Acute effects of mercuric chloride on the olfactory epithelium of Trichomycterus brasiliensis

Multi biomarker approach to assess manganese and manganese nanoparticles toxicity in Pangasianodon hypophthalmus

Manganese (Mn) is an essential element for humans and animals including, fish. It is a still poorly studied in aquatic organisms, where it can be noticeably useful for dietary components and also found pollutant in aquatic environment at high concentrations. On the above information, an experiment was delineated to determine the lethal concentration of manganese (Mn) and manganese nanoparticles (Mn-NPs) alone and with high temperature (34 °C) and its effect on various biochemical markers in Pangasianodon hypophthalmus. The median lethal concentration (96-LC₅₀) of Mn alone (111.75 mg L^-1) and along with high temperature (110.76 mg L^-1), Mn-NPs alone (93.81 mg L^-1) and with high temperature (34 °C) (92.39 mg L^-1) was determined in P. hypophthalmus. The length and weight of the fish were 6.32 ± 0.23 cm and 7.57 ± 1.35 g. The present investigation used five hundred forty-six fish, including range finding (216 fish) and definitive test (330 fish). The acute definitive doses were applied to assess the effect of oxidative stress, glycolytic biomarkers, protein biomarkers, fish immunity, neurotransmitter, energy level, stress hormone and histopathology. Oxidative stress (catalase, superoxide dismutase, glutathione-s-transferase and glutathione peroxidase), stress biomarkers (lipid peroxidation, cortisol, heat shock protein, and blood glucose), lactate and malate dehydrogenase, alanine and aspartate aminotransferase, a neurotransmitter, glucose-6-phosphate dehydrogenase (G6PDH), ATPase, immune system biomarkers (NBT, total protein, albumin, globulin and A:G ratio) were altered with exposure to Mn and Mn-NPs. The histopathology of the liver and gill were also changed due to exposure to Mn and Mn-NPs. The bioaccumulation of Mn in the liver, gill, kidney, brain and muscle tissues, and experimental water at different intervals of 24, 48, 72 and 96 h were determined. Based on the present results, it is strongly suggested that Mn and Mn-NPs exposure alone and with high temperature (34 °C) enhanced toxicity and altered biochemical and morphological attributes. This study also suggested that essential elements in both forms (inorganic and nano) at higher concentrations of Mn and Mn-NPs lead to pronounced deleterious alteration in cellular and metabolic activities and histopathology of P. hypophthalmus.

Response of Olfactory Sensory Neurons to Mercury Ions in Zebrafish: An Immunohistochemical Study

Olfactory sensory neurons (OSNs) of fish belong to three main types: ciliated olfactory sensory neurons (cOSNs), microvillous olfactory sensory neurons (mOSNs), and crypt cells. Mercury is a toxic metal harmful for olfaction. We exposed the olfactory epithelium of zebrafish to three sublethal Hg2+ concentrations. Molecular markers specific for the different types of OSNs were immunohistochemically detected. Image analysis of treated sections enabled counting of marked cells and measurement of staining optical density indicative of the response of OSNs to Hg2+ exposure. The three types of OSNs reacted to mercury in a different way. Image analysis revealed that mOSNs are more susceptible to Hg2+ exposure than cOSNs and crypt cell density decreases. Moreover, while the ratio between sensory/nonsensory epithelium areas is unchanged, epithelium thickness drops, and dividing cells increase in the basal layer of the olfactory epithelium. Cell death but also reduction of apical processes and marker expression could account for changes in OSN immunostaining. Also, the differential results between dorsal and ventral halves of the olfactory rosette could derive from different water flows inside the olfactory chamber or different subpopulations in OSNs.

Neurobehavioral and immune-toxic impairments induced by organic methyl mercury dietary exposure in Nile tilapia Oreochromis niloticus

Although substantial knowledge of mercury toxicity in fish has been assembled; until now, studies investigating the toxic impacts in Nile tilapia (Oreochromis niloticus) following dietary exposure to organic methyl mercury (MeHg) are less prolific. Accordingly, the current study aimed to evaluate the impacts of MeHg on neurobehavioral and immune integrity in Nile tilapia after dietary exposure. Two hundred and twenty-five juvenile Nile tilapia (19.99 ± 0.33 g) were allocated into five groups in triplicates (15 fish/replicate). G1, G2, G3, G4, and G5. O. niloticus were fed corresponding basal diets containing 0, 0.5, 1, 1.5, and 2 mg/kg diet MeHg chloride (MeHgCl) daily for 30 days, zero value represented the control G1 group. The results showed that MeHg induced significant alterations in O. niloticus behavior, the swimming behavior was significantly decreased, while scratching, biting, and fin tugging behaviors were significantly augmented. Moreover; chasing, mouth pushing, and butting behaviors were significantly increased in all the exposed groups. MeHg significantly decreased brain acetylcholine esterase (AChE) and serum immunoglobulin M (IgM) levels in all the exposed groups. Meanwhile, serum levels of lysozyme (LYZ), nitric oxide (NO), superoxide dismutase (SOD) malondialdehyde (MDA), protein carbonyl (PCO), and 8 hydroxy 2 deoxyguanosine (8OH2dG) were significantly elevated in all the exposed groups except for serum reduced glutathione (GSH) content was significantly decreased implying oxidative stress (OS), lipid peroxidation (LPO), protein, DNA damage and impaired immune response of the exposed tilapia. MeHg significantly altered transcriptional expression of immune-related genes including (TNF-α, IL-1β, and IL-8, and IL-10) in all the exposed groups. From the obtained outcomes, the present research is the premier to investigate that dietary MeHg exposure in O. niloticus significantly induced neurobehavioral and immune defense impairments in a dose-related manner. This study exhibits that dietary MeHg may pose a potential threat to the O. niloticus populations.

A multidimensional concept for mercury neuronal and sensory toxicity in fish - From toxicokinetics and biochemistry to morphometry and behavior

BACKGROUND

Neuronal and sensory toxicity of mercury (Hg) compounds has been largely investigated in humans/mammals with a focus on public health, while research in fish is less prolific and dispersed by different species. Well-established premises for mammals have been governing fish research, but some contradictory findings suggest that knowledge translation between these animal groups needs prudence [e.g. the relative higher neurotoxicity of methylmercury (MeHg) vs. inorganic Hg (iHg)]. Biochemical/physiological differences between the groups (e.g. higher brain regeneration in fish) may determine distinct patterns. This review undertakes the challenge of identifying sensitive cellular targets, Hg-driven biochemical/physiological vulnerabilities in fish, while discriminating specificities for Hg forms.

SCOPE OF REVIEW

A functional neuroanatomical perspective was conceived, comprising: (i) Hg occurrence in the aquatic environment; (ii) toxicokinetics on central nervous system (CNS)/sensory organs; (iii) effects on neurotransmission; (iv) biochemical/physiological effects on CNS/sensory organs; (v) morpho-structural changes on CNS/sensory organs; (vi) behavioral effects. The literature was also analyzed to generate a multidimensional conceptualization translated into a Rubik's Cube where key factors/processes were proposed.

MAJOR CONCLUSIONS

Hg neurosensory toxicity was unequivocally demonstrated. Some correspondence with toxicity mechanisms described for mammals (mainly at biochemical level) was identified. Although the research has been dispersed by numerous fish species, 29 key factors/processes were pinpointed.

GENERAL SIGNIFICANCE

Future trends were identified and translated into 25 factors/processes to be addressed. Unveiling the neurosensory toxicity of Hg in fish has a major motivation of protecting ichtyopopulations and ecosystems, but can also provide fundamental knowledge to the field of human neurodevelopment.

Contaminant-induced oxidative stress in fish: a mechanistic approach

The presence of reactive oxygen species (ROS) in living organisms was described more than 60 years ago and virtually immediately it was suggested that ROS were involved in various pathological processes and aging. The state when ROS generation exceeds elimination leading to an increased steady-state ROS level has been called "oxidative stress." Although ROS association with many pathological states in animals is well established, the question of ROS responsibility for the development of these states is still open. Fish represent the largest group of vertebrates and they inhabit a broad range of ecosystems where they are subjected to many different aquatic contaminants. In many cases, the deleterious effects of contaminants have been connected to induction of oxidative stress. Therefore, deciphering of molecular mechanisms leading to such contaminant effects and organisms' response may let prevent or minimize deleterious impacts of oxidative stress. This review describes general aspects of ROS homeostasis, in particular highlighting its basic aspects, modification of cellular constituents, operation of defense systems and ROS-based signaling with an emphasis on fish systems. A brief introduction to oxidative stress theory is accompanied by the description of a recently developed classification system for oxidative stress based on its intensity and time course. Specific information on contaminant-induced oxidative stress in fish is covered in sections devoted to such pollutants as metal ions (particularly iron, copper, chromium, mercury, arsenic, nickel, etc.), pesticides (insecticides, herbicides, and fungicides) and oil with accompanying pollutants. In the last section, certain problems and perspectives in studies of oxidative stress in fish are described.

Brain as a critical target of mercury in environmentally exposed fish (Dicentrarchus labrax)--bioaccumulation and oxidative stress profiles

Although mercury is recognized as a potent neurotoxicant, information regarding its threat to fish brain and underlying mechanisms is still scarce. In accordance, the objective of this work was to assess vulnerability of fish to mercury neurotoxicity by evaluating brain pro-oxidant status in wild European sea bass (Dicentrarchus labrax) captured in an estuarine area affected by chlor-alkali industry discharges (Laranjo Basin, Ria de Aveiro, Portugal). To achieve this goal, brain antioxidant responses such as catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) activities and total glutathione (GSHt) content were measured. Additionally, damage was determined as lipid peroxidation. To ascertain the influence of seasonal variables on both mercury accumulation and oxidative stress profiles, surveys were conducted in contrasting conditions-warm and cold periods. In the warm period, brain of fish from mercury contaminated sites exhibited ambivalent antioxidant responses, viz. higher GR activity and lower CAT activity regarded, respectively, as possible signs of protective adaptation and increased susceptibility to oxidative stress challenge. Though the risk of an overwhelming ROS production cannot be excluded, brain appeared to possess compensatory mechanisms and was able to avoid lipid peroxidative damage. The warm period was the most critical for the appearance of oxidative damage as no inter-site alterations on oxidative stress endpoints were detected in the cold period. Since seasonal differences were found in oxidative stress responses and not in mercury bioaccumulation, environmental factors affected the former more than the latter. This work increases the knowledge on mercury neurotoxicity in feral fish, highlighting that the definition of critical tissue concentrations depends on environmental variables.

Mercury contamination in spotted seatrout, Cynoscion nebulosus: an assessment of liver, kidney, blood, and nervous system health

Marine fishes in South Florida (Florida Keys-Florida Bay-Everglades region) accumulate higher concentrations of mercury (Hg) in their tissues than similar fishes from other areas of the southeastern U.S., though it is not known whether these elevated levels affect fish health. In this study, we used quantifiable pathological and biochemical indicators to explore Hg-associated differences in marine fish from South Florida, where Hg contamination is high, and from Indian River Lagoon, Florida, which served as a reference area. Hg concentrations in all tissues of mature spotted seatrout (Cynoscion nebulosus) from South Florida were significantly higher than those from Indian River Lagoon and were within the threshold range of those in studies where effects of Hg exposure have been observed. The distribution of Hg among tissues followed the same trend in both areas, with the greatest concentration in kidney tissue, followed by liver, muscle, brain, gonad, and red blood cells. Blood-plasma biochemistry showed that concentrations of iron, inorganic phosphate, lactate dehydrogenase, and aspartate aminotransferase were significantly less in South Florida. Also, fructosamine and alkaline phosphatase were significantly less in South Florida. Liver histology revealed that pyknosis/necrosis, interstitial inflammation, and bile duct hyperplasia were found only in seatrout from South Florida, and steatosis/glycogen was more frequently found in Indian River Lagoon specimens. In renal tissue, interstitial inflammation, glomerular dilatation and thickening, and tubular degeneration and necrosis were more frequently found in South Florida specimens. Changes in the liver cytoskeleton and morphology may explain some of the differences in blood parameters between study areas. Neurochemical analyses showed that brain N-methyl-d-aspartic acid (NMDA) receptors (but not those of muscarinic cholinergic receptors, monoamine oxidase, or acetylcholinesterase) were significantly less in fish from South Florida than from Indian River Lagoon. These findings provide compelling evidence that elevated Hg could cause quantifiable pathological and biochemical changes that might influence the health of spotted seatrout and could also affect other marine fish species.

Antioxidant system breakdown in brain of feral golden grey mullet (Liza aurata) as an effect of mercury exposure

Although brain has been recognized as a primary target for mercury toxicity in mammals, the effects of this metal in fish brain are scarcely described. Thus, the main objective of this study was to assess the mercury threat to feral fish (Liza aurata) by estimating the antioxidant defenses and peroxidative damage in brain, keeping in mind the association with mercury accumulation. Sampling was carried out in an estuarine area historically affected by discharges from a chlor-alkali industry-Laranjo Basin (Ria de Aveiro, Portugal). Total mercury (T-Hg) in brain increased towards the contamination source, clearly indicating mercury exposure. An overall antioxidant depletion was verified in brain of fish collected at the mercury-contaminated stations, since total glutathione content and the studied antioxidant enzymes (catalase-CAT, glutathione peroxidase-GPx, glutathione-S-transferase-GST and glutathione reductase-GR) significantly decreased. In addition, this breakdown of the redox-defense system was significantly correlated with the accumulated T-Hg levels. Unexpectedly, fish exhibited unaltered lipid peroxidation levels, pointing out a higher propensity of mercury to inhibit enzymes than to oxidatively damage lipids in the brain. Nevertheless, an increased susceptibility of the fish's brain was identified, leaving the organ more vulnerable to oxidative stress-related challenges. Overall, the current findings provide information to better understand mechanisms of mercury neurotoxicity in fish.

Developmental selenomethionine and methylmercury exposures affect zebrafish learning

Methylmercury (MeHg) is a ubiquitous environmental pollutant and has been shown to affect learning in vertebrates following relatively low exposures. Zebrafish were used to model long-term learning deficits after developmental MeHg exposure. Selenomethionine (SeMet) co-exposure was used to evaluate its role in neuroprotection. Embryos were exposed from 2 to 24h post fertilization to (1) MeHg without SeMet, (2) SeMet without MeHg and (3) in combination of MeHg and SeMet. In case (1), the levels of MeHg were 0.00, 0.01, 0.03, 0.06, 0.10, and 0.30 microM. In case (2), the levels of SeMet were 0.00. 0.03, 0.06, 0.10, and 0.30 microM. In case (3), co-exposure levels of (MeHg, SeMet) were (0.03, 0.03), (0.03, 0.06), (0.03, 0.10), (0.03, 0.30), (0.10, 0.03), (0.10, 0.06), (0.10, 0.10), and (0.10, 0.30) microM. Learning functions were tested in individual adults, 4 months after developmental exposure using a spatial alternation paradigm with food delivery on alternating sides of the aquarium. Low levels of MeHg (<0.1 microM) exposure delayed learning in treated fish; fish exposed to higher MeHg levels were unable to learn the task; SeMet co-exposure did not prevent this deficit. These data are consistent with findings in laboratory rodents. The dorsal and lateral telencephalon are the primary brain regions in fish involved in spatial learning and memory. Adult telencephalon cell body density decreased significantly at all MeHg exposures >0.01 microM MeHg. SeMet co-exposure ameliorated but did not prevent changes in telencephalon cell body density. In summary, MeHg affected both learning and brain structure, but SeMet only partially reversed the latter.

Acute effects of copper and mercury on the estuarine fish Pomatoschistus microps: linking biomarkers to behaviour

The main objective of the present study was to investigate possible links between biomarkers and swimming performance in the estuarine fish Pomatoschistus microps acutely exposed to metals (copper and mercury). In independent bioassays, P. microps juveniles were individually exposed for 96 h to sub-lethal concentrations of copper or mercury. At the end of the assays, swimming performance of fish was measured using a device specially developed for epibenthic fish (SPEDE). Furthermore, the following biomarkers were measured: lipid peroxidation (LPO) and the activity of the enzymes acetylcholinesterase (AChE), lactate dehydrogenase (LDH), glutathione S-transferases (GST), 7-ethoxyresorufin-O-deethylase (EROD), superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GPx). LC(50)s of copper and mercury (dissolved throughout metal concentrations) at 96h were 568 microg L(-1), and 62 microg L(-1), respectively. Significant and concentration-dependent effects of both metals on swimming resistance and covered distance against water flow were found at concentrations equal or higher than 50 microg L(-1) for copper and 3 microg L(-1) for mercury (dissolved throughout metal concentrations). These results indicate that SPEDE was efficacious to quantify behavioural alterations in the epibenthic fish P. microps at ecologically relevant concentrations. Significant alterations by both metals on biomarkers were found including: inhibition of AChE and EROD activities, induction of LDH, GST and anti-oxidant enzymes, and increased LPO levels, with LOEC values ranging from 25 to 200 microg L(-1), for copper and from 3 to 25 microg L(-1) for mercury (dissolved throughout metal concentrations). Furthermore, significant and positive correlations were found between some biomarkers (AChE and EROD) and behavioural parameters, while negative correlations were found for others (LPO, anti-oxidant enzymes and LDH) suggesting that disruption of cholinergic function through AChE inhibition, decreased detoxification capability due to EROD inhibition, additional energetic demands to face chemical stress, and oxidative stress and damage may contribute to decrease the swimming performance of fish. Since a reduced swimming capability of fish may reduce their ability to capture preys, avoid predators, and interfere with social and reproductive behaviour, the exposure of P. microps to copper and/or mercury concentrations similar to those tested here may decrease the fitness of wild populations of this species.

Effects of dietary methylmercury on liver and kidney histology in the neotropical fish Hoplias malabaricus

Methylmercury is a potent toxic present in Amazonian fish species due to gold mining activities. In the present work, we investigated the morphological effects of methylmercury in liver and kidney of Hoplias malabaricus feeding contaminated prey fish over 70 days. Two groups of nine mature fish (tested and control) were acclimatized for four weeks to laboratory conditions and then the tested group fed prey fish previously contaminated at an additional level of 0.075 microg MeHg g(-1) at 5-day intervals and over 14 successive intervals whereas control group fed uncontaminated fish. H. malabaricus specimens were then dissected for chemical and morphological analyses. The low and realistic level of MeHg in the prey fish induced a low increase of total mercury in liver (1.8-fold) and muscle (2.2-fold). The biomagnification factor (Hg in predator/Hg in prey) reached 142 in liver and 21 in muscle and was indicative of a relatively fast contamination of internal organs by dietary exposure. The liver of exposed individuals presented leukocyte infiltration, increased number of melano-macrophage centers, necrotic areas and lesions in Disse's space. Evident disorder and chaos in cytoskeleton organization suggest a strong toxic effect in hepatocytes, such as organelles positioning and movement, vesicles traffic and secretion. Head kidney showed large necrosis areas, increased number of melano-macrophages centers, phagocytic areas, intercellular space among parenquimal cells and atypical cells. Injuries and damages to tissues suggest too slow defense mechanisms to immobilize or eliminate ingested methylmercury, demonstrating that the sensitivity of fish cells to methylmercury exposure is higher than it has been previously described in the literature.

Rodlet cells and the sensory systems in zebrafish (Danio rerio)

This preliminary work was designed to study, using routine procedures for light and transmission electron microscopy, the presence of rodlet cells (RCs) in or near the sensory systems of 12 adult specimens (4.0 +/- 1.2 cm, LT +/- SD) of zebrafish, Danio rerio Hamilton, 1822. Rodlet cells, characterized by a distinctive cell cortex (range, 0.4-1.5 microm in thickness) and conspicuous inclusions named "rodlets," have a round to ovoid nucleus with irregular outline. Mature RCs are 11.5 +/- 1.2 microm (mean +/- SD) long and 7.8 +/- 1.1 microm (mean +/- SD) wide. These cells are more numerous near neuromasts enclosed by an epithelial roof and/or ossified canal wall. In contrast, very few RCs were noticed near superficial neuromasts. Based on the presence of RCs around the two cranial neuromasts of each fish, a variable number from 1 to 15 rodlet cells was found (10.4 +/- 3.6, mean +/- SD). The RCs were located 1.5 microm (minimal) to 73.3 microm (maximal) from the neuromast (27.9 +/- 17.2, mean +/- SD). Moreover, RCs were found in olfactory epithelium and in proximity to some taste buds. Interestingly, RCs were absent in the inner ear, eye, and brain.

Bioaccumulation and elimination of Hg in the fireworm Eurythoe complanata (Annelida: Polychaeta) from Mazatlan, Mexico

Mercury accumulation and elimination by Eurythoe complanata were evaluated through two laboratory bioassays in the absence (bioassay A) and presence (bioassay B) of sediment. Ten individuals per treatment (three replicates) were exposed to Hg in solution (0, 1.5, 1.7, 3, 7.4, 8.7, 9, and 11 microg/L) for an 8-day exposure period. At the beginning of the elimination period, the solutions (both bioassays) and sediments (bioassay B) were replaced by seawater only and clean sediment, respectively. This period lasted 8 days. The effect of Hg concentrations on Hg accumulation by worms from bioassay A was confirmed by the Kruskal-Wallis test (H = 19.43, df = 7, chi(2) = 18.475, p = 0.01), whereas this effect was nonsignificant for bioassay B. Specimens from bioassay A accumulated about double the Hg than those of bioassay B. This indicates that sediment plays an important role in the bioaccumulation process. Mercury elimination was observed only on specimens from bioassay B, where 25% to 36% of the total Hg was eliminated during 8 days. This suggests that worms need a longer period of time to completely depurate the accumulated Hg. The Hg balance was performed at the beginning and end of the experimental periods. The total Hg percentage per aquarium decreased at the end of the experiment, which suggests that a considerable amount of Hg was evaporated or adhered to the aquarium walls. This first approach points out that experimental studies using E. complanata as a test species can be useful to evaluate the potential risk produced by Hg or other toxicants on marine biota inhabiting zones subjected to anthropogenic activities.

Chronic dietary mercury exposure causes oxidative stress, brain lesions, and altered behaviour in Atlantic salmon (Salmo salar) parr

Atlantic salmon (Salmo salar L.) parr were fed for 4 months on fish meal based diets supplemented with mercuric chloride (0, 10, or 100 mg Hg kg(-1) DW) or methylmercury chloride (0, 5, or 10 mg Hg kg(-1) DW) to assess the effects of inorganic (Hg) and organic dietary mercury on brain lipid peroxidation and neurotoxicity. Lipid peroxidative products, endogenous anti oxidant enzymes, brain histopathology, and overall behaviour were measured. Methylmercury accumulated significantly in the brain of fish fed 5 or 10 mg kg(-1) by the end of the experiment, and inorganic mercury accumulated significantly in the brain only at 100 mg kg(-1) exposure levels. No mortality or growth reduction was observed in any of the exposure groups. Fish fed 5 mg kg(-1) methylmercury had a significant increase (2-fold) in the antioxidant enzyme super oxide dismutase (SOD) in the brain. At dietary levels of 10 mg kg(-1) methylmercury, a significant increase (7-fold) was observed in lipid peroxidative products (thiobarbituric acid reactive substances, TBARS) and a subsequently decrease (1.5-fold) in anti oxidant enzyme activity (SOD and glutathione peroxidase, GSH-Px). Fish fed 10 mg kg(-1) methylmercury also had pathological damage (vacoulation and necrosis), significantly reduced neural enzyme activity (5-fold reduced monoamine oxidase, MAO, activity), and reduced overall post-feeding activity behaviour. Pathological injury started in the brain stem and became more widespread in other areas of the brain at higher exposure levels. Fish fed 100 mg Hg kg(-1) inorganic mercury had significant reduced neural MAO activity and pathological changes (astrocyte proliferation) in the brain, however, neural SOD and GSH-Px enzyme activity, lipid peroxidative products (TBARS), and post feeding behaviour did not differ from controls. Compared with other organs, the brain is particular susceptible for dietary methylmercury induced lipid peroxidative stress at relative low exposure concentrations. Doses of dietary methylmercury in the range of 5 mg kg(-1) induces protective redox defences in the brain as seen from the induction of anti-oxidant enzyme SOD activity. However, above a threshold of 10 mg kg(-1) methylmercury these defences are overcome and lipid peroxidative injury (TBARS) as well as severe pathological damage and adverse behaviour become apparent.

Histopathological evidence of inorganic mercury and methyl mercury toxicity in the arctic charr (Salvelinus alpinus)

In our sustained effort to understand mechanisms of mercury toxicity in fish, the histopathological effects of a 96-h acute exposure to water-borne inorganic mercury (inorganic Hg) (15 micro gL(-1)), as well as those of a single dietary dose of inorganic and methyl mercury (methyl Hg) (0.260.05 micro g.Hgg(-1) body weight), over 30 days were examined. Samples of gills, olfactory epithelium, kidneys, and liver of arctic charr, Salvelinus alpinus, were studied using light and electron microscopy. The distribution of dietary inorganic and methyl Hg in the intestinal epithelium was determined using 203Hg microautoradiography. Gills of fish exposed to water-borne inorganic Hg presented a severe disorganization of epithelial cells after 12h and modifications of cilia of ciliated olfactory cells appeared after 24h. Nevertheless, a partial recovery was seen in both tissues by the end of the 96-h exposure period. Liver was little affected by water-borne and single-trophic-dose contamination of inorganic Hg, but dietary methyl Hg had drastic effects, despite its low dosage, with severe necrosis and alterations of cytoplasmic organization. Microautoradiograms showed that inorganic Hg was distributed evenly in the intestinal epithelium, whereas methyl Hg was found at very specific locations on the epithelial surface.

Comparative uptake, bioaccumulation, and gill damages of inorganic mercury in tropical and nordic freshwater fish

This paper reports comparative results on the bioaccumulation of inorganic mercury and resulting gill damages in the tropical fish, Trichomycterus zonatus, and a nordic species, Salvelinus alpinus, using radioisotope 203Hg techniques and scanning electron microscopy. Uptake of inorganic Hg from water was much more important in T. zonatus than in S. alpinus and the Hg concentration in S. alpinus increased at a slower rate in all tissues during the first 24 h of exposure. After 96 h, Hg concentration was 70 times higher in the kidney, 10 times higher in liver, intestine, skin, and brain, and 3 times higher in gills, muscle, and the rest of body of T. zonatus compared to S. alpinus. Gill damages in T. zonatus were more evident and occurred much earlier than for S. alpinus. According to our data, the high differences observed in the inorganic mercury uptake, bioaccumulation, and gills damages strongly suggest that T. zonatus is more sensitive to inorganic mercury pollution than S. alpinus. Further studies are urgently needed to determine whether the high sensitivity observed for T. zonatus to inorganic Hg is also present in the majority of tropical species or whether this species presents an isolated case.