title: Plasticity in growth of farmed and wild Atlantic salmon: is the increased growth rate of farmed salmon caused by evolutionary adaptations to the commercial diet?
abstract: Domestication of Atlantic salmon for commercial aquaculture has resulted in farmed salmon displaying substantially higher growth rates than wild salmon under farming conditions. In contrast, growth differences between farmed and wild salmon are much smaller when compared in the wild. The mechanisms underlying this contrast between environments remain largely unknown. It is possible that farmed salmon have adapted to the high-energy pellets developed specifically for aquaculture, contributing to inflated growth differences when fed on this diet. We studied growth and survival of 15 families of farmed, wild and F1 hybrid salmon fed three contrasting diets under hatchery conditions; a commercial salmon pellet diet, a commercial carp pellet diet, and a mixed natural diet consisting of preserved invertebrates commonly found in Norwegian rivers.
  
  
  
  For all groups, despite equal numbers of calories presented by all diets, overall growth reductions as high 68 and 83%, relative to the salmon diet was observed in the carp and natural diet treatments, respectively. Farmed salmon outgrew hybrid (intermediate) and wild salmon in all treatments. The relative growth difference between wild and farmed fish was highest in the carp diet (1: 2.1), intermediate in the salmon diet (1:1.9) and lowest in the natural diet (1:1.6). However, this trend was non-significant, and all groups displayed similar growth reaction norms and plasticity towards differing diets across the treatments.
  
  
  
  No indication of genetic-based adaptation to the form or nutritional content of commercial salmon diets was detected in the farmed salmon. Therefore, we conclude that diet alone, at least in the absence of other environmental stressors, is not the primary cause for the large contrast in growth differences between farmed and wild salmon in the hatchery and wild. Additionally, we conclude that genetically-increased appetite is likely to be the primary reason why farmed salmon display higher growth rates than wild salmon when fed ad lib rations under hatchery conditions. Our results contribute towards an understanding of the potential genetic changes that have occurred in farmed salmon in response to domestication, and the potential mechanisms underpinning genetic and ecological interactions between farmed escapees and wild salmonids.
authors.affiliation: Molecular Ecology and Fisheries Genetics Laboratory, School of Biological Sciences, Deiniol Road, Bangor University, Bangor, LL57 2UW, UK.
authors.forename: Alison Catherine
authors.initials: AC
authors.lastname: Harvey
authors.affiliation: Institute of Marine Research, P.O. Box 1870, Nordnes, NO-5817, Bergen, Norway. monica.solberg@imr.no.
authors.forename: Monica Favnebøe
authors.initials: MF
authors.lastname: Solberg
authors.affiliation: Institute of Marine Research, P.O. Box 1870, Nordnes, NO-5817, Bergen, Norway.
authors.forename: Eva
authors.initials: E
authors.lastname: Troianou
authors.affiliation: Molecular Ecology and Fisheries Genetics Laboratory, School of Biological Sciences, Deiniol Road, Bangor University, Bangor, LL57 2UW, UK.
authors.forename: Gary Robert
authors.initials: GR
authors.lastname: Carvalho
authors.affiliation: School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich, UK.
authors.forename: Martin Ian
authors.initials: MI
authors.lastname: Taylor
authors.affiliation: Molecular Ecology and Fisheries Genetics Laboratory, School of Biological Sciences, Deiniol Road, Bangor University, Bangor, LL57 2UW, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Creer
authors.affiliation: Institute of Marine Research, P.O. Box 1870, Nordnes, NO-5817, Bergen, Norway.
authors.forename: Lise
authors.initials: L
authors.lastname: Dyrhovden
authors.affiliation: Institute of Marine Research, P.O. Box 1870, Nordnes, NO-5817, Bergen, Norway.
authors.forename: Ivar Helge
authors.initials: IH
authors.lastname: Matre
authors.affiliation: Institute of Marine Research, P.O. Box 1870, Nordnes, NO-5817, Bergen, Norway.|Sea Lice Research Centre, Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: Kevin Alan
authors.initials: KA
authors.lastname: Glover
mesh_terms: D000220:Adaptation, Biological; D000821:Animal Feed; D000818:Animals; D017756:Aquaculture; D005075:Biological Evolution; D049628:Body Size; D004032:Diet; D000072480:Farms; D005247:Feeding Behavior; D005260:Female; D008297:Male; D045483:Rivers; D020317:Salmo salar / Q000254:growth & development*
keywords: Appetite; Domestication; Farm escapes; Feed utilisation; Genetic interaction; Hybridisation; Natural diet; Pellets; Reaction norms; Salmonids; Survival