Physiological Measurements of Hg Stress in the Stream Minnow,

In fishes, many diagnostic measurements have been used to assess “stress” in response to environmental condition.  Stress indicators may include blood glucose and cortisol concentrations, white cell counts, metabolic rates, or changes in protein expression, to name a few.  Mercury (Hg), a well-known pollutant in aquatic systems, bioaccumulates in food webs and likely effects many physiological systems.  Limited physiological data exists on the effects of mercury exposure in stream fishes, particularly acute and chronic physiological effects associated with exposure.  We report here on the use of whole animal respirometry as a means of monitoring changes in metabolism in response to Hg stress.  Information on metabolism is indicative of energy partitioning and has previously been used to predict growth and potential fecundity of fishes.  Metabolic rates, as determined by oxygen consumption rates, were examined in the stream minnow, Campostoma oligolepis.  Fishes were collected from various Hg-free and Hg-contaminated streams.  Specifically, fish examined were collected from Shoal creek, a relatively pristine site in the Talladega National Forest, Mill creek, an urban site in Jacksonville, AL, and Snow creek, an urban, Hg-contaminated site in Oxford, AL.  Weight specific metabolic rates (MO₂) were significantly higher (~33%) for fishes inhabiting the Hg-contaminated site.  Previous studies have demonstrated gill damage and osmoregulatory stress in fishes chronically exposed to Hg.  We hypothesize that the observed increase in metabolism in fish from Hg contaminated sites in this study was associated with an increased energy demand associated with gill damage.