Data from: 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?

Background: 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. Results:
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. Conclusions: 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.