Possible genetic interactions between reared strains and wild populations of cod (Gadus morhua): lessons from salmon (Salmo salar) common garden field experiments

No abstracts are to be cited without prior reference to the author.

With the increase in production from cod (Gadus morhua) farming and ranching around the North Atlantic, concern has been raised about detrimental effects of accidental or deliberate introductions of reared strains into the wild. Here we concentrate on the possible genetic effects of interactions of captive bred fish with wild conspecifics by extrapolating from the major findings of Irish field experiments with reared and wild Atlantic salmon Salmo salar. We then discuss the likelihood of similar effects being observed in cod. In the case of S. salar in a “common garden” scenario in a natural freshwater stream, native wild populations were found in many situations, simulating both farm escapes and stocking, to have significantly higher lifetime reproductive success (LRS) than their reared counterparts. Where wild X reared hybrids were produced LRS was lower depending on the extent of reared involvement (e.g. wild backcrosses more fit than F2 hybrids). The role of MHC in determining the fitness of introduced individuals was also demonstrated and suggested a high degree of local adaptation in salmon populations.