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.     

137Cs elimination by chronically-contaminated largemouth bass (Micropterus salmoides)

The temperature-dependent 137Cs biological half-times (Tb) of lifetime-exposed largemouth bass (Micropterus salmoides) from a nuclear cooling reservoir at the U.S. Department of Energy's Savannah River Site were calculated from whole-body measurements of live fish and compared with literature records for acutely and chronically-contaminated fish. The Tb's of the bass averaged 322 d (95% CI: 311-333 d), 225 d (95% CI: 220 to 230 d), and 140 d (95% CI: 137 to 143 d) at 15, 20, and 26 degrees C, respectively. These mean Tb's were 1.7 to 2.5 times longer than would be expected for acutely contaminated fish, and 1.2 to 1.8 times longer than those predicted for fish at steady-state with their environment according to recent models. This slower elimination did not appear to result from slower elimination from skeletal muscle compared with other soft tissues, in that the muscle to whole-body 137Cs concentration ratios after the elimination period were similar to those of freshly-caught bass. Our results suggested that elimination rates estimated from the terminal elimination components of acutely-dosed fish may not reflect the elimination rates of fish exposed to contaminants throughout their lifetime, even when care is taken to allow sufficient time for absorption of the dose.     

Assessment of reproductive effects in largemouth bass (Micropterus salmoides) exposed to bleached/unbleached kraft mill effluents

This study evaluated the potential effects of different concentrations of bleached/unbleached kraft mill effluent (B/UKME) on several reproductive endpoints in adult largemouth bass (Micropterus salmoides). The kraft mill studied produces a 50/50 mix of bleached/unbleached market pulp with an estimated release of 36 million gal of effluent/day. Bleaching sequences were C₉₀d₁₀EopHDp and CEHD for softwood (pines) and hardwoods (mainly tupelo, gums, magnolia, and water oaks), respectively. Bass were exposed to different effluent concentrations (0 [controls, exposed to well water], 10, 20, 40, or 80%) for either 28 or 56 days. At the end of each exposure period, fish were euthanized, gonads collected for histological evaluation and determination of gonadosomatic index (GSI), and plasma was analyzed for 17β-estradiol, 11-ketotestosterone, and vitellogenin (VTG). Largemouth bass exposed to B/UKME responded with changes at the biochemical level (decline in sex steroids in both sexes and VTG in females) that were usually translated into tissue/organ-level responses (declines in GSI in both sexes and in ovarian development in females). Although most of these responses occurred after exposing fish to 40% B/UKME concentrations or greater, some were observed after exposures to 20% B/UKME. These threshold concentrations fall within the 60% average yearly concentration of effluent that exists in the stream near the point of discharge (Rice Creek), but are above the <10% effluent concentration present in the St. Johns River. The chemical(s) responsible for such changes as well as their mode(s) of action remain unknown at this time. Received: 3 January 2001/Accepted: 4 June 2001     

A comparison of the reproductive physiology of largemouth bass, Micropterus salmoides, collected from the Escambia and Blackwater Rivers in Florida

Largemouth bass (LMB), Micropterus salmoides, were taken from the Escambia River (contaminated site) and the Blackwater River (reference site) near Pensacola, Florida. The Escambia River collection occurred downstream of the effluent from two identified point sources of pollution. These point sources included a coal-fired electric power plant and a chemical company. Conversely, the Blackwater River's headwaters and most of its length flow within a state park. Although there is some development on the lower part of the Blackwater River, fish were collected in the more pristine upper regions. Fish were captured by electroshocking and were maintained in aerated coolers. Physical measurements were obtained, blood was taken, and liver and gonads were removed. LMB plasma was assayed for the concentration of 17ss-estradiol (E2) and testosterone using validated radioimmunoassays. The presence of vitellogenin was determined by gel electrophoresis (SDS-PAGE) and Western blotting using a monoclonal antibody validated for largemouth bass vitellogenin. No differences in plasma concentrations of E2 or testosterone were observed in females from the two sites. Similarly, males exhibited no difference in plasma E2. However, plasma testosterone was lower in the males from the contaminated site, as compared to the reference site. Vitellogenic males occurred only at the contaminated site. Additionally, liver mass was proportionately higher in males from the contaminated site, as compared to males from the reference site. These data suggest that reproductive steroid levels may have been altered by increased hepatic enzyme activity, and the presence of vitellogenic males indicates that an exogenous source of estrogen was present in the Escambia River.     

Effect of mercury on general and reproductive health of largemouth bass (Micropterus salmoides) from three lakes in New Jersey

The influence of mercury on the general and reproductive health of wild fish populations has not been well studied. Therefore, a variety of health and reproductive indicators were measured in male largemouth bass (Micropterus salmoides) collected from three bodies of water in New Jersey: Assunpink Lake, Manasquan Reservoir, and Atlantic City Reservoir. The mean mercury content in fish muscle from Assunpink Lake was 0.30 microg/g; from Manasquan Reservoir, 1.23 microg/g; and from Atlantic City Reservoir, 5.42 microg/g. Body weight, length, condition factor, and gonadosomatic index were similar for all three lakes. Furthermore, there was no significant relationship between muscle mercury content and adrenocortical function, indicated by interrenal nuclear diameter and serum cortisol levels following stress. Bass from the Atlantic City Reservoir had a slightly lower, although significant, liver somatic index than bass from the two other lakes. A significant, positive correlation between 11-ketotestosterone serum concentrations and mercury muscle content was detected, although no significant relationship between testosterone serum concentrations and mercury muscle content was found. The findings of this study suggest that, while elevated levels of mercury in fish potentially alter androgen profiles, they do not substantially decrease other indicators of general and reproductive health.     

Silver toxicity and accumulation in largemouth bass and bluegill

Summary Exposure of juvenile largemouth bass and bluegill to silver (0.3 to 70 ug/liter) resulted in accumulation of this metal. The quantity of metal accumulated increased as exposure concentration increased with a subsequent equilibrium developing between the water and tissue concentrations. Metal accumulations in the bass tissues were highest in the internal organs, followed by the gills and remainder of the body. The greatest increase was exhibited in the gills. Zinc concentrations in the bass body remainder and the bluegill total body appeared to vary in an approximately inverse relationship to the initial accumulation of silver within the tissues. The bass were more sensitive to silver than the bluegill. Abnormal behavior patterns were observed in both species.     

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     

Factors Controlling Mercury and Methylmercury Concentrations in Largemouth Bass (Micropterus salmoides) and Other Fish from Maryland Reservoirs

The concentration of mercury (Hg) and methylmercury (MeHg) was determined for largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus) and black crappie (Pomoxis nigromaculatus) from Maryland reservoirs. Overall, there was a large difference in normalized bass MeHg concentration (for fish of ∼370 mm) between the reservoirs, ranging from <100 ng g⁻¹ to almost 800 ng g⁻¹. Furthermore, the relationship between fish weight and MeHg concentration varied substantially between lakes, and showed no geographical relationship. The concentration of Hg, MeHg and ancillary parameters were determined in the water and correlations were sought between the normalized concentration of MeHg in bass and both physical and chemical parameters of the reservoirs, as well as the concentration of MeHg in the prey of the largemouth bass. Bass MeHg concentration correlated with dissolved MeHg and dissolved organic carbon, but not with other chemical parameters. There was no relationship to physical characteristics that varied over orders of magnitude for these reservoirs. Dissolved MeHg did not correlate with any chemical or physical attributes. Overall, this study suggests that water column MeHg is a good predictor of fish concentration but that the water column MeHg cannot be predicted based on usually measured chemical and physical characteristics of fresh water bodies.     

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.     

Reproductive and biochemical biomarkers in largemouth bass sampled downstream of a pulp and paper mill in Florida

The objective of this study was to evaluate the effects of bleached/unbleached kraft mill effluents (B/UKME) on the reproductive parameters of free-ranging Florida largemouth bass (Micropterus salmoides floridanus). The reproductive parameters measured included gonadosomatic index (GSI), histological evaluation of gonads, and plasma concentrations of vitellogenin (VTG), 17beta-estradiol, and 11-ketotestosterone (11-KT). Hepatic ethoxyresorufin-O-deethylase (EROD) activity was measured as a marker of exposure to cytochrome P450-inducing agents in these effluents. Endpoints were compared among adult bass sampled from tributary and mainstream effluent-contaminated and reference sites. Females sampled from the site closest to the mill outfall had a significant five-fold increase in EROD activity compared to bass sampled from reference streams. Although sex hormones were significantly reduced in bass from exposed sites, there were no differences in VTG and GSI across sites. The absence of organism-level responses was probably not related to a lack of sensitivity, as previous studies in our laboratory have shown that bass exposed to these effluents exhibit changes in GSI and in other measures associated with reproductive success. In females, inverse relationships were observed between VTG and GSI and EROD activity. These relationship, however, were not consistent within all of the sites studied. Collectively, our findings indicate that hepatic EROD induction is an effective marker of B/UKME exposure in largemouth bass and that it might be associated with antiestrogenic effects in this species.     

Survival of vaccinated,feed-trained largemouth bass fry (Micropterus salmoides floridanus) during natural exposure to Flavobacterium columnare

Vaccinated, feed-trained largemouth bass fry (Micropterus salmoides floridanus) were cohabited with sham-vaccinated fish. Fish were exposed, under natural conditions, to Flavobacterium columnare, a ubiquitous bacterium associated with columnaris disease. During every time interval, the probability that a vaccinated fish would survive past time, t, was greater than for sham-vaccinated fish and survivor functions were significantly different (p-value <0.001). Overall, vaccinated fish had a 43% lower risk of death during the field trial. Overall incidence was 1.7 times greater for the sham-vaccinated (1.4%/d) as compared to the vaccinated fish (0.8%/d). Vaccination with AQUAVAC-COL (Intervet/Schering-Plough Animal Health) significantly reduced the risk of death from columnaris disease in feed-trained largemouth bass fry.     

Mercury in livers of wading birds (ciconiiformes) in southern Florida

Mercury was measured in livers from 144 wading birds representing seven species collected from four different areas in southern Flordia, including the Everglades National Park. Significant differences in hepatic mercury concentrations were identified between birds collected from different geographic locations, birds of different ages, dietary factors, and relative amounts of body fat. Birds collected from an area encompassing the central Everglades and eastern Florida Bay had significantly greater concentrations of hepatic mercury than did birds from other collection areas. Livers from fledgling and young adult birds contained approximately three times the concentration of mercury as livers from nestling birds. Bird species whose prey base consists of larger fish were found to have approximately four times the hepatic concentration of mercury as did those species which consume smaller fish or crustaceans. Birds with minimal to moderate amounts of body fat had two to three times the concentration of hepatic mercury as birds with relatively abundant body fat reserves. Four great blue herons collected from the central Everglades contained liver mercury at concentrations typically associated with overt neurologic signs (30 g/g). Between 30% and 80% of potential breeding-age birds collected from this area contained hepatic mercury at concentrations associated with reproductive impairment in ducks and pheasants. These data suggest that declining numbers of nesting ciconiiform birds in Florida may be due, in part, to mecury contamination of their food supply.     

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.     

Manufactured nanomaterials (fullerenes, C60) induce oxidative stress in the brain of juvenile largemouth bass

Although nanotechnology has vast potential in uses such as fuel cells, microreactors, drug delivery devices, and personal care products, it is prudent to determine possible toxicity of nanotechnology-derived products before widespread use. It is likely that nanomaterials can affect wildlife if they are accidentally released into the environment. The fullerenes are one type of manufactured nanoparticle that is being produced by tons each year, and initially uncoated fullerenes can be modified with biocompatible coatings. Fullerenes are lipophilic and localize into lipid-rich regions such as cell membranes in vitro, and they are redox active. Other nano-sized particles and soluble metals have been shown to selectively translocate into the brain via the olfactory bulb in mammals and fish. Fullerenes (C60) can form aqueous suspended colloids (nC60); the question arises of whether a redox-active, lipophilic molecule could cause oxidative damage in an aquatic species. The goal of this study was to investigate oxyradical-induced lipid and protein damage, as well as impacts on total glutathione (GSH) levels, in largemouth bass exposed to nC60. Significant lipid peroxidation was found in brains of largemouth bass after 48 hr of exposure to 0.5 ppm uncoated nC60. GSH was also marginally depleted in gills of fish, and nC60 increased water clarity, possibly due to bactericidal activity. This is the first study showing that uncoated fullerenes can cause oxidative damage and depletion of GSH in vivo in an aquatic species. Further research needs to be done to evaluate the potential toxicity of manufactured nanomaterials, especially with respect to translocation into the brain.