Responses of Antioxidant Defense and Immune Gene Expression in Early Life Stages of Large Yellow Croaker (Pseudosciaena crocea) Under Methyl Mercury Exposure

Effect of salinity on the toxicokinetics, oxidative stress, and metallothionein gene expression in Meretrix meretrix exposed to cadmium

To understand the effect of salinity on the toxicokinetics, oxidative stress, and detoxification of cadmium-exposed Meretrix meretrix, M. meretrix were acclimatized to different salinities (8, 14, 20, 26, and 32 ppt) for 14 d, exposed to 10 μg/L Cd for 7 d, followed by a 28-day depuration period. The internal Cd concentration was determined, and the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST)), and the malondialdehyde (MDA) content were measured. The mRNA expression levels of antioxidant enzyme (Cu/Zn SOD, CAT) and detoxification-related genes metallothionein (MT) were analyzed. The mean concentrations of Cd in M. meretrix tissues were in the order gill > digestive gland > mantle > axe foot. The Cd uptake rate in the four tissues decreased with increasing salinity (range: 14-26 ppt). The Cd elimination half-lives were the highest at 8 ppt and 14 ppt salinity. Cadmium activated the four oxidative stress-related related enzymes in the gills. At the end of accumulation period, Cd exposure at 20 ppt salinity significantly increased the expression of Cu/Zn SOD. CAT expression was significantly inhibited at 20 ppt salinity, but was induced at 32 ppt. MT mRNA expression was only induced under Cd at 20 ppt salinity. At the end of depuration period, Cu/Zn SOD expression was inhibited at salinities of 8, 14, and 26 ppt. The results indicated that SOD, CAT, GST, MDA, Cu/Zn SOD, CAT, and MT were sensitive to cadmium in a water environment, and can be used as indicators of marine heavy metal pollution.

Sea anemones, methylmercury, and bacterial infection: A closer look at multiple stressors

Specimens of the Mediterranean sea anemone Anemonia viridis were exposed to methylmercury (MeHg) and bacterial infection to study their immune responses to a well-known toxic pollutant. Anemones were housed in laboratory conditions and divided into five experimental groups: 1. control (no microinjection); 2. filtered seawater + buffer injection; 3. filtered seawater + Escherichia coli injection; 4. MeHg + buffer injection; 5. MeHg + E. coli injection. Data showed an increase in antioxidant enzyme production compared to the constitutive condition, while methylmercury inhibited lysozyme production. The buffer inoculation had no statistically significant effects on the animals. In addition, electrophoretic and protease analyses revealed differences in the type of proteins produced, as well as a modulation of proteases depending on the treatment. The study demonstrated the immunomodulatory effect of the organic pollutant on A. viridis, validating its use as a model organism for marine coastal biomonitoring programmes and multiple stress studies.

Toxicity Evaluation, Oxidative, and Immune Responses of Mercury on Nile Tilapia: Modulatory Role of Dietary Nannochloropsis oculata

The current study evaluated the potential ameliorative effect of a dietary immune modulator, Nannochloropsis oculata microalga, on the mercuric chloride (HgCl2)-induced toxicity of Nile tilapia. Nile tilapia (45-50 g) were fed a control diet or exposed to ¼ LC50 of HgCl2 (0.3 mg/L) and fed on a medicated feed supplemented with N. oculata (5% and 10% (50 or 100 g/kg dry feed)) for 21 days. Growth and somatic indices, Hg2+ bioaccumulation in muscles, and serum acetylcholinesterase (AChE) activity were investigated. Antioxidant and stress-related gene expression analyses were carried out in gills and intestines. Histopathological examinations of gills and intestines were performed to monitor the traits associated with Hg2+ toxicity or refer to detoxification. Hg2+ toxicity led to significant musculature bioaccumulation, inhibited AChE activity, downregulated genes related to antioxidants and stress, and elicited histopathological changes in the gills and intestine. Supplementation with N. oculata at 10% was able to upregulate the anti-oxidative-related genes while downregulated the stress apoptotic genes in gills and intestines compared to the unexposed group. In addition, minor to no histopathological traits were detected in the gills and intestines of the N. oculata-supplemented diets. Our data showed the benefit of dietary N. oculata in suppressing Hg2+ toxicity, which might support its efficacy as therapeutic/preventive agent to overcome environmental heavy metal pollution in aquatic habitats.

Effects of mercury chloride on antioxidant and inflammatory cytokines in zebrafish embryos

In this study, a zebrafish embryo toxicity model was employed, utilizing 24 h postfertilization (hpf) zebrafish embryos. These embryos were treated with varying concentrations of mercuric chloride for 96 h under static conditions. We assessed multiple parameters that reflected developmental abnormalities, behavioral alterations, morphological anomalies, antioxidant enzyme activities, including those of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione S-transferase (GST), immune messenger RNA transcription levels of key factors such as tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclooxygenase 2 (COX-2), as well as protein expression of TNF-α. The results revealed that embryos exposed to higher concentrations of mercury exhibited reduced hatchability and increased rates of morphological abnormalities and mortality at 48, 72, and 96 hpf. In addition, a concentration-dependent increase in developmental abnormalities, including cardiac edema, reduced body length, yolk sac edema, scoliosis, and bent tails, was observed. Larval behaviors, such as touch-induced escape responses, startle reactions, and turning actions, were found to be diminished in a concentration-dependent manner. Additionally, the activities of various antioxidative enzymes, such as SOD, CAT, and GST, exhibited an increase at higher mercury concentrations, with the exception of GPX activity, which decreased significantly in a dose-dependent manner (p < 0.05). Pro-inflammatory cytokine transcription levels, specifically TNF-α, IL-1β, IL-6, and COX-2, were significantly upregulated in a dose-dependent manner in the mercuric (II) chloride (HgCl2 ) treatment group compared with the control group. TNF-α protein expression was notably elevated in the larvae group treated with 300 and 400 nM HgCl2 .

Effects of heavy metals on fish physiology - A review

The pollution by heavy metals poses a serious threat to the aquatic environment and to the organisms if the concentration of heavy metals in the environment exceeds the safe limits. Due to their non-biodegradable and long persistence nature in the environment, heavy metals cause toxicity in fish by producing oxygen reactive species through oxidizing radical production. In this review, we investigated the effects of heavy metals on fish physiology with special emphasis on hemato-biochemical properties, immunological parameters especially hormones and enzymes, histopathology of different major organs and underlying molecular mechanisms. All those parameters are significantly affected by heavy metal exposure and are found to be important bio-monitoring tools to assess heavy metal toxicity. Hematological and biochemical alterations have been documented including cellular and nuclear abnormalities in different fish species exposed to different concentrations of heavy metals. Major fish organs (gills, liver, kidneys) including intestine, muscles showed different types of pathology specific to organs in acute and chronic exposure to different heavy metals. This study also revealed the expression of different genes involved in oxidative stress and detoxification of heavy metals. In a nutshell, this article shades light on the manipulation of fish physiology by the heavy metals and sought attention in the prevention and maintenance of aquatic environments particularly from heavy metals contaminations.

Chronic Toxic Effects of Waterborne Mercury on Silver Carp (Hypophthalmichthys molitrix) Larvae

Mercury (Hg) is a kind of heavy metal pollutant widely existing in the aquatic environment, and it is also recognized to have a highly toxic effect on fish. In this study, silver carp (Hypophthalmichthys molitrix) larvae were exposed to 0 (control), 1, 5, and 10 μg/L Hg2+ for 2 weeks. Antioxidant ability, neurotoxicity, and thyroid hormones (THs) content were evaluated. In comparison with the control, the superoxide dismutase (SOD) activity and the glutathione (GSH) activity were lower in silver carp exposed to 10 μg/L Hg2+. The lowest catalase (CAT) activity was found in the 10 μg/L Hg2+, while malondialdehyde (MDA) content was not significantly different among all groups. Compared with the control, monoamine oxidase (MAO) activity and nitric oxide (NO) content were significantly higher in the 10 μg/L Hg2+, while acetylcholinesterase (AChE) activity significantly decreased. Compared with the control, triiodothyronine (T3) content was significantly higher in the 1 μg/L Hg2+ and significantly lower in the 10 μg/L Hg2+; the 1 μg/L and 5 μg/L Hg2+ groups had significantly higher thyroxine (T4) content than the other groups. In the 1 μg/L Hg2+, the integrated biomarker response (IBR) index value was the highest. In summary, exposure to Hg could decrease the antioxidant ability, cause changes in neurotoxic parameters, and induce disorders of the thyroid hormone system in silver carp larvae. The results of this study may contribute to the understanding of the adverse effects of chronic mercury poisoning on fish.

Effect of Methylmercury Exposure on Bioaccumulation and Nonspecific Immune Respsonses in Hybrid Grouper Epinephelus fuscoguttatus × Epinephelus lanceolatus

Simple Summary

The head kidney was primary organ that accumulated methylmercury in hybrid grouper. Muscle tissue had lower methylmercury content than the head kidney and liver. Nonspecific immune responses and bioaccumulation of methylmercury were linked to hybrid grouper health.

Abstract

Mercury (Hg) is a dangerous heavy metal that can accumulate in fish and is harmful when consumed by humans. This study investigated the bioaccumulation of mercury in the form of methylmercury (MeHg) and evaluated nonspecific immune responses such as phagocytic activity and superoxide anion (O₂⁻) production in hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus). The hybrid grouper leukocytes were incubated with methylmercury chloride (CH₃HgCl) at concentrations of 10–10,000 µg/L to determine cell viability, phagocytic activity, and O₂⁻ production in vitro. Subsequently, the grouper were exposed daily to CH₃HgCl mixed in the experimental diets at concentrations of 0, 1, 5, and 10 mg/kg for 28 days. The bioaccumulation of MeHg in the liver, head kidney, and muscle tissue was measured, and the phagocytic activity and O₂⁻ production were evaluated. In vitro results indicated that cell viability was significantly lower than that of the control group at concentrations > 500 µg/L. The phagocytic rate and O₂⁻ production at concentrations ˃ 500 and ˃ 200 µg/L, respectively, were significantly lower than those of the control group. The dietary exposure demonstrated that MeHg accumulated more substantially in the liver and head kidney compared with the muscle tissue in the treatment groups. Moreover, the cumulative concentration significantly increased with higher concentrations and more days of exposure. The phagocytic rate and O₂⁻ production in the treatment groups were significantly lower than those in the control group from days 2 and 1, respectively. In conclusion, hybrid grouper accumulated significant MeHg in the liver and head kidney compared with the muscle tissue, and higher concentrations and more exposure days resulted in decreased cell viability, phagocytic activity, and O₂⁻ production.

Nannochloropsis oculata feed additive alleviates mercuric chloride-induced toxicity in Nile tilapia (Oreochromis niloticus)

Using microalgae to alleviate the adverse effects of aquaculture pollutants, including metals, has recently gained much attention. In this context, bioaccumulation, hematological indices, oxidative and antioxidant responses, and histopathological alterations were investigated in Nile tilapia (Oreochromis niloticus) fed with either a control diet or diets containing Nannochloropsis oculata (N. oculata) after exposure to mercuric chloride in order to evaluate the role of this microalgae in protecting against mercury-induced toxicity. Fish exposed to HgCl2 at a dose of ¼ LC50 (0.3 mg/L) (Hg group) for 7-21 days exhibited a significant increase in total mercury concentration with a bioaccumulation pattern of liver>gills>muscle, and a significant decrease in all blood indices except mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), monocyte counts, and neutrophil counts. Malondialdehyde (MDA) levels were significantly increased in the Hg group at all time points relative to the control. Glutathione peroxidase (GPx) activity was significantly increased at days 14 and 21, while catalase (CAT) and GPx activities increased and decreased, respectively, at day 7 compared to the control. Additionally, lysozyme activity and immunoglobulin M (IgM) were significantly decreased in the Hg-exposed group. Severe histopathological alterations were evident in the liver, kidneys, and gills. However, supplementation with N. oculata at a low (5%, 50 g/kg feed) or high (10%, 100 g/kg feed) dose stabilized all parameters and reduced the severity of the histopathological alterations with the high N. oculata diet showing more prominent effects. These results suggest that feeding N. oculata protects Nile tilapia against mercuric chloride-induced toxicity.

Modulation of physiological oxidative stress and antioxidant status by abiotic factors especially salinity in aquatic organisms

Exposure to a variety of environmental factors such as temperature, pH, oxygen and salinity may influence the oxidative status in aquatic organisms. The present review article focuses on the modulation of oxidative stress with reference to the generation of reactive oxygen species (ROS) in aquatic animals from different phyla. The focus of the review article is to explore the plausible mechanisms of physiological changes occurring in aquatic animals due to altered salinity in terms of oxidative stress. Apart from the seasonal variations in salinity, global warming and anthropogenic activities have also been found to influence oxidative health status of aquatic organisms. These effects are discussed with an objective to develop precautionary measures to protect the diversity of aquatic species with sustainable conservation. Comparative analyses among different aquatic species suggest that salinity alone or in combination with other abiotic factors are intricately associated with modulation in oxidative stress in a species-specific manner in aquatic animals. Osmoregulation under salinity stress in relation to energy demand and supply are also discussed. The literature survey of >50 years (1960-2020) indicates that oxidative stress status and comparative analysis of redox modulation have evolved from the analysis of various biotic and/or abiotic factors to the study of cellular signalling pathways in these aquatic organisms.

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 comparative study of effects of dietary mercuric chloride and methylmercury chloride on growth performance, tissue accumulation, stress and immune responses, and plasma measurements in Korean rockfish, Sebastes schlegeli

Mercury (Hg) is known as a highly toxic heavy metal, and its toxicity varies depending on its form due to different toxicokinetics between inorganic and organic Hg. Limited information on comparison of Hg toxicity concerning its chemical form by oral exposure is currently available in cultured fishes. Therefore, we conducted a comparative study to have a better understanding of distinct toxic effects between mercuric chloride (HgCl₂) and methylmercury chloride (CH₃HgCl) in Korean rockfish. The 12-weeks dietary exposure of HgCl₂ and CH₃HgCl with its graded levels (0.4-6.4 ppm) (2 × 5 factorial design) in the young-of-the-year rockfish (initial weight: 82 ± 0.3 g) resulted in neither interactive nor main effects on whole-organism responses, including growth, feed utilization, and survival. However, the distinct pattern of Hg accumulation between the two forms in dorsal muscle, brain, liver and kidney tissues was observed, showing that the rockfish fed the CH₃HgCl-contained diets exhibited the dose-dependent accumulation throughout the sampling points (1, 2, 4, 8, and 12 weeks post feeding), whereas those fed the HgCl₂-contained diets did not show such response. The CH₃HgCl exposure induced higher oxidative stress and immunotoxicity, reflected by the elevated plasma superoxide dismutase and lysozyme activities, respectively. In addition, the CH₃HgCl-induced alteration in plasma measurements, including the plasma aspartate transaminase activity and total protein level was found. Taken together, the dietary exposure of methylmercury chloride had more pronounced toxic effects than mercuric chloride in the young-of-year rockfish, needed to be taken into consideration for regulation of maximum allowed levels for Hg by its chemical form.

Short-term exposure to norfloxacin induces oxidative stress, neurotoxicity and microbiota alteration in juvenile large yellow croaker Pseudosciaena crocea

In recent years, antibiotics have been widely detected in coastal waters of China, which raising concerns for coastal biodiversity and aquaculture. This study evaluated the effects of short-term exposure of norfloxacin (NOR) on oxidative stress and intestinal health of the large yellow croaker Pseudosciaena crocea. Juvenile fish were exposed to four concentrations of NOR (0.1, 10, 100 and 1000 μg/L) for 14 days. The results showed that NOR inhibited growth and threatened the survival of juveniles. According to the changes of intestinal microbiota, we found that NOR led to a significant decrease in intestinal microbiota diversity, with the decreased relative abundance of Proteobacteria, but the increased Tenericutes. From the perspective of microbial function, NOR inhibited metabolism, cellular defence mechanism and information transduction process. In terms of biochemical indicators, NOR caused an increase in malondialdehyde (MDA) level and inhibited superoxide dismutase (SOD) and acetyl cholinesterase (AChE) activities. Catalase (CAT) activity was activated at low concentration but significantly inhibited at high concentration of NOR. Moreover, there was a high correlation between change in biochemical indicators and change in the microbial community. Overall, environmentally relevant concentrations (0.1 μg/L) and high concentrations (10, 100 and 1000 μg/L) of NOR have negative effects on the defence function and intestinal health of large yellow croaker juveniles.

Tissue-Specific Accumulation and Antioxidant Defenses in Flounder (Paralichthys olivaceus) Juveniles Experimentally Exposed to Methylmercury

Methylmercury (MeHg) is the most toxic form of mercury and can accumulate in the cells of marine organisms, such as fish, causing adverse effects on various physiological functions. This study examined MeHg accumulation and its toxicological role in antioxidant defenses in tissues, including the liver, gills, and muscle of flounder (Paralichthys olivaceus) juveniles. After 30 d of MeHg exposure (0, 0.1, 1.0, 10.0, and 20.0 µg L^-1), the accumulation of MeHg in the three tissues correlated positively with the concentration of MeHg and exhibited tissue specificity in the order of liver > gills > muscle. Among the antioxidant markers, the activities of SOD (superoxide dismutase) and GST (glutathione S-transferase) as well as the content of glutathione (GSH) in the liver and gills were induced at 0.1-10.0 µg L^-1 but repressed at 20.0 µg L^-1. The activities of SOD and GST and the content of GSH in the muscle significantly increased with increasing MeHg concentration. Catalase (CAT) activity in the liver was induced at 0.1-1.0 µg L^-1 but inhibited at 10.0-20.0 µg L^-1, whereas exposure to MeHg did not remarkably affect CAT activity in the gills and muscle. The levels of lipid peroxidation (LPO) increased dose dependently, showing tissue specificity with the highest level in the liver, then the gills, followed by muscles. Overall, higher sensitivity to oxidative stress induced by MeHg was detected in the liver than the gills and muscle. These findings improve our understanding of the tissue-specific accumulation of heavy metals and their roles in antioxidant responses in marine fish subjected to MeHg exposure.

Thermal stress accelerates mercury chloride toxicity in Oreochromis niloticus via up-regulation of mercury bioaccumulation and HSP70 mRNA expression

Mercury (Hg) is an environmental pollutant that threatens aquatic life. Many environmental factors, including water temperature, are reported to influence the toxicity of dissolved chemicals in the aquatic ecosystem. Therefore, we investigated the impact of thermal stress on Hg-induced subchronic toxicity in Nile tilapia (Oreochromis niloticus). Fish were randomly allocated into five groups. Group I served as the control and kept at 25 °C. Groups II, III, IV, and V were reared at 25, 28, 31, and 34 °C, respectively, and co-exposed to HgCl₂ (1/10 LC₅₀) for 42 days. Blood and tissue samples were collected after 21 and 42 days. All HgCl₂-exposed groups exhibited significant elevations in serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, and creatinine, along with decreases in the serum total protein and albumin. In addition, marked reductions in antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSPx), were observed. Remarkable increases in Hg tissue concentrations were detected along with increases in heat shock protein (HSP) 70 mRNA expression. Interestingly, the patterns data that were recorded were more coincident with the water temperature than the period of exposure. In conclusion, water temperature and exposure period are two crucial factors modulating HgCl₂-induced toxicity and bioaccumulation in Nile tilapia. Our findings provide new insights concerning the impact of thermal stress as an environmental factor on Hg toxicity and bioaccumulation in Nile tilapia and, in turn, on fish and fish consumer health.

Antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae under methylmercury exposure

Methylmercury (MeHg) is a highly toxic contaminant in coastal environments and poses threats to marine fish in early life stages (ELSs). However, MeHg toxicity to fish embryos and larvae is not well investigated. This study investigated the antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae exposed to waterborne MeHg (0, 0.1, 1.0 and 10.0 μg L^-1) for 35 days, from embryogenesis to settlement. The results revealed that metal accumulation in the larvae was positively correlated with MeHg concentration, reduced larval growth and survival. The activities of catalase and glutathione reductase were significantly increased at 10.0 μg L^-1, while glutathione peroxidase activity and lipid peroxidation level were significantly increased at concentrations over 1.0 μg L^-1. The corresponding antioxidant-related genes were upregulated under MeHg exposure (cat and gpx at 10.0 μg L^-1; gr over 1.0 μg L^-1). Lysozyme content was significantly increased, but immunoglobulin M content was significantly decreased at 10.0 μg L^-1. The immune-related genes were significantly upregulated (hsp70 at 0.1 and 10.0 μg L^-1; lzm and il-1β over 1.0 μg L^-1; tnf-α and il-6 at 10.0 μg L^-1) or downregulated (igm, over 0.1 μg L^-1). Overall, MeHg exposure induced oxidative stress and caused immunotoxicity at concentrations over 1.0 μg L^-1 and 10.0 μg L^-1, respectively. The transcription of selected genes correlated with the corresponding biochemical markers in response to MeHg toxicity. These findings improve our knowledge to better understand the mechanisms by which marine fish at ELSs cope with oxidative stress and immunotoxicity induced by MeHg.

Diphenyl diselenide dietary supplementation protects against methylmercury-chloride-induced immunotoxicity in the head kidney and spleen of grass carp (Ctenopharyngodon idella) via regulation of purinergic signaling and the NLRP3 inflammasome

This study aimed to evaluate whether dietary supplementation with diphenyl diselenide (Ph₂Se₂) would prevent the impaired immune and inflammatory responses elicited by methylmercury chloride (CH₃HgCl) via protective effects on purinergic signaling in fish immune organs. Tissue and lymphocytic nucleoside triphosphate diphosphohydrolase (NTPDase) activity for adenosine triphosphate (ATP) and adenosine diphosphate (ADP) was downregulated in the head kidney and spleen of grass carp (Ctenopharyngodon idella) exposed to CH₃HgCl. Concomitantly, adenosine deaminase (ADA) activity was upregulated. Further, nucleotide-binding oligomerization domain-like receptor (NLRP3) inflammasome gene expression was upregulated in the spleen and head kidney of CH₃HgCl-exposed grass carp. Dietary supplementation with Ph₂Se₂ ameliorated these CH₃HgCl-mediated alterations on purinergic enzymes, and their activities returned to baseline levels (except NTPDase activity for ADP). Based on these results, purinergic signaling in immune organs and lymphocytes can be considered a pathway linked to pro-inflammatory effects during exposure to environmental CH₃HgCl concentrations, which may contribute to mortality of the affected fish. Since dietary supplementation with 3 mg Ph₂Se₂/kg in the feed prevented the CH₃HgCl-induced alterations, it can be considered a potential suitable treatment to prevent impaired immune and inflammatory responses caused by Hg.

Dietary Aroclor 1254-Induced Toxicity on Antioxidant Capacity, Immunity and Energy Metabolism in Chinese Mitten Crab Eriocheir sinensis: Amelioration by Vitamin A

Effects of dietary Polychlorinated biphenyl (PCB) exposure and dietary vitamin A supplementation on Chinese mitten crab Eriocheir sinensis were studied with the aim to explain dietary PCB toxicity and toxic alleviation by vitamin A intake in crab. Four diets were used including three experimental diets containing 0, 80000 or 240000 IU/kg vitamin A with each experimental diet containing 10 mg PCB/kg diet, and a control diet (without vitamin A and PCB supplementation) in 56 days feeding trial. Crabs fed the PCB-only diet had significantly lower weight gain than those fed the control diet. No significant difference was observed in crab survival among all groups. Crabs fed the PCB-only diet had a significantly higher malondialdehyde content and antioxidase superoxide dismutase activity in the serum and hepatopancreas, and higher erythromycin N-demethylase and glutathione S-transferase activities in the hepatopancreas than those fed the control diet. However, supplementation of dietary vitamin A decreased the levels of all these parameters. The hepatopancreatic cytochrome P450 2 and 4 (CYP2, CYP4), fatty acid binding proteins 3 and 10 (FABP3, FABP10) and intracellular lipolytic enzyme (IL) Messenger Ribonucleic Acid (mRNA) levels in the PCB-only group were significantly higher than those in the control group, and dietary 240000 IU/kg vitamin A supplementation decreased hepatopancreatic CYP4, FABP3, FABP10 and IL enzyme mRNA level. The crabs fed 80000 IU/kg vitamin A supplementation diet had the highest level of retinoid X receptor mRNA in the hepatopancreas. The structure of the hepatopancreas was damaged and the deposit of lipid droplets decreased with dietary PCB exposure. Both levels of vitamin A supplementation alleviated the damage and increased lipid droplets in the hepatopancreas. Dietary PCB exposure significantly reduced total hemocyte count (THC), and phenoloxidase, acid phosphatase activities in the serum. Post-challenge survival of crab in the experimental PCB-only diet group was low compared with that in the control. Supplementation of 240000 IU/kg vitamin A significantly increased the THC and phenoloxidase activity in the serum and post-challenge survival compared with those in the PCB-only group. This study indicates that dietary vitamin A can improve the antioxidant capacity, immune response, detoxification enzymes activities, energy metabolism and hepatopancreas tissue structure of Chinese mitten crab fed PCB contaminated diets.

The Toxicological Effects of Mercury Exposure in Marine Fish

Since the Minamata incident in Japan, the public have become increasingly aware of the negative health effects caused by mercury pollution in the ocean. Consequently, there has been significant interest in the health of humans eating fish exposed to mercury (Hg). However, the toxicity of mercury to the marine fish themselves has received far less attention. In this review, we summarize mercury accumulation in marine fish and the toxicological effects of mercury exposure. Results showed that the bioaccumulation of mercury in marine fish was highly variable, and its concentration was affected by the specific physiological and ecological characteristics of different fish species. Mercury exposure can produce teratogenic, neurotoxic effects, and reproductive toxicity. These effects can then cause harm to cells, tissues, proteins and genes, and ultimately, the survival, growth, and behavior of marine fish. Future studies should afford more attention to the toxicological effect of mercury exposure upon marine fish.