Does density influence relative growth performance of farm, wild and F1 hybrid Atlantic salmon in semi-natural and hatchery common garden conditions?

Alison C. Harvey,Ivar-Helge Matre,Gareth Juleff,Martin I. Taylor,Simon Creer,Kevin A. Glover,Monica F. Solberg,Lise Dyrhovden,Gary R. Carvalho

doi:10.1098/rsos.160152

Abstract

The conditions encountered by Atlantic salmon, Salmo salar L., in aquaculture are markedly different from the natural environment. Typically, farmed salmon experience much higher densities than wild individuals, and may therefore have adapted to living in high densities. Previous studies have demonstrated that farmed salmon typically outgrow wild salmon by large ratios in the hatchery, but these differences are much less pronounced in the wild. Such divergence in growth may be explained partly by the offspring of wild salmon experiencing higher stress and thus lower growth when compared under high-density farming conditions. Here, growth of farmed, wild and F1 hybrid salmon was studied at contrasting densities within a hatchery and semi-natural environment. Farmed salmon significantly outgrew hybrid and wild salmon in all treatments. Importantly, however, the reaction norms were similar across treatments for all groups. Thus, this study was unable to find evidence that the offspring of farmed salmon have adapted more readily to higher fish densities than wild salmon as a result of domestication. It is suggested that the substantially higher growth rate of farmed salmon observed in the hatchery compared with wild individuals may not solely be caused by differences in their ability to grow in high-density hatchery scenarios.

Highlights

Captive populations undergo various morphological, physiological and behavioural changes during domestication [1]
Growth of all three genetic groups decreased as density increased, with the lowest growth observed in the high-density hatchery treatment, the difference in growth between the hatchery treatments was not significant
It was hypothesized that farmed salmon may be able to maintain higher growth than their wild conspecifics in high-density environments, potentially explaining the elevated growth differences observed between wild 600 hybrid farm

Summary

Introduction

Captive populations undergo various morphological, physiological and behavioural changes during domestication [1]. Adaptation to the domestic environment occurs through two routes: environmentally induced changes to developmental processes within a single generation and genetic change across generations [2,3]. Relaxed natural selection can result in domestic individuals that are more variable than wild conspecifics for certain traits that have adaptive value in the wild but less so in captivity [4]. Genetic and morphological change occurs through direct and indirect responses to artificial selection and natural selection within the domestic environment contrasted with the wild environment (local adaptation in wild populations), and the differential mortality described above [2,5,6]. Many domestic populations have become adapted to their captive environment, and may have reduced fitness in natural or novel environments when compared with wild individuals [3,4]. A loss of adaptive potential through domestication can negatively influence wild populations if domesticated individuals interbreed with wild conspecifics, such as when farmed individuals are released for restocking or are accidentally released through escape events

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