Interactive effects of temperature and food ration on growth and mercury concentration in Eastern Brook Trout

Warming temperatures predicted under global climate change will alter the dynamics of secondary production and trace element accumulation and interact with environmental factors such as food resource availability to influence both growth and bioaccumulation. We conducted laboratory experiments to assess the role of temperature and food ration on brook trout (a cold-water-dependent fish) growth and mercury (Hg) concentration. Across a range of temperatures (15–24 °C), brook trout growth rate decreased and Hg concentration increased with temperature. We observed the lowest Hg concentrations in fish under the low temperature (15 °C), high ration treatment, and highest concentrations in the high temperature (22 °C), zero ration treatment. Relative growth rank of individual fish was a significant predictor of Hg concentration, with fast-growing individuals having lower Hg. Based on structural equation modelling, the strongest relationship between Hg in brook trout muscle tissue and the temperature/ration treatments was through an indirect pathway mediated by brook trout growth rate. Our results provide support for a link between warming temperatures, growth, and bioaccumulation rates in upland stream food webs, with implications for wildlife and human health.