Abstract
BackgroundIn fish, morphological colour changes occur from variations in pigment concentrations and in the morphology, density, and distribution of chromatophores in the skin. However, the underlying mechanisms remain unresolved in most species. Here, we describe the first investigation into the genetic and environmental basis of spot pattern development in one of the world’s most studied fishes, the Atlantic salmon. We reared 920 salmon from 64 families of domesticated, F1-hybrid and wild origin in two contrasting environments (Hatchery; tanks for the freshwater stage and sea cages for the marine stage, and River; a natural river for the freshwater stage and tanks for the marine stage). Fish were measured, photographed and spot patterns evaluated.ResultsIn the Hatchery experiment, significant but modest differences in spot density were observed among domesticated, F1-hybrid (1.4-fold spottier than domesticated) and wild salmon (1.7-fold spottier than domesticated). A heritability of 6% was calculated for spot density, and a significant QTL on linkage group SSA014 was detected. In the River experiment, significant but modest differences in spot density were also observed among domesticated, F1-hybrid (1.2-fold spottier than domesticated) and wild salmon (1.8-fold spottier than domesticated). Domesticated salmon were sevenfold spottier in the Hatchery vs. River experiment. While different wild populations were used for the two experiments, on average, these were 6.2-fold spottier in the Hatchery vs. River experiment. Fish in the Hatchery experiment displayed scattered to random spot patterns while fish in the River experiment displayed clustered spot patterns.ConclusionsThese data demonstrate that while genetics plays an underlying role, environmental variation represents the primary determinant of spot pattern development in Atlantic salmon.
Highlights
Morphological colour changes in fish occur from variations in pigment concentrations and in the morphology, density, and distribution of chromatophores in
Independently of genetic origin, clearly-visible differences in spot patterns between fish reared in the Hatchery and River experiments were observed (Fig. 4)
Environmental variation was clearly the primary determinant as fish of domesticated, wild-domesticated F1 hybrid and wild pedigree all displayed a six to sevenfold higher density of spots when reared under farming conditions (Hatchery experiment—fish tanks, sea cages), as opposed to a combination of the river and thereafter farming conditions (River experiment—natural river, fish tanks)
Summary
Morphological colour changes occur from variations in pigment concentrations and in the morphology, density, and distribution of chromatophores in the skin. Morphological colour changes in fish occur from variations in pigment concentrations and in the morphology, density, and distribution of chromatophores in. “spottiness” as it is commonly known, is often determined by polymorphisms in the melanocortin-1 receptor (MC1R) in vertebrates, and this receptor family is involved in regulating immunity and stress responses [3, 10]. The specific role of melanophores is to protect the skin from UV damage [10] In anadromous fish, such as Atlantic salmon (Salmo salar L.), plasticity of patterning is probably the consequence of ontogenic habitat shifts [12]. Life-stage skin colouration can be modulated in response to environmental factors, allowing finetuning of the ultimate patterns. Environmental factors can be primary when they have a direct effect on chromatophores, or they can be secondary, allowing further adjustment of colour during a life stage [2]
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