Environmental enrichment during early rearing provokes epigenetic changes in the brain of a salmonid fish

Environmental enrichment is used to increase structural complexity of captive rearing systems and has been shown to provoke a wide range of effects in the kept animals. Here we studied the effects of enrichment on DNA methylation patterns at the whole-genome level in the brain of rainbow trout reared in an aquaculture setting. We investigated the epigenetic effects between different types of enrichment (natural substrate vs. artificial substrate vs. barren) in three developmental stages (egg vs. alevin vs. fry) and as enrichment was discontinued at the fingerling stage by means of the Methylation-Sensitive Amplified Polymorphism (MSAP) technique. While enrichment did not affect growth in body size, we found enrichment to affected global DNA methylation in the brain at the egg and alevin stage, i.e., the period during development where the animals are in close physical contact with the substrate. At these stages, trout reared on the two substrates differed more from the control than the substrates differed from each other. Only minor differences between rearing environments were detected following emergence at the fry stage. When enrichment was discontinued during the rearing of fingerlings, no differences in DNA methylation patterns were observed between the rearing environments. Our results provide further evidence on the effects of enrichment in the captive rearing of fish and show that enrichment can even modulate epigenetic patterns. The effect on the epigenome may be causal for the previously reported effects of enrichment on gene expression, behaviour and brain development.