No abstract

Cutting-edge DNA methylation-based epigenetic aging techniques were applied to Gulf of Mexico northern red snapper (Lutjanus campechanus; n = 10; 1–26 years old) and red grouper (Epinephelus morio; n = 10; 2–14 years old). Bisulfite-converted restriction site-associated DNA sequencing was used to identify CpG sites (cytosines followed by guanines) that exhibit age-correlated DNA methylation, and species-specific epigenetic clocks developed from 100s of CpG sites in each species showed strong agreements between predicted and otolith-derived ages (r2 > 0.99 for both species). Results suggest epigenetic age estimation could provide an accurate and efficient approach to mass-aging fishes in a non-invasive manner.

Pacific salmon (Oncoryhnchus spp.) and brown trout (Salmo trutta) are introduced species stocked in the Laurentian Great Lakes. In their native range, salmon deliver material that enhances growth, alters isotopic ratios, and increases contaminant burdens of resident fish. However, whether salmon subsidies mediate interactions between competing species is unknown. Here, we employed a mesocosm experiment and a simulation model to determine if salmon tissue consumption influences brook trout (Salvelinus fontinalis) growth, isotopic ratios, and mercury concentrations and whether these were modified by brown trout. Our results indicate that brook trout growth did not increase with provision of salmon tissue and was not reduced by brown trout. However, brook trout exhibited isotopic enrichment and increased mercury concentrations, suggesting dietary intake of salmon tissue. Because salmon eggs have a higher energy density and lower mercury concentration compared with salmon tissue, our simulation model suggests that consumption of salmon eggs rather than tissue can increase growth while reducing mercury accumulation. Overall, our results suggest that the role of introduced Pacific salmon is dependent on both food quantity and quality along with diet contaminant concentrations.

A suite of blood chemistry parameters (including acid–base indicators and plasma electrolytes) was serially measured in blacktip sharks (Carcharhinus limbatus), captured via rod-and-reel, to gain a more thorough understanding of the physiological stress response to recreational capture. Sharks were caught both from the shore and from fishing vessels and experienced varying degrees of air exposure during handling. While all captured sharks exhibited a metabolic acidosis during the fight on the line (increasing lactate and decreasing pH and bicarbonate), the observed acidosis was compounded by a respiratory component (increasing pCO2) in sharks removed from the water during handling. Vessel-caught sharks handled in the water exhibited significantly greater increases in lactate and glucose (0.73 ± 0.21 mmoll−1 min−1 and 0.81 ± 1.07 mg dl−1 min−1, respectively) than sharks handled out of water (0.21 ± 0.17 mmoll−1 min−1 and −0.32 ± 1.05 mg dl−1 min−1; p < 0.001 and p < 0.05, respectively). These findings provide insights into how differences in recreational capture methods and air exposure can mediate the origin and magnitude of capture-related stress and highlight the importance of considering both sampling time (time from capture to phlebotomy) and sampling location (in water vs. out) in studies conducted on capture-related stress.