Sublethal effects of methylmercury on the physiology of a small, coastal elasmobranch, smooth dogfish (Mustelus canis)
Date
2023
Authors
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Publisher
University of Delaware
Abstract
As mid to upper trophic level predators, elasmobranchs are well known to have elevated levels of mercury and its more toxic, organic form methylmercury (MeHg). The lethality of MeHg across different taxa has been well established, but its sublethal effects have only been investigated in depth at the scope of human health. The sub lethal effects of exposure to MeHg, which are known to impact animal physiology and behavior, remain largely undescribed in elasmobranchs. In this study, we established baseline information on how the physiology of a small, coastal elasmobranch (Mustelis canis, Smooth Dogfish) is impacted by chronic, sublethal exposure of this widespread and potent contaminant. We did this using a novel form of administering dietary MeHg to a relatively large fish in small research settings. We report our method could be used successfully to administer multiple levels of sublethal dosages of MeHg on a small elasmobranch. We assessed sublethal effects of different levels of exposure using different physiological parameters including aerobic scope estimates measured via oxygen consumption, growth rate, body condition, and food consumption. ☐ We found there were significant decreases in the specific growth rates for our high dose exposure group (piecewise regression, p<0.05) as well as food consumption (two-way ANOVA, p=0.0328), and healing. We also report trends of decreased absolute aerobic scope and increased standard metabolic rates for our low dose exposure, as well as inverse relationships for our high dose exposure. We saw no trends on maximum metabolic rates with regards to exposure level or time but do report there were significant decreases in exhaustion rates for our low and high dose treatment groups compared to our control (two-sample KS test , p=0.0096, p=0.038, respectively). Behaviors, such as foraging, prey capture, swimming, and behavior are critical for many species of elasmobranchs yet are likely impacted by exposure to MeHg. Hence, assessing effects on physiology and behavior after sub-lethal exposure can give us an idea of how important physiological processes may respond to exposure to this widespread and potent contaminant. ☐ In the future, we hope to investigate impacts on cognitive ability to due MeHg exposure, as well as compare metabolic rates and growth variables to the high concentrations of MeHg found in the heart, a rarely reported organ in mercury studies. We also hope to assess how this exposure impacted the overall energetic budget of the animals in order to assess how important physiological processes are reacting to contaminant.
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Keywords
Methylmercury, Coastal elasmobranch, Smooth dogfish, Oxygen consumption