J.M. Lepak | USGS Science

USGS2012

The influence of external subsidies on diet, growth and Hg concentrations of freshwater sport fish: implications for management and fish consumption advisories

Mercury (Hg) contamination in sport fish is a global problem. In freshwater systems, food web structure, sport fish sex, size, diet and growth rates influence Hg bioaccumulation. Fish stocking is a common management practice worldwide that can introduce external energy and contaminants into freshwater systems. Thus, stocking can alter many of the factors that influence Hg concentrations in sport fish. Here we evaluated the influence of external subsidies, in the form of hatchery-raised rainbow trout Oncorhynchus mykiss on walleye Sander vitreus diet, growth and Hg concentrations in two freshwater systems. Stocking differentially influenced male and female walleye diets and growth, producing a counterintuitive size-contamination relationship. Modeling indicated that walleye growth rate and diet were important explanatory variables when predicting Hg concentrations. Thus, hatchery contributions to freshwater systems in the form of energy and contaminants can influence diet, growth and Hg concentrations in sport fish. Given the extensive scale of fish stocking, and the known health risks associated with Hg contamination, this represents a significant issue for managers monitoring and manipulating freshwater food web structures, and policy makers attempting to develop fish consumption advisories to protect human health in stocked systems.

Ecotoxicology↗

USGS2008

Evaluating the effect of stressors on thiaminase activity in alewife

No consistent explanation has been found for the variability in the thiaminase activity of alewives Alosa pseudoharengus despite the role of alewife thiaminase in large-scale salmonine mortality in the Laurentian Great Lakes. We conducted experiments to evaluate the effect of two stressors, reduced salt content in the water and food limitation, on alewife thiaminase activity. Alewives were subjected to treatments in replicated tanks in which conductivity was lowered (<100 ??S/cm) for 8 d and feeding was limited for 39 d. Circulating white blood cells, plasma cortisol, plasma glucose, and whole-body thiaminase were measured in individual alewives to assess their response to these experimental treatments. Alewives from the controls had significantly larger numbers of circulating white blood cells than those in the salt-reduced and food-limited treatments (24,000 and 19,000 cells/??L and 11,000 and 9,000 cells/??L for alewives from the two control and salt-reduced treatment tanks, respectively, and 34,000 and 30,000 cells/??L and 21,000 and 16,000 cells/??L for alewives from the two control and food-limited treatment tanks). No significant differences in alewife thiaminase activity were found between treatment fish and their controls. The mean thiaminase activity in the alewives studied increased from 6,900 to 16,000 pmol??g -1??min-1 from the time of their collection in Cayuga Lake to the start of laboratory experiments 1.5-2.5 years later; the latter value was more than twice that of previously reported levels of thiaminase activity from alewives collected in the wild. These data suggest that the variability in alewife thiaminase is not related to stress from salt reduction or food limitation, but laboratory holding conditions significantly increased thiaminase through a mechanism not evaluated by our experimental treatments. ?? Copyright by the American Fisheries Society 2008.

Journal of Aquatic Animal Health↗