Mercury levels in two freshwater fishes from Panama's two largest lakes

Mercury contamination is a global concern, yet addressing it in developing nations is particularly challenging given the scarcity of data. In 2015, along with many other countries, Panama ratified the Minamata Convention on Mercury- a global effort to tackle mercury contamination and mitigate the risks it poses to humans and the environment. However, there are currently no published data from Panama on mercury contamination in freshwater fishes nor its associated health risks to humans from fish consumption. Here, we quantify for the first time the total mercury (THg) concentrations in two predatory fish species in Panama's two largest lakes: Lake Gatun and Lake Bayano. Within Lake Gatun, the native predator Hoplias microlepis ("pejeperro") had significantly higher predicted mercury concentrations (341.77 ng/g wet weight for a fish of 25 cm in standard length) than the introduced Cichla monoculus ("sargento" or "peacock bass") (196.98 ng/g), and mercury concentrations increased with fish size for both species. H. microlepis from Lake Gatun also had significantly higher predicted THg concentrations than H. microlepis from Lake Bayano (168.37 ng/g). Mercury concentrations at the aquatic food web baseline did not differ between lakes, as shown by the primary consumer snails Pomacea sp. Additionally, using stable isotopes of nitrogen (δ¹⁵N), we found that mercury concentrations increased with trophic position in both lakes (resulting in positive and significant Trophic Magnification Slopes), suggesting mercury biomagnification. Based on these findings, we provide fish consumption guidelines for both lakes, using the U.S. EPA current reference dose for mercury exposure. These results provide critical data for Panama as it works towards meeting the objectives set under the Minamata Convention.