Contrasting effects of acute and chronic stress on the transcriptome, epigenome, and immune response of Atlantic salmon

Early-life stress can have long-lasting effects on immunity, but the underlying molecular mechanisms are unclear. We examined the effects of acute stress (cold-shock during embryogenesis) and chronic stress (absence of tank enrichment during larval-stage) on the gill transcriptome and methylome of Atlantic salmon four months post-hatch. While only chronic stress induced pronounced transcriptional effects, both acute and chronic stress caused lasting, and contrasting, changes in the methylome. Crucially, we also found that acute stress enhanced transcriptional response to an immunological challenge (lipopolysaccharide), but chronic stress suppressed this response. Our results suggest that epigenetic regulation may contribute to these effects on immuno-competence. Stress-induced changes in promoter or gene-body methylation were associated with altered expression of a small proportion of genes, and we also identified wider epigenetic regulation of signalling pathways involved in immune response. These findings have important implications for the management of stress and disease in wild and farmed fish.