Virginia Scientists Examine Contaminant Levels in Bay Blue Cats
As Blue Catfish is an invasive species in the tributaries of the Chesapeake Bay, the first method people think of to control the species is human consumption. “If you can’t beat them, eat them” is a common phrase you hear in the promotion of what is often called “invasivorism”. The mild taste and firm flesh of catfish make them popular among seafood consumers. Consequently, catfish are the most commonly raised fish in aquaculture in the United States (USDA 2014). Although there is interest in expanding commercial markets for wild-caught Chesapeake Blue Catfish, contaminants present a concern for growth of commercial fisheries. Catfish inspections are conducted under the US Department of Agriculture (USDA) without screening for contaminants like other seafood regulated under the US Food and Drug Administration (FDA).
Chesapeake Bay Blue Catfish Tacos. Photo by Donald J. Orth.
Contaminants are substances present in the environment at concentrations greater than they would be naturally. Fish assimilate environmental contaminants into their tissues, where they accumulate over time in a process called bioaccumulation. When a fish is eaten by a predator, the prey’s contaminant load is then assimilated into the predator’s tissues. This continues up the food chain with higher level predators potentially carrying higher contaminant loads, a process called biomagnification. As many contaminants present human health risks, it is important to understand their prevalence in the environment and our food. The US Environmental Protection Agency (EPA) and state health officials provide recommendations for consumption of many contaminants in fish based on the number of half-pound (8 oz) meals over a month. Generally, pregnant women, women of child-bearing age and children are especially encouraged to limit their exposure to contaminants by reducing fish consumption.
Scientists from Virginia Institute of Marine Science and College of William & Mary recently published a paper examining the contaminant loads in Blue Catfish from three tributaries of the Chesapeake Bay. They collected fillet samples from Blue Catfish from the James, Rappahannock and Potomac rivers to analyze the concentrations of nine contaminants.
Sampling sites for Blue Catfish assessed for contaminants loads, where black dots indicate upper sampling sites and red dots indicate lower sampling sites within river systems. Figure 1: Luellen et al. 2018. Environmental Science and Pollution Research 25:28355–28366.
Contaminants examined by Luellen et al. (2018) in Chesapeake Bay tributary Blue Catfish. * indicates a compound that is not manufactured, but a contaminant created by degradation or production of a manufactured product. EPA Limits indicate whether or not the US Environmental Protection Agency has consumption recommendations in place for the contaminant.
Contaminant levels differed by Blue Catfish size and river system in the three rivers examined. Larger Blue Catfish generally had higher concentrations of mercury, PCBs, DDT, chlordanes and PBDEs in at least two river systems for each of the contaminants examined. In this study, the sizes examined did not encompass the full range of Blue Catfish sizes in these rivers, thus findings are applicable within the ranges; James: 13–42 in., Rappahannock: 12– 26 in., Potomac: 12–23 in. from the tip of the snout to the fork of the tail. Fish from the upper James and upper Potomac had the highest contaminant loads for many of the contaminants examined, with lower loads for the lower James and Rappahannock rivers. Contaminant loads in individual fish were variable. However, many fish had loads for one or more contaminants that exceeded EPA guidelines for unrestricted consumption (> 16 meals/month). Although the EPA standards provide recommendations for consumption of individual contaminants, we don’t know if or how these contaminants interact with each other and if standards should be adjusted accordingly.
Mercury levels (Hg) in individual Chesapeake Bay tributary Blue Catfish by river system in relation to EPA limits for human consumption. Labels on dashed lines indicate the threshold of the associated consumption advisory level. Supplementary Figure 1 from Luellen et al. 2018. Environmental Science and Pollution Research 25:28355–28366.
What can you do to limit your exposure?
Eat smaller fish – In several cases, contaminant levels were higher in larger fish than small fish. Larger fish are generally older and have had a longer time period in which to accumulate toxins and may feed at higher trophic levels.
Be selective about where you eat fish from – In this study, the authors report the upper James and Potomac rivers had the highest contaminant loads in many cases. While there was no comparison with the lower Potomac, the lower James did typically have lower contaminant loads than the upper James. The Rappahannock typically had the lowest contaminant loads and may be the safest alternative of the four localities examined here.
Follow consumption advisories – Both Virginia and Maryland have consumption advisories available to limit your exposure to contaminants. Be sure to consult those advisories before you go fishing and know what sizes of fish may be safest to keep.
See the original article for more details.
Luellen, D.R., M.J. LaGuardia, T.D. Tuckey, M.C. Fabrizio, G.W. Rice and R.C. Hale. 2018. Assessment of legacy and emerging contaminants in an introduced catfish and implications for the fishery. Environmental Science and Pollution Research 25:28355–28366.
United States Department of Agriculture. 2014. Census of Agriculture: Census of Aquaculture 2013. Volume 3, special studies, part 2. https://www.agcensus.usda.gov/Publications/2012/Online_Resources/Aquaculture/Aqua.pdf