers since the late 1980s, which may be linked to sea lice infestations associated with marine salmonid farming. Our data suggest that salmon farming and ocean ranching can indirectly affect, most likely mediated by disease, the genetics of cohabiting sea trout by reducing variability at major histocompatibility class I genes. We studied samples of DNA extracted from scales of sea trout in the Burrishoole River, in the west of Ireland, before and at intervals during aquaculture activities. In these samples, allelic variation at a microsatellite marker, tightly linked to a locus critical to immune response (Satr-UBA), was compared with variation at six neutral microsatellite loci. A significant decline in allelic richness and gene diversity at the Satr-UBA marker locus, observed since aquaculture started and which may indicate a selective response, was not reflected by similar reductions at neutral loci. Subsequent recovery of variability at the Satr-UBA marker, seen among later samples, may reflect an increased contribution by resident brown trout to the remaining sea trout stock.
Keywords: MHC, microsatellites, Salmo trutta, sea trout, temporal variation
Received 11 November 2005; accepted 31 March 2006.