An epigenetic basis for transgenerational plasticity in animals is widely theorized, but convincing empirical support is limited by taxa-specific differences in the presence and role of epigenetic mechanisms. In teleost fishes, DNA methylation generally does not undergo extensive reprogramming and has been linked with environmentally-induced intergenerational effects, but solely in the context of early life environmental differences. Using whole genome bisulfite sequencing, we demonstrate that differential methylation of sperm occurs in response to captivity during the maturation of Atlantic Salmon (Salmo salar), a species of major economic and conservation significance. We show that adult captive exposure further induces differential methylation in an F1 generation that is associated with fitness-related phenotypic differences. Some genes targeted with differential methylation were consistent with genes differential methylated in other salmonid fishes experiencing early-life hatchery rearing, as well as genes under selection in domesticated species. Our results support a mechanism of transgenerational plasticity mediated by intergenerational inheritance of DNA methylation acquired late in life for salmon. To our knowledge, this is the first-time environmental variation experienced later in life has been directly demonstrated to influence gamete DNA methylation in fish.

An epigenetic basis for transgenerational plasticity is widely theorized but convincing empirical support is limited by taxa-specific differences in the presence and role of epigenetic mechanisms. In teleost fishes, DNA methylation does not undergo extensive reprogramming and has been linked with environmentally-induced intergenerational effects, but solely in the context of early life environmental differences. Using whole genome bisulfite sequencing, we demonstrate that differential methylation of sperm occurs in response to captivity during maturation for Atlantic Salmon (Salmo salar), a species of major economic and conservation significance. We show that adult captive exposure further induces differential methylation in an F1 generation that is associated with fitness-related phenotypic differences. Gene targets of differential methylation are consistent with salmonid fishes experiencing early-life hatchery rearing as well as targets of selection in domesticated species. Our results support a mechanism of transgenerational plasticity mediated by intergenerational inheritance of DNA methylation acquired late in life for salmon.

The Striped Bass Morone saxatilis is an apex predator that supports recreational, commercial, and First Nations traditional fisheries in the Miramichi River, New Brunswick, Canada. Historic exploitation resulted in steep population declines, forcing a complete fisheries moratorium in 2000. After 13 years of recovery, a recreational fishery was reopened (May 2013) followed by a commercial fishery in 2018. These new opportunities for harvesting raised concerns about mercury levels in fish for human consumption as past levels have exceeded Health Canada guidelines of 0.5 mg/kg. We collected Striped Bass from the northwest Miramichi River in spring during the main recreational and commercial fishing seasons. Fish in the legal harvest slot for the recreational (50-65 cm TL) and commercial (50-80 cm TL) fisheries had total mercury in muscle tissue ranging from 0.08 to 0.43 mg/kg and from 0.08 to 0.63 mg/kg wet weight, respectively. Mercury levels in Striped Bass have decreased since the 1990s, but some individuals were close to or exceeded consumption guidelines. In addition, a preliminary angler creel survey revealed that only 8% of anglers retained their legal, three-fish limit (average harvest = 0.7 fish/angler/day). However, harvest of oversized fish was observed (11%), and a removal of~100,000 adults in the first month of the fishery by the recreational, commercial, and Indigenous fisheries is possible and represents a significant portion of the estimated adult population. We conclude that effective management of the Striped Bass fishery in the Miramichi River will require continued and more detailed angler surveys and population size and structure assessments accompanied by communication of current mercury levels in this species.The Miramichi River in New Brunswick, Canada, has long hosted intensive industry, commercial fisheries, and recreational angling activities directly adjacent to key spawning and nursery habitat for numerous native anadromous and estuarine fishes (Philpott 1978). A major spawning assemblage of Striped Bass Morone saxatilis aggregates annually in the northwest (NW) branch of the Miramichi River (Douglas et al. 2009) where they were once harvested in directed commercial fisheries and for personal use by recreational anglers until both commercial sale and recreational retention were ended in March 1996 in response to population declines (Bradford and Chaput

The Morone saxatilis (Striped Bass) population in Saint John River (SJR), NB, Canada, collapsed in the 1970s concurrent with dam construction, overfishing, and chemical pollution that may have impeded reproduction. To assess whether a chemical threat to Striped Bass or a health threat to fish consumers persists, we examined DDT and total mercury (THg) levels from 29 Striped Bass captured in the SJR including 16 genomically typed as SJR natives. DDT and DDD in female gonads were below detectable levels, and DDE averaged 0.08 ± 0.09 mg/kg wet weight (ww) but was considered too low to threaten reproduction. Total mercury in muscle and liver varied from 0.68 to 2.10 mg/kg and 0.35 to 3.27 mg/kg ww, respectively and exceeded Health Canada guidelines in all samples. We suggest regulators should update advisories for consumption including actively informing the public of the risk.