Mercury Concentrations in Largemouth Bass (Micropterus salmoides) Collected from Ash Meadows National Wildlife Refuge, Nye County, Nevada

Mercury is a known neurotoxin and contaminant of concern worldwide. Mercury may occur at elevated concentrations adjacent to industrial sources, such as coal-fired power plants, or in remote environments and newly filled water bodies. Mercury tissue concentrations were determined for a sample of largemouth bass (Micropterus salmoides) from Crystal Reservoir, Ash Meadows National Wildlife Refuge, Nye County, Nevada. This investigation was triggered by (1) the presence of several conditions in soil and water that facilitate mercury bioaccumulation, (2) previous investigations that detected mercury in source springs, and (3) the presence of game fish and endangered pupfish within the reservoir. Mercury concentrations were significantly correlated with both fish mass and condition, but were lower than national human health and safety standards. It is possible that high pH and salinity inhibited methylation and subsequent bioaccumulation; however, additional studies are needed to determine causation of the low concentration in fish tissue compared with ambient conditions.     

Seasonal Changes and Tissue Distribution of Mercury in Largemouth Bass (Micropterus salmoides) from Dorena Reservoir, Oregon

Mercury contamination in fish has lead to the issuance of fish consumption advisories in many water bodies of the United States. There is evidence that mercury concentrations may fluctuate seasonally, which could affect consumption advisories. Largemouth bass (Micropterus salmoides) were collected from Dorena Reservoir, Oregon, in spring and summer of 1995 and spring, summer, and fall of 1996. Samples of muscle, liver, and gonad were analyzed for total mercury. There were seasonal differences for mercury in liver and gonads, but not muscle tissue. Liver mercury concentrations were higher in summer and lower in spring whereas ovarian mercury concentrations were higher in fall and lower in spring. This study shows that liver tissue was more sensitive than muscle tissue to seasonal variability of mercury, but these seasonal fluctuations may not influence consumption advisories. Received: 20 April 1999/Accepted: 27 July 1999     

Mercury in Fish Scales as an Assessment Method for Predicting Muscle Tissue Mercury Concentrations in Largemouth Bass

The relationship between total mercury (Hg) concentration in fish scales and in tissues of largemouth bass (Micropterus salmoides) from 20 freshwater sites was developed and evaluated to determine whether scale analysis would allow a nonlethal and convenient method for predicting Hg concentrations in tissues. The relationship between total Hg concentration in untreated scale samples and muscle tissue is highly variable. Several different scale treatments were tried in an effort to increase the coefficient of determination and thereby enhance the effectiveness of this predictive technique. Washing scales with acetone, deionized (DI) water, detergent solution, and soap were used in conjunction with ultrasonication. The use of a mild soap solution with heating and ultrasonication increased the r² the most (from 0.69 [untreated scales] to 0.89). However, despite treatment, wide predictions of tissue Hg concentration remained. These results suggest that application of this technique as an independent method for issuance of fish advisories is inappropriate. Nevertheless, our results showed that scale analysis has potential for assessing general trends in concentration relative to a tissue criterion and for assessing Hg contamination in fish tissue as a first-level screen.     

Assessing Mercury Exposure and Biomarkers in Largemouth Bass (Micropterus Salmoides) from a Contaminated River System in California

We evaluated mercury (Hg) exposure and two biomarkers, metallothionein (MT) gene expression and histopathological alterations in a wild fish species, largemouth bass (Micropterus salmoides), collected from the Sacramento-San Joaquin Delta, CA, a region polluted with Hg from historic mining activities. Hg is highly toxic and can disrupt multiple physiological systems in vertebrate species, including the immune system. Total mercury (THg) concentration in muscle tissue ranged from 0.12 to 0.98 ppm (wet weight) and was not related to body condition (r ² = 0.005, p = 0.555). Using linear regression analysis, we found a positive relationship between MT gene expression (as determined using quantitative polymerase chain reaction) and copper, zinc, manganese, aluminum, and nickel (decreased to one variable by way of principal component analysis) (r ² = 0.379, p = 0.044), a negative relationship with selenium (r ² = 0.487, p = 0.017), and a weak, negative relationship with THg concentrations (r ² = 0.337, p = 0.061). Juvenile largemouth bass collected from Hg-contaminated areas displayed histopathological features of immunosuppression compared with those collected from less contaminated areas as evidenced by significantly lower macrophage density in kidney and liver tissue (p = 0.018 and 0.020, respectively), greater trematode density in liver tissue (p = 0.014), and a greater number of adult trematodes. Our results suggest that largemouth bass may be experiencing sublethal effects from chronic Hg exposure. Furthermore, our findings illustrate the utility of examining multiple sublethal markers of effect to assess the impacts of contaminant exposure on physiological function in wild species.     

Liver Cell Estrogen Receptor Binding in Prespawning Female Largemouth Bass, Micropterus salmoides, Environmentally Exposed to Polychlorinated Biphenyls

Estrogen-receptor–like binding was partially characterized in liver tissue of prespawning female largemouth bass, Micropterus salmoides (LMB). Saturation and Scatchard analyses exhibited estrogen binding activity with high affinity (K_d in the 10⁻⁹ M range) and limited capacity (nuclear = 37.4 fmol/g tissue; cytosol = 234 fmol/g tissue). Androgens, progestins, and cortisol competed poorly for binding in competition studies. Thus, LMB liver estrogen binding activity possesses similar properties to estrogen receptors (ER) described in other vertebrates. In a study of prespawning female LMB from Lake Hartwell, SC/GA, a reservoir contaminated by polychlorinated biphenyls (PCBs), individuals environmentally exposed to high levels of PCBs had significantly lower ER binding capacity (Bmax) and higher nonspecific binding (NS) than fish from a relatively uncontaminated reference location. Fish obtained at a site with intermediate levels of PCBs did not exhibit the expected decrease in Bmax. The lower Bmax observed in fish from the location with high PCB contamination is consistent with the reported behavior of liver ER in fish experimentally exposed to PCBs. Increased NS in the ER assays could be related to elevations in albumin associated with the PCB exposure. Received: 15 July 1996/Revised: 17 September 1996     

Mercury accumulation in largemouth bass (Micropterus salmoides) in a Florida Lake

Rates of mercury accumulation were examined in male and female largemouth bass (Micropterus salmoides) from Lake Tohopekaliga, Florida, to establish methods for fish consumption advisories for the protection of human health. In addition, concentrations were determined in five lower trophic level fish species. Total mercury concentrations in adult largemouth bass muscle tissue ranged from 0.16 to 1.10 g/g (fresh weight) and increased as fish increased in size and age. Wholebody mercury concentrations of 1990 year-class largemouth bass increased from 0.05 g/g at 20 mm and to 0.32 g/g at 320 mm (age 2). Significant differences were found in the rates of accumulation between sexes for length and weight, but not for age. Therefore, standardized mercury concentrations were determined using bass age to make comparisons among sampling dates. Although there were significant differences in adjusted mean mercury concentrations among two sampling dates, mercury content of standard-age bass remained relatively constant over time. Largemouth bass exceed the Florida Health Advisory level for limited consumption of fish (0.50 g Hg/g) based on a mean concentration of 0.59 g/g for 64 bass. Advisories based on fish morphological characteristics (i.e., length, weight) or age are not possible for Lake Tohopekaliga due to differences in mercury accumulation in male and female bass. Lower trophic level species of sport fish did not exceed the limited consumption level.     

Total Mercury Concentrations in Lakes and Fish of Western Maryland, USA

The purpose of this study was to quantify total mercury concentrations in three species of fish in three lakes of western Maryland: Piney Creek reservoir, Deep Creek Lake, and Lake Habeeb. We measured total mercury concentrations in water from each lake and muscle tissue from 119 fish collected in fall 2000: 15 largemouth bass (Micropterus salmoides), 15 yellow perch (Perca flavescens), and 15 bluegill (Lepomis macrochirus) from the Piney Creek reservoir; 15 largemouth bass, 15 yellow perch, and 14 bluegill from Deep Creek Lake; and 15 largemouth bass and 15 bluegill from Lake Habeeb. Average total mercury concentrations (± SD) in surface waters were 0.96 ± 0.03 ng L⁻¹ for the Piney Creek reservoir, 0.56 ± 0.07 ng L⁻¹ for Deep Creek Lake, and 0.40 ± 0.05 ng L⁻¹ for Lake Habeeb. These water quality differences were sometimes reflected in the total mercury concentration in fish muscle tissue. Total mercury concentrations in bluegill (0.05 ± 0.02 μg g⁻¹) and largemouth bass (0.10 ± 0.03 μg g⁻¹) from Lake Habeeb were significantly (p < 0.001) lower than the total mercury concentrations in bluegill and largemouth bass from the Piney Creek reservoir (bluegill: 0.13 ± 0.04 μg g⁻¹ and largemouth bass: 0.37 ± 0.18 μg g⁻¹) and Deep Creek Lake (bluegill: 0.11 ± 0.04 μg g⁻¹ and largemouth bass: 0.30 ± 0.09 μg g⁻¹). Yellow perch from the Piney Creek reservoir had significantly higher total mercury concentrations than yellow perch from Deep Creek Lake (0.20 ± 0.08 μg g⁻¹ versus 0.13 ± 0.04 μg g⁻¹). In contrast, total mercury concentrations in largemouth bass from the Piney Creek reservoir and Deep Creek Lake were not significantly different. With the exception of largemouth bass from Lake Habeeb and yellow perch from Deep Creek Lake, there were relatively strong (r ² > 0.39–0.79) log-log relationships between the size (weight and length) of the fish and total mercury concentrations in muscle tissue. The largest largemouth bass (> 800 g and > 38 cm) from both Deep Creek Lake and the Piney Creek reservoir had total mercury concentrations that exceeded the consumption advisory of 0.5 μg g⁻¹ that is used by many states and Canada. In contrast, total mercury concentrations in largemouth bass from Lake Habeeb did not exceed this consumption advisory. Our results suggest that fish consumption advisories are needed for largemouth bass in the Piney Creek reservoir and Deep Creek Lake. Received: 8 August 2001/Accepted: 1 December 2001     

Mercury accumulation by largemouth bass (Micropterus salmoides) in recently impounded reservoirs

Summary Mercury levels of largemouth bass from three reservoirs in the southeastern United States were highest in the younger, relatively oligotrophic reservoirs and were significantly lower in an older, more eutrophic reservoir in the same drainage system. The reservoir with the highest mercury levels in bass is the reservoir farthest upstream, and is not subject to inputs of municipal or industrial wastes. The source of mercury in these reservoirs appears to be the soil which formed their original sediments. Preliminary data indicate that mercury levels in largemouth bass in these systems decline as the reservoirs age. Elevated mercury levels in fish appear to be a transitory phenomenon in newly impounded, relatively oligotrophic reservoirs.     

A Survey of Size-Specific Mercury Concentrations in Game Fish from Maryland Fresh and Estuarine Waters

A survey of size-specific mercury (Hg) concentrations in game fish from a subset of Maryland fresh and estuarine waters was conducted, in which Hg concentrations in 112 fish from seven freshwater impoundments and three tidal and four estuarine locations in Chesapeake Bay and its tributaries were measured. Striped bass (Morone saxatilis) was the most intensively examined species. Of the fish examined, the largest freshwater sportfish contained the highest Hg concentrations. Striped bass and largemouth bass (Micropterus salmoides) from Chesapeake Bay and its tributaries contained less Hg at the same size than the same species in fresh waters. Large striped bass, chain pickerel (Esox niger), and walleye (Stizostedion vitreum) from Deep Creek Lake and Liberty Reservoir exceeded the FDA action level of 1 mg Hg/kg. Striped bass, largemouth bass, and white crappie (Pomoxis annularis) in other impoundments equaled or exceeded a common advisory level of 0.5 mg Hg/kg. Large differences in size-normalized Hg concentrations among lakes and particularly between fresh and salt waters highlight the large differences in MeHg production and bioaccumulation among ecosystems. This work indicates that a more comprehensive study of Hg in Maryland fish is warranted to protect human and wildlife health. Received: 16 November 1999/Accepted: 28 December 1999     

Methylmercury Concentrations in Six Fish Species from Two Colombian Rivers

The objective of this study was to determine whether fish collected from the La Miel or Nechí Rivers (Colombia) differed in muscle methyl mercury (meHg) concentration. Two fish from six different species were collected from markets adjacent to each river. Overall, fish collected from the market adjacent to the Nechí River contained higher levels of meHg. This result however is being driven by very high meHg concentrations in four individual fish, three of which are Pimelodid, long-whiskered catfish. These catfish may represent ideal sentinel organism for the detection of meHg contamination in Colombian rivers.     

Mercury Concentrations in Commercial Fish from Freshwater and Saltwater

Research was performed to investigate the concentration of mercury in muscle and liver of fish species from freshwater (Barbus xanthopterus, Barbus grypus, Liza abu) and saltwater (Cynoglossus arel, Periophthalmus waltoni, Otolithes ruber) in Khouzestan, Iran. In freshwater fish, muscle was polluted in comparison with liver except for Barbus xanthopterus which high levels of mercury were measured in liver. In saltwater fish liver was contaminated than muscle except for Cynoglossus arel which high level of mercury was found in muscle. Significant variations in metal values were evaluated using student’s t test at P < 0.05. Mercury concentrations were well above the permissible limits suggested by WHO and FDA guidelines.     

Factors Controlling the Bioaccumulation of Mercury, Methylmercury, Arsenic, Selenium, and Cadmium by Freshwater Invertebrates and Fish

Concentrations of mercury (Hg), methylmercury (MMHg), arsenic (As), selenium (Se), and cadmium (Cd) were measured in atmospheric deposition, stream water, and biota in two streams in western Maryland. Overall, concentrations were slightly higher in the water of the lower pH Herrington Creek tributary (HRCT). Bioaccumulation factors were also higher for HRCT compared to Blacklick Run (BLK). MMHg concentrations in biota increased with trophic level and essentially all the Hg was as MMHg in predatory insects and insectivorous/carnivorous fish. Thus, the overall trophic status of the organism was indicated by the %MMHg in its tissues. Levels of As, Se, Cd, and Hg, however, decreased with increasing trophic level. Adsorption of As to the exoskeleton of invertebrates appears to be an important accumulation mechanism. MMHg was distributed evenly throughout crayfish and fish organs, whereas As, Se, Cd, and Hg were found in higher concentrations in detoxifying organs. Concentrations in biota in this study were somewhat elevated compared to other rural sites, but were less than those of point source–contaminated sites. Overall, as atmospheric inputs to the two watersheds were similar, the results of this study show the importance of water chemistry in determining the bioaccumulation of the metals and metalloids into insects. Subsequent transfer to higher trophic levels is related to both the ability of the organisms to depurate and the mode of accumulation, either directly from water or from food. Received: 19 April 1999/Accepted: 12 October 1999     

Methylmercury Concentrations in Fish from Tidal Waters of The Chesapeake Bay

Striped bass (Morone saxatilis), white perch (Morone Americana), and largemouth bass (Micropterus salmoides) were collected in the Chesapeake Bay mainstem and tributaries and analyzed for total mercury (Hg) and methylmercury (MeHg) content. Striped bass are anadromous, whereas white perch and largemouth bass are resident species, and the largemouth bass are also restricted to the tidal fresh portion of the Bay. Total Hg and MeHg concentrations in striped bass increased with fish size, and large fish (>7.5 kg wet weight) tended to have MeHg concentrations of 300 ng g⁻¹ or greater. On average, the striped bass MeHg concentration was 120 ± 100 ng g⁻¹ and the fraction of the total Hg as MeHg was 65 ± 22%. Reasons for the lower relative MeHg content are discussed. Otolith strontium/calcium ratios were also determined to examine whether migration had a significant impact on MeHg content in striped bass. Resident fish did appear to have a higher MeHg burden than the more migratory fish of similar size. Largemouth bass and white perch tended to have low MeHg content (respectively, 14 ± 7 and 13 ± 11 ng g⁻¹; all fish <1 kg wet weight), and the white perch also had a low %MeHg (28 ± 14%), reflecting their mostly planktivorous lifestyle. A comparison of largemouth bass and striped bass MeHg concentrations for the estuarine fish with those of fish in Maryland reservoirs of similar size showed that the estuarine fish have much lower MeHg burdens. Differences in MeHg concentration in the estuarine waters compared to the reservoir waters likely account for much of this difference, although the importance of other factors is also discussed.     

Mercury Concentrations in the Fish Community from Indrawati River,Nepal

This study quantified concentrations of mercury (Hg) and its trophic transfer along the fish community in the Indrawati River, Nepal. Stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C), complemented by stomach contents data were used to assess the food web structure and trophic transfer of Hg in 54 fishes; 43 Shizothorax richardsonii and 11 Barilius spp. [B. bendelisis (1), B. vagra (3) and B. barila (7)]. Sixty-one muscle samples (including six replicates) were used for the analysis of total mercury (THg) and stable isotopes. Mean THg concentrations in B. spp. and the more common species S. richardsonii was observed to be 218.23 (ng/g, ww) and 90.82 (ng/g, ww), respectively. THg versus total length in both S. richardsonii and B. spp. showed a decreasing tendency with an increase in age. Regression of logTHg versus δ¹⁵N among the fish species showed a significant positive correlation only in S. richardsonii indicating biomagnification along the trophic level in this species.     

Postimpoundment Time Course of Increased Mercury Concentrations in Fish in Hydroelectric Reservoirs of Northern Manitoba, Canada

Mercury (Hg) concentrations in fish in boreal reservoirs have been shown to be increased for up to 3 decades after impoundment. However, the time course of increased concentrations is not well known. The purpose of this study was to determine the evolution of Hg concentrations in fish in the boreal reservoirs of northern Manitoba, Canada, and its relationship with severity of flooding. We determined total Hg concentrations in three species of fish for up to 35 years after impoundment in 14 lakes and lake basins. Postimpoundment trends depended on fish species and reservoir. In the benthivorous lake whitefish (Coregonus clupeaformis), Hg concentrations increased after flooding to between 0.2 and 0.4 μg g⁻¹ wet weight compared with preimpoundment concentrations between 0.06 and 0.14 μg g⁻¹ and concentrations in natural lakes between 0.03 and 0.06 μg g⁻¹. Hg concentrations in lake whitefish were usually highest within 6 years after lake impoundment and took 10 to 20 years after impoundment to decrease to background concentrations in most reservoirs. Hg concentrations in predatory northern pike (Esox lucius) and walleye (Sander vitreus) were highest 2 to 8 years after flooding at 0.7 to 2.6 μg g⁻¹ compared with preimpoundment concentrations of 0.19 to 0.47 μg g⁻¹ and concentrations in natural lakes of 0.35 to 0.47 μg g⁻¹. Hg concentrations in these predatory species decreased consistently in subsequent years and required 10 to 23 years to return to background levels. Thus, results demonstrate the effect of trophic level on Hg concentrations (biomagnification). Peak Hg concentrations depended on the amount of flooding (relative increase in lake surface area). Asymptotic concentrations of approximately 0.25 μg g⁻¹ for lake whitefish and 1.6 μg g⁻¹ for both walleye and northern pike were reached at approximately 100% flooding. Downstream effects were apparent because many reservoirs downstream of other impoundments had higher Hg concentrations in fish than would be expected on the basis of flooding amount.     

Evaluation of Potentially Nonlethal Sampling Methods for Monitoring Mercury Concentrations in Smallmouth Bass (<Emphasis Type="Italic">Micropterus dolomieu</Emphasis>)

We evaluated three potentially nonlethal alternatives to fillet sampling for the determination of mercury (Hg) concentrations in smallmouth bass (Micropterus dolomieu). Fish (n = 62, 226–464 mm total length) from six sites in southern Missouri were captured by electrofishing. Blood samples (1 mL) from each fish were obtained by caudal veinipuncture with a heparinized needle and syringe. Biopsy needle (10 mm × 14 gauge; three cuts per fish; 10–20 mg total dry weight) and biopsy punch (7 mm × 5 mm in diameter, one plug per fish, 30–50 mg dry weight) samples were obtained from the area beneath the dorsal fin. Fillet samples were obtained from the opposite side of the fish. All samples were freeze-dried and analyzed for total Hg by combustion amalgamation atomic absorption spectrophotometry. Mean relative standard deviations (RSDs) of triplicate samples were similar for all four methods (2.2–2.4%), but the range of RSDs was greater for blood (0.4–5.5%) than for the muscle methods (1.8–4.0%). Total Hg concentrations in muscle were 0.0200–0.8809 μg/g wet weight; concentrations in plug, needle, and fillet samples from each fish were nearly identical. Blood Hg concentrations were 0.0006–0.0812 μg/mL and were highly correlated with muscle concentrations; linear regressions between log-transformed blood and fillet Hg concentrations were linear and statistically significant (p < 0.01), and explained 91–93% of the total variation. Correlations between fillet Hg concentrations and fish size and age were weak; together they explained ≤37% of the total variation, and the relations differed among sites. Overall, any of the alternative methods could provide satisfactory estimates of fillet Hg in smallmouth bass; however, both blood and plug sampling with disposable instruments were easier to perform than needle sampling. The biopsy needle was the most difficult to use, especially on smaller fish, and its relative expense necessitates reuse and, consequently, thorough cleaning between fish to prevent cross-contamination.