Bioaccumulation of Trace Mercury in Trophic Levels of Benthic, Benthopelagic, Pelagic Fish Species, and Sea Birds from Arvand River, Iran

In this study, concentration of mercury was determined in the trophic levels of benthic, benthopelagic, pelagic fish species, and river birds from Arvand River, located in the Khuzestan province in the lowlands of southwestern Iran at the head of the Persian Gulf. The order of mercury concentrations in tissues of the fish species was as follows: liver>gill>muscle and in tissues of the kingfisher species was as follows: feather>liver>kidney>muscle. Therefore, liver in fish and feather in kingfisher exhibited higher mercury concentration than the other tissues. There was a positive correlation between mercury concentrations in fish and kingfisher species with size of its food items. We expected to see higher mercury levels in tissues of female species because they are larger and can eat larger food items. The results of this study show that the highest mean mercury level were found in the kingfisher (Anas crecca), followed by benthic (Epinephelus diacanthus), benthopelagic (Chanos chanos), and pelagic fish (Strongylura strongylura). Mean value of mercury in fish species, S. strongylura were (0.61 μg g^?1 dry weight), C. chanos (0.45 μg g^?1 dry weight), E. diacanthus (0.87 μg g^?1 dry weight), and in kingfisher species A. crecca was (2.64 μg g^?1 dry weight). Significant correlation between mercury concentration in fish and kingfisher may be related to high variability of mercury in the fish.     

The functional importance of <Emphasis Type="Italic">Acropora austera</Emphasis> as nursery areas for juvenile reef fish on South African coral reefs

Many coral reef fish species use mangrove and seagrass beds as nursery areas. However, in certain regions, the absence or scarcity of such habitats suggests that juvenile coral reef fish may be seeking refuge elsewhere. The underlying biogenic substratum of most coral reefs is structurally complex and provides many types of refuge. However, on young or subtropical coral reefs, species may be more reliant on the living coral layer as nursery areas. Such is the case on the high-latitude coral reefs of South Africa where the coral communities consist of a thin veneer of coral overlaying late Pleistocene bedrock. Thus, the morphology of coral species may be a major determinant in the availability of refuge space. Acropora austera is a branching species that forms large patches with high structural complexity. Associated with these patches is a diverse community of fish species, particularly juveniles. Over the past decade, several large (>100 m²) A. austera patches at Sodwana Bay have been diminishing for unknown reasons and there is little evidence of their replacement or regrowth. Seven patches of A. austera (AP) and non-A. austera (NAP) were selected and monitored for 12 months using visual surveys to investigate the importance of AP as refugia and nursery areas. There were significant differences in fish communities between AP and NAP habitats. In total, 110 species were recorded within the patches compared to 101 species outside the patches. Labrids and pomacentrids were the dominant species in the AP habitats, while juvenile scarids, acanthurids, chaetodons and serranids were also abundant. The diversity and abundance of fish species increased significantly with AP size. As the most structurally complex coral species on the reefs, the loss of APs may have significant implications for the recruitment and survival of certain fish species.     

Genetic effects of living in a highly polluted environment: the case of the silverside Basilichthys microlepidotus (Jenyns) (Teleostei: atherinopsidae) in the Maipo River basin,central Chile

Freshwater systems are one of the environments most impacted by human activity, with pollution being a highly important factor. In Chile, several rivers exhibit varied levels of pollution, one of which is the Maipo River basin where the city of Santiago is located. The silverside Basilichthys microlepidotus (Jenyns) is an endemic fish species that inhabits this basin, thus we hypothesized that pollution has affected gene diversity and migration in populations of B. microlepidotus from the Maipo River basin. The aim of this study was to identify the population structure of B. microlepidotus in this basin and to determine if the populations of the silverside inhabiting polluted sites present differences in gene diversity and gene flow compared to populations inhabiting non-polluted areas. Using the variability of eight microsatellites, five populations of silverside were detected; three inhabiting non-polluted sites and two inhabiting polluted sites. From this, it was inferred that B. microlepidotus has been able to tolerate pollution in the Maipo River basin. No differences in gene diversity or migration were detected between polluted and non-polluted sites but comparison with historical estimation revealed an increase in the current migration rate when all the data from the basin were compared. A reduction in current effective population size was also observed when compared to historical values, and this is probably due to river degradation. Despite the disappearance of other fish species recorded at this basin, our results suggest that B. microepidotus is tolerant to pollution, thus indicating that native species respond differently to this environmental factor.     

Glutathione-S-transferase as a molecular biomarker of the state of marine organisms influenced by anthropogenic pressure

The activity of glutathione-S-transferase (GST), a key phase II enzyme catalyzing the biotrans-formation of organic electrophilic compounds, was studied in the bivalve Crenomytilus grayanus, the mysid shrimp Neomysis mirabilis, and the flounder Liopsetta pinnifasciata from Peter the Great Bay, Sea of Japan. GST activity was increased in fish and mollusks from polluted areas of the bay, compared to background areas. In mysid shrimps, pollution caused inhibition of the activity of this enzyme. The role of GST in adaptation processes of different species to the current level of pollution is discussed.     

Seafood Substitutions Obscure Patterns of Mercury Contamination in Patagonian Toothfish (Dissostichus eleginoides) or “Chilean Sea Bass”

Seafood mislabeling distorts the true abundance of fish in the sea, defrauds consumers, and can also cause unwanted exposure to harmful pollutants. By combining genetic data with analyses of total mercury content, we have investigated how species substitutions and fishery-stock substitutions obscure mercury contamination in Patagonian toothfish (Dissostichus eleginoides), also known as “Chilean sea bass”. Patagonian toothfish show wide variation in mercury concentrations such that consumers may be exposed to either acceptable or unacceptable levels of mercury depending on the geographic origins of the fish and the allowable limits of different countries. Most notably, stocks of Patagonian toothfish in Chile accumulate significantly more mercury than stocks closer to the South Pole, including the South Georgia/Shag Rocks stock, a fishery certified by the Marine Stewardship Council (MSC) as sustainably fished. Consistent with the documented geography of mercury contamination, our analysis showed that, on average, retail fish labeled as MSC-certified Patagonian toothfish had only half the mercury of uncertified fish. However, consideration of genetic data that were informative about seafood substitutions revealed a complex pattern of contamination hidden from consumers: species substitutions artificially inflated the expected difference in mercury levels between MSC-certified and uncertified fish whereas fishery stock substitutions artificially reduced the expected difference in mercury content between MSC-certified and uncertified fish that were actually D. eleginoides. Among MSC-certified fish that were actually D. eleginoides, several with exogenous mtDNA haplotypes (i.e., not known from the certified fishery) had mercury concentrations on par with uncertified fish from Chile. Overall, our analysis of mercury was consistent with inferences from the genetic data about the geographic origins of the fish, demonstrated the potential negative impact of seafood mislabeling on unwanted mercury exposure for consumers, and showed that fishery-stock substitutions may expose consumers to significantly greater mercury concentrations in retail-acquired fish than species substitutions.     

Microbial Diversity and Parasitic Load in Tropical Fish of Different Environmental Conditions

In this study we analysed fecal bacterial communities and parasites of three important Indonesian fish species, Epinephelus fuscoguttatus, Epinephelus sexfasciatus and Atule mate. We then compared the biodiversity of bacterial communities and parasites of these three fish species collected in highly polluted Jakarta Bay with those collected in less polluted Indonesian areas of Cilacap (E. sexfasciatus, A. mate) and Thousand Islands (E. fuscoguttatus). In addition, E. fuscoguttatus from net cages in an open water mariculture facility was compared with free living E. fuscoguttatus from its surroundings. Both core and shared microbiomes were investigated. Our results reveal that, while the core microbiomes of all three fish species were composed of fairly the same classes of bacteria, the proportions of these bacterial classes strongly varied. The microbial composition of phylogenetically distant fish species, i.e. A. mate and E. sexfasciatus from Jakarta Bay and Cilacap were more closely related than the microbial composition of more phylogentically closer species, i.e. E. fuscoguttatus, E. sexfasciatus from Jakarta Bay, Cilacap and Thousand Islands. In addition, we detected a weak negative correlation between the load of selected bacterial pathogens, i.e. Vibrio sp. and Photobacterium sp. and the number of endoparasites. In the case of Flavobacterium sp. the opposite was observed, i.e. a weak positive correlation. Of the three recorded pathogenic bacterial genera, Vibrio sp. was commonly found in E. fuscoguttatus from mariculture, and lessly in the vicinity of the net cages and rarely in the fishes from the heavily polluted waters from Jakarta Bay. Flavobacterium sp. showed higher counts in mariculture fish and Photobacteria sp. was the most prominent in fish inside and close to the net cages.     

“Pig in a poke (gato por liebre)”: The “mota” (Calophysus macropterus) Fishery,Molecular Evidence of Commercialization in Colombia and Toxicological Analyses

Overfishing has affected the population abundance trends of many commercial fish species. In the Amazon, the fishery of a catfish commonly known as “mota” or “piracatinga” (Calophysus macropterus) has become an important economic activity in the region as this species has replaced a number of other overexploited great catfish species in the markets. Due to this high exploitation, ways in which to increase captures have been identified. One strategy is to use decomposing animal carcasses as bait. Such strategy has increased the hunting pressure on endangered species such as caimans and river dolphins. We investigated which catfish species are currently commercialized in Colombian fish markets using DNA barcoding, and measured mercury concentration in the tissues of fish molecularly identified as C. macropterus. We collected 86 fish samples in markets of four Colombian cities. Sixty-eight of these were identified molecularly as C.macropterus. The mercury concentration of 29 such samples was analyzed. Samples presented total Hg concentrations higher than the limit for human consumption established by the WHO (0.5 μg/g). These results are worrisome and suggest that (1) C. macropterus is a widely used fish species for human consumption in Colombia and (2) C. macropterus has high concentrations of total Hg, making its consumption a public health risk. Results presented here suggest that C. macropterus has replaced capaz in most Colombian markets. This fishery threatens wild species of river dolphins and caimans, and is also a public health risk given the high mercury levels we found in a subsample of these fishes.     

Exposure to waterborne copper and high temperature induces the formation of reactive oxygen species and causes mortality in the Amazonian fish <Emphasis Type="Italic">Hoplosternum littorale</Emphasis>

Hoplosternum littorale is an Amazon fish that lives in urban areas surrounded by polluted igarapés, where elevated copper concentrations eventually occur. The central goal of this study was to evaluate the associated effects of high temperature and copper contamination on survival time and biochemical responses of the Amazonian fish species H. littorale. We exposed fish to two nominal dissolved copper concentrations (50 and 500 µg l^?1) and combined temperatures of 28 and 34°C. Our findings showed that the combination of these variables affects the survival time of this species. The activity of the biotransformation enzymes ethoxyresorufin-O-deethylase and glutathione-S-transferase showed no alterations in fish within all treatments. The increase of reactive oxygen species and the decrease in potential total antioxidant capacity promoted the imbalance in the antioxidant system. An induction in superoxide dismutase activity occurred in fish exposed to copper concentrations of 50 and 500 µg l^?1 at both temperatures, suggesting liver impairments. Thus, we suggest that H. littorale is sensitive to copper, and this sensitivity is increased further with exposure to high temperatures, particularly in the survival time and reactive oxygen species formation of this fish species.     

Genetic variation in two land snails, Cepaea nemoralis and Succinea putris (Gastropoda, Pulmonata), from sites differing in heavy metal content

Allozyme variation was determined in two land snail species (Cepaea nemoralis and Succinea putris) from four localities in northern Belgium. In each locality we selected a polluted and a nearby, less-polluted, reference plot. We examined whether (i) genetic variability differed between the polluted and reference plots, (ii) populations from polluted plots experienced recent bottlenecks, and (iii) certain allele or genotype frequencies were associated with the pollution. Our results suggest that (i) about 13% of the genetic differentiation in C. nemoralis and 5% in S. putris was due to differences among polluted and reference plots, (ii) polluted and reference plots had comparable levels of genetic variation, but in C. nemoralis observed heterozygosities were higher in polluted plots, (iii) most plots showed significant evidence for recent bottlenecks, irrespective of the degree of pollution, so that bottlenecks seem poor indicators of pollution-induced stress in land snails, and (iv) mutagenic or pollution-induced modifications did not seem to account for new allozyme variants in polluted sites. The observed patterns of genetic variation may be explained by the action of genetic drift, pollution-mediated selection, restricted gene flow, or a combination of these processes.     

Fate and distribution of toxic heavy metals in some marine organisms from the eastern Adriatic coast

The paper reports on levels of heavy metals in some organisms from the eastern Adriatic coast and polluted areas near a big urban centre (Split area). Surprisingly high Hg and MeHg concentrations were found in sea bream (Pagellus erythrinus) and striped mullet (Mullus barbatus) from the south-eastern part of the Adriatic. The reason for the high levels are probably geochemical anomalies. Studies of total and organic mercury content in bivalves have also shown that the gills and hepatopancreas had high levels of accumulated mercury. Our results have shown that fish contain significantly higher concentrations of MeHg than mussel. High concentrations of these elements in fish may be a consequence of the methylation process in the visceral organs. Bacterial activity in the intestinal contents is most likely to be responsible for this methylation (Rudd et al., 1980).     

Study on impact of habitat degradation on proximate composition and amino acid profile of Indian major carps from different habitats

This investigation is aimed to study an impact of habitat degradation on proximate composition and amino acid (AAs) profile of Catla catla, Labeo rohita and Cirrhinus mrigala collected from polluted, non-polluted area (upstream) and a commercial fish farm. The amino acid profile was estimated by the amino acid analyzer. C. catla collected from the polluted environment had highest lipid, protein and ash contents (12.04?±?0.01, 13.45?±?0.01 and 0.93?±?0.03%, respectively). The high protein content (14.73?±?0.01 and 14.12?±?0. 01%) was recorded in C. catla procured from non-polluted (upstream) wild habitat of River Chenab and controlled commercial fish farm. Farmed fish species showed comparatively higher moisture contents followed by upstream and polluted area fishes. C. mrigala showed significant differences in amino acid and proximate composition collected from a polluted site of the river Chenab. C. catla collected from non-polluted site of the river showed an excellent nutrient profile, followed by L. rohita (wild and farmed) and C. mrigala (polluted area), respectively. All fishes from the polluted areas of the River Chenab indicated a significant decrease in the concentration of some AAs when compared to farmed and wild (upstream) major carps. Omitting of some important AAs was also observed in the meat of fish harvested from polluted habitat of this river. C. mrigala and L. rohita exhibited a significant increase in the concentration of some of non-essential amino acids such as cysteine in their meat. The results indicated that wild fish (upstream) and farmed fish species had highest protein contents and amino acid profile and hence appeared to be the best for human consumption. The proximate composition and AAs profiles of fish harvested from the polluted area of the river clearly indicated that efforts shall be made for the restoration of habitat to continue the requirement of high quality fish meat at a low cost to the human population.     

The use of fish metabolic, pathological and parasitological indices in pollution monitoring

  An integrated biological effect monitoring concept has been tested in flounder (Platichthys flesus L.) from four locations with different anthropogenic impact in the German Bight. During 3 years of sampling, biomarkers at all levels of biological organisation from the molecular to the ecosystem level were applied and tested on 742 individual fish of body lengths between 18 and 25 cm. At the ecosystem level, the fish were taken as a habitat for the parasite assemblage. The hypothesis was that changes in the environment might lead to changes in the species diversity of parasites and in the infection intensity of single species, as well as between heteroxenic and monoxenic parasite species (H/M ratio). At the molecular level, activity of the CYP1A-dependent monooxygenase ethoxyresorufin O-deethylase (EROD) was used as a biomarker of exposure. At the subcellular level, the integrity of lysosomal membranes in hepatocytes was taken as an indicator of non-specific acute and chronic toxic effects. Both biomarkers are recommended by the ICES Advisory Committee on the Marine Environment for the application in biological effects monitoring programmes. In addition, neutral lipid content in the liver was used as a marker for pathologically induced fat accumulation. In the same individual fish, a new method for the measurement of macrophage aggregate activity in the liver was tested for its application and reliability in reflecting immunosuppression. Tests were accompanied by chemical analysis of standard organochlorine and heavy metal residues in flounder tissue. A total of 33 parasite species were found. As an indicator species, the mean abundance of Trichodina sp. reflected best the pollution gradient observed with highest infection intensity at the most polluted location. Species diversity was significantly higher in fish caught near the reference site and significantly lower in fish from the polluted Elbe estuary. The use of the heteroxenous/monoxenous species ratio as a marker was not useful at the locations investigated because of the dominance of heteroxenous species at all habitats. Since EROD activity and macrophage aggregate activity were dependent on sex and maturity of female flounder, only male fish were taken into consideration for the integrated evaluation of data. All biochemical and histochemical tests were able to reflect accurately the site-specific differences, as well as an observed pollution event at the end of 1995 as determined by chemical analyses. The correlation analysis revealed a connection not only between the single parasitological and biochemical parameters but also within these groups. The non-specific immune response and Trichodina infection intensity were correlated with all other parameters, leading to the assumption that these may serve as links between the lowest and the highest levels of biological organisation. The simultaneous use of metabolic and parasitological results facilitated the interpretation of the observed variations of the data and the distinction between natural variation and pollution-mediated effects. Received: 1 March 1999 / Received in revised form: 25 May 1999 / Accepted: 7 June 1999     

A dynamic integrated model for mercury bioaccumulation in marine organisms

A novel integrated dynamic model, the Integrated Fish Model (INTFISH), incorporating mercury (Hg) dynamics at non-steady state in marine organisms, is presented and is applied to the benthic food web in a polluted area. The integrated Fish model represents the dynamics of inorganic mercury (Hg^II) and methyl‑mercury (MeHg) in a real marine ecosystem including environmental (seawater and sediments) and biota compartments. Mercury concentration in fish is estimated using the INTFISH model coupled, in real-time, with results from i) the seawater and sediments modules computed using the HR3DHG model, ii) a dedicated Phytoplankton model and iii) six modules for Hg fluxes within the invertebrate compartment, incorporating the main organisms included in fish diet preferences, whose variations during the whole life cycle are also taken into account to verify the sensitivity of the integrated model to the core set of parameters. The simulated total mercury concentrations (Hg^TOT) in specimens of red mullet (Mullus barbatus), selected as target species for the Fish model, are in excellent agreement with field observations reported from the investigated area. The intrinsic modularity of the model offers the opportunity to extend simulations to other fish species (which are part of the diet of human populations of interest) and predict Hg concentration in food. A natural extension of the model will allow to evaluate the health risks related to human consumption of contaminated fish.     

Selenium detected in fish otoliths: a novel tracer for a polluted lake?

To test if otoliths can be used to track fish migration in polluted areas, fish sampled from Onondaga Lake, heavily polluted with mercury, were used in an assay to determine whether mercury was detectable in the fishes’ otoliths using synchrotron-based scanning X-ray fluorescence microscopy (SXFM). Mercury was undetectable, but selenium, rarely reported in otoliths and known as a physiological antagonist to mercury, was. Strontium was also present but appeared to be taken up independently of selenium, and thus these serve as independent biogeochemical markers. Both selenium and mercury were detected in fish tissues, but selenium was below levels considered toxic. Selenium was low in otoliths of fishes collected in nearby Oneida Lake. Synoptic surveys of water chemistry revealed that Se is regionally highest in Onondaga Lake and in particular its main inlet, Onondaga Creek. SXFM appears to be a sensitive method for detecting selenium in otoliths.     

Interrelationships between bioaccumulation of organic trace pollutants (PCBs,organochlorine pesticides and PAHs), and MFO-induction in fish

• 1.1. Hydrophobic compounds that are more easily biotransformed (e.g. PAHs) generally show less bioaccumulation in fish than the more persistent PCBs and DDTs.
• 2.2. In lake Nieuwe Meer, with the highest levels of organic micropollutants, the hepatic MFO activity was elevated in three fish species. This indicates that MFO activity might be a sensitive indicator for organic micropollutants in the aquatic environment.
• 3.3. Activities of the 3-MC type inducible isozymes were most pronounced in all three fish species studied. Though further research is required, indications for the existence of a PB-type inducible enzyme system have been demonstrated for two fish species, i.e. pike and eel.
• 4.4. Fish liver enlargement as a consequence of MFO induction could not be demonstrated in fish from the most polluted lake.
• 5.5. In fish, a correlation was observed between PCB or OCP tissue concentrations on the one hand, and hepatic MFO activities on the other. The low PAH fish/sediment ratios are further reduced when MFO systems are induced due to organic micropollution. The interrelationship between bioaccumulation and enzyme induction demonstrates the importance of an integrated study of these phenomena in field research.

     

First Description of Various Bacteria Resistant to Heavy Metals and Antibiotics Isolated from Polluted Sites in Tunisia

Environmental bacteria belonging to various families were isolated from polluted water collected from ten different sites in Tunisia. Sites were chosen near industrial and urban areas known for their high degree of pollution. The aim of this study was to investigate cross-resistance between heavy metals (HM), i.e., silver, mercury and copper (Ag, Hg, and Cu), and antibiotics. In an initial screening, 80 isolates were selected on ampicillin, and 39 isolates, retained for further analysis, could grow on a Tris-buffered mineral medium with gluconate as carbon source. Isolates were identified based on their 16S rRNA gene sequence. Results showed the prevalence of antibiotic resistance genes, especially all isolates harbored the bla_TEM gene. Some of them (15.38%) harbored bla_SHV. Moreover, several were even ESBLs and MBLs-producers, which can threaten the human health. On the other hand, 92.30%, 56.41%, and 51.28% of the isolates harbored the heavy metals resistance genes silE, cusA, and merA, respectively. These genes confer resistance to silver, copper, and mercury. A cross-resistance between antibiotics and heavy metals was detected in 97.43% of our isolates.     

Concentration of Zinc,Copper, Iron,Calcium, and Magnesium in the Serum,Tissues, and Urine of Streptozotocin-Induced Mild Diabetic Rat Model

A survey carried out in Lake Tana in 2015 found that Hg levels in some fish species exceeded internationally accepted safe levels for fish consumption. The current study assesses human exposure to Hg through fish consumption around the Lake Tana. Of particular interest was that a dietary intake of fishes is currently a health risk for Bihar Dar residents and anglers. Hair samples were collected from three different groups: anglers, college students and teachers, and daily laborers. A questionary includes gender, age, weight, activity. Frequency of fish consumption and origin of the eaten fish were completed by each participant. Mercury concentrations in hair were significantly higher (P value <0.05) for anglers (mean?±?standard deviation 0.120?±?0.199 μg/g) than college students (mean?±?standard deviation 0.018?±?0.039 μg/g) or daily workers (mean?±?standard deviation 16?±?9.5 ng/g). Anglers consumed fish more often than daily workers and college group. Moreover, there was also a strong correlation (P value <0.05) between the logarithms of total mercury and age associated with mercury concentration in scalp hair. Mercury concentrations in the hair of men were on average twice the value of the women. Also, users of skin lightening soap on a daily basis had 2.5 times greater mercury in scalp hair than non-users. Despite the different sources of mercury exposure mentioned above, the mercury concentrations of the scalp hair of participants of this study were below levels deemed to pose a threat to health.     

Effects of habitat alteration caused by petrochemical activities and oil spills on the habitat use and interspecific relationships among four species of Afrotropical freshwater turtles

The large-scale effects of habitat alteration produced by oil-industry related pollution on the habitat use of four species of freshwater turtles (Pelusios castaneus, Pelusios niger, Pelomedusa subrufa, Trionyx triunguis) were studied in the River Niger Delta, southern Nigeria (West Africa) between 1996 and 2004. The numbers of turtle specimens observed during our study declined drastically in polluted sites, despite a nearly identical field effort. The number of specimens of all turtle species declined considerably at all habitat types, but complete disappearance in polluted areas was found only with regard to one habitat type for Trionyx triunguis and two habitat types for Pelomedusa subrufa. The mean values of species dominance and diversity indexes were not statistically significant between pristine and altered areas. Based on the interspecific similarity in proportional frequencies of turtle specimens found in each habitat type, a multivariate set of analyses (UPGMA) showed that the turtles were arranged in three ‘ecological’ clusters: a group formed by Pelomedusa subrufa at both polluted and unpolluted areas and Trionyx triunguis at polluted areas; (ii) a group formed by Pelusios castaneus in polluted areas and Pelusios niger in polluted areas; (iii) a group formed by Pelusios castaneus in unpolluted areas and Pelusios niger in unpolluted areas; however, this latter cluster was not very close, as the linkage distance was close to 80% of Euclidean distance. Habitat use similarity among turtles in both polluted and unpolluted study areas was evaluated by the use of two types of overlap formulas (Pianka and Czechanowski) and the use of Monte Carlo randomisations in order to control for the eventual role of chance in the actual data matrix. These data indicated that, for a pair of species (Pelusios niger vs. Pelusios castaneus), there was a statistically significant increase in the similarity of habitat use in the polluted areas vs. the unpolluted areas, and that this pattern was not dependent on the chance. Considering that these two species are ecologically and morphologically similar, we conclude that the most likely consequence at the community level is an increase in the intensity of interspecific competition for space between Pelusios niger and Pelusios castaneus in the polluted areas. Although the direction of the intensification of this competition process could not be easily predicted, it is likely that the species which is least adapted to life in main rivers and creeks may be disadvantaged over the other competitor. The general implications for habitat preservation are also discussed.     

Selenium and mercury concentrations in some fish species of the Madeira River, Amazon Basin, Brazil

Samples of 7 species of piscivorous, omnivorous, and herbivorous fish caught at 12 different sites on the Madeira River, Amazon Basin, were analyzed for selenium and mercury. Selenium was determined by anodic stripping voltammetry and mercury by cold vapor atomic absorption spectrophotometry. The means for selenium concentrations ranged from 0.49 to 3.11 nmol/g and for mercury from 0.41 to 6.66 nmol/g depending on the fish species. The molar ratios of Hg:Se increased according to the fish trophic level. Piscivorous species had the highest mean ratio (4.0) and herbivorous species the lowest (0.9). There was a positive and statistically significant correlation between selenium and mercury concentrations for the herbivorous species (r = 0.716;p = 0.0088) not seen for omnivororus and piscivorous species (r = -0.2032;p = 0.3407). These findings are significant for the fish-eating population of the Madeira River because the ingestion of mercury would always be in excess of selenium.     

The use of Cerastoderma glaucum as a sentinel and bioindicator species: Take-home message

Bivalves are frequently used to assess environmental contamination, and are often considered good sentinel and/or bioindicator species. For that reason the bioaccumulation and toxicity induced by metals and As in the cockle Cerastoderma glaucum, collected from areas with different contamination levels along the Óbidos lagoon (Portugal), were used to evaluate the use of this species as sentinel and/or bioindicator. The results showed that areas in the middle of the lagoon presented lower metals and As concentrations, lower total organic matter content and lower percentage of fine particles than areas in the Bom Sucesso arm. In all areas Cr, Pb and Cu were the most abundant elements, while Ni, As, Cd and Hg were less abundant. Results also showed a moderate correlation between total elements concentrations found in C. glaucum and in sediment, and thus caution should be taken when considering this species as a good sentinel species. The present study also revealed that, in general, C. glaucum from areas in the middle of the lagoon accumulated higher concentrations of metals and As (Biota-Sediment Accumulation Factor >1) than cockles from the most polluted areas located in the Bom Sucesso arm. However, in all areas, the majority of metals (Cu, Cr, Pb) were found in cockles insoluble fraction which may explain low cellular damage and reduced oxidative stress responses observed. Therefore, our results may further alert for caution when identifying C. glaucum as a good bioindicator species. Thus, our findings highlight the fact that studies should be cautious when selecting species for environmental monitoring, since good sentinels or bioindicators in highly polluted systems may not act in the same way in low or moderately contaminated areas. Furthermore, our study warns for the misclassification of cockles in different ecosystems.