Tissue-specific accumulation of cadmium and its effects on antioxidative responses in Japanese flounder juveniles

Novel mechanistic insights into Cr(VI) and Cr(III) induced discrepancies of cellular toxicity and oxidative injury events in Eisenia fetida

Chromium (Cr) poses a high ecological risk, however the toxic mechanisms of Cr in different valence states to soil organisms at cellular and molecular levels are not exactly. In this study, the Eisenia fetida coelomocytes and Cu/Zn-superoxide dismutase (Cu/Zn-SOD) were chosen as the target subjects to investigate the effects and mechanisms of cellular toxicity induced by Cr(VI) and Cr(III). Results indicated that Cr(VI) and Cr(III) significantly reduced the coelomocytes viability. The level of reactive oxygen species (ROS) was markedly increased after Cr(VI) exposure, which finally reduced antioxidant defense abilities, and induced lipid peroxidation and cellular membrane damage in earthworm coelomocytes. However, Cr(III) induced lower levels of oxidative stress and cellular damage with respect to Cr(VI). From a molecular perspective, the binding of both Cr(VI) and Cr(III) with Cu/Zn-SOD resulted in protein backbone loosening and reduced β-Sheet content. The Cu/Zn-SOD showed fluorescence enhancement with Cr(III), whereas Cr(VI) had no obvious effect. The activity of Cu/Zn-SOD continued to decrease with the exposure of Cr. Molecular docking indicated that Cr(III) interacted more readily with the active center of Cu/Zn-SOD. Our results illustrate that oxidative stress induced by Cr(VI) and Cr(III) plays an important role in the cytotoxic differences of Eisenia fetida coelomocytes and the binding of Cr with Cu/Zn-SOD can also affect the normal structures and functions of antioxidant defense-associated protein.

Acute waterborne cadmium exposure induces liver ferroptosis in Channa argus

The impact of cadmium (Cd) toxicity on fish liver injury has received much attention in recent years. Currently, autophagy, apoptosis and endoplasmic reticulum stress were reported in Cd exposed fish liver, and if there are other mechanisms (such as ferroptosis) and relevant signaling pathways involved in fish remains unknown. An experiment was conducted to investigate Cd toxicity in Channa argus (Cantor, 1842) exposed to 0, 1.0, and 2.0 mg Cd/L of water for 96 h. Cd disrupted the structure of mitochondria in the liver. Besides, Cd induced ferroptosis by significantly increasing the level of Fe2+, ROS, MDA and significantly decreasing the level of Ferritin, GSH, GSH-Px, GPX4, GST and SOD (p < 0.05 in all cases). In addition, the mRNA expression of ferroptosis related genes, gpx4 and slc7a11, were significantly downregulated by Cd. Moreover, Cd exposure significantly inhibited the Nrf2/Keap1 signaling pathway, one of the pathways involved in ferroptosis, by upregulating the mRNA levels of keap1a and keap1b, and downregulating the mRNA levels of nrf2 and its target genes (ho-1, nqo1 and cat). Cd exposure also caused extensive accumulation of vacuoles and lipid droplets in liver, as well as an increase in triglyceride content. Cd significantly affected lipid metabolism related enzyme activity and gene expression, which were also regulated by Nrf2/Keap1 signaling pathway. In summary, these results indicate that ferroptosis is a mechanism in waterborne Cd exposed fish liver injury via the Nrf2/Keap1 signaling pathway and the Cd induced hepatic steatosis is also modulated by Nrf2/Keap1 pathway at the whole-body level in fish. These findings provide new insights into the fish liver injury and molecular basis of Cd toxicity.

Differential eco-toxicological responses toward Eisenia fetida exposed to soil contaminated with naphthalene and typical metabolites

Naphthalene (NAP) was frequently detected in polycyclic aromatic hydrocarbons (PAHs)-contaminated soil, and its residues may pose an eco-toxicological threat to soil organisms. The toxic effects of NAP were closely tied to phenolic and quinone metabolites in biological metabolism. However, the present knowledge concerning the eco-toxicological impacts of NAP metabolites at the animal level is scanty. Here, we assessed the differences in the eco-toxicological responses of Eisenia fetida (E. fetida) in NAP, 1-naphthol (1-NAO) or 1,4-naphthoquinone (1,4-NQ) contaminated soils. NAP, 1-NAO, and 1,4-NQ exposure triggered the onset of oxidative stress as evidenced by the destruction of the antioxidant enzyme system. The lipid peroxidation and DNA oxidative damage levels induced by 1-NAO and 1,4-NQ were higher than those of NAP. The elevation of DNA damage varied considerably depending on differences in oxidative stress and the direct mode of action of NAP or its metabolites with DNA. All three toxicants induced different degrees of physiological damage to the body wall, but only 1, 4-NQ caused the shedding of intestinal epithelial cells. The integrated biomarker response for different exposure times illustrated that the comprehensive toxicity at the animal level was 1,4-NQ > 1-NAO > NAP, and the time-dependent trends of oxidative stress responses induced by the three toxicants were similar. At the initial stage, the antioxidant system of E. fetida responded positively to the provocation, but the ability of E. fetida to resist stimulation decreased with the prolongation of time resulting in provocation oxidative damage. This study would provide new insights into the toxicological effects and biohazard of PAHs on soil animals.

Lead and cadmium in blood and tissues of Atlantic bluefin tuna (Thunnus thynnus L., 1758)

Cadmium (Cd) and lead (Pb) levels in blood and tissues of Atlantic bluefin tuna were analysed to gather information regarding their distribution, accumulation and inter-relationships, as well as to examine how sex affects them. In the whole population, the concentration range was from below the detection limit (bone) to 8.512 μg g-1 (liver) for Cd, and from below detection limit (bone and gills) to 0.063 μg g-1 (kidney) for Pb. The median concentration in the muscles (0.008 and 0.029 μg g-1 for Cd and Pb, respectively) was 10 times less than the maximum permitted for consumption. Sex was shown to be an important variable affecting concentrations of Cd in both liver and kidneys, so taking into account sex when interpreting results is highly recommended. The importance of Cd and Pb bioaccumulation in fishery by-products, increasingly important in commercial circuits, is also highlighted.

Environmental relevant concentrations of polystyrene nanoplastics and lead co-exposure triggered cellular cytotoxicity responses and underlying mechanisms in Eisenia fetida

Heavy metal pollution of soils and the widespread use of plastics have caused environmental problems worldwide. Nanoplastics (NPs) contaminants in water and soil environments can adsorb heavy metals, thereby affecting the bioavailability and toxicity of heavy metals. In this paper, the effect of co-exposure of polystyrene microspheres with 100 nm particle size and lead acetate (Pb) on the Eisenia fetida coelomocytes was investigated. The environmental concentration of NPs used was 0.01 mg/L and the concentration of Pb ranged from 0.01 to 1 mg/L, and the exposed cells were incubated at 298 k for 24 h. Our study demonstrated that exposure of cells to environmental relevant concentrations of NPs did not significantly affect the cytotoxicity of Pb exposure. It was shown that co-exposure induced cellular production of reactive oxygen species (ROS, increased to 134.4 %) disrupted the antioxidant system of earthworm body cavity cells, activated superoxide dismutase and catalase (CAT), produced reduced glutathione, and inhibited glutathione-dependent enzyme (GST) activity (Reduced to 64 %). Total antioxidant capacity (T-AOC) is first enhanced against ROS due to the stress of NPs and Pb. When the antioxidant reserves of cells are exhausted, the antioxidant capacity will decrease. The level of malondialdehyde, a biomarker of eventual lipid peroxidation, increased to 231.7 %. At the molecular level, due to co-exposure to NPs and Pb, CAT was loosely structured and the secondary structure is misfolded, which was responsible for exacerbating oxidative damage in E. fetida coelomocytes. The findings of this study have significant implications for the toxicological interaction and future risk assessment of co-contamination of NPs and Pb in the environment.

The Role of Glutathione and Sulfhydryl Groups in Cadmium Uptake by Cultures of the Rainbow Trout RTG-2 Cell Line

The aim of this study is to investigate the role of cellular sulfhydryl and glutathione (GSH) status in cellular cadmium (Cd) accumulation using cultures of the rainbow trout cell line RTG-2. In a first set of experiments, the time course of Cd accumulation in RTG-2 cells exposed to a non-cytotoxic CdCl2 concentration (25 μM) was determined, as were the associated changes in the cellular sulfhydryl status. The cellular levels of total GSH, oxidized glutathione (GSSG), and cysteine were determined with fluorometric high-performance liquid chromatography (HPLC), and the intracellular Cd concentrations were determined with inductively coupled plasma mass spectrometry (ICP-MS). The Cd uptake during the first 24 h of exposure was linear before it approached a plateau at 48 h. The metal accumulation did not cause an alteration in cellular GSH, GSSG, or cysteine levels. In a second set of experiments, we examined whether the cellular sulfhydryl status modulates Cd accumulation. To this end, the following approaches were used: (a) untreated RTG-2 cells as controls, and (b) RTG-2 cells that were either depleted of GSH through pre-exposure to 1 mM L-buthionine-SR-sulfoximine (BSO), an inhibitor of glutathione synthesis, or the cellular sulfhydryl groups were blocked through treatment with 2.5 μM N-ethylmaleimide (NEM). Compared to the control cells, the cells depleted of intracellular GSH showed a 25% reduction in Cd accumulation. Likewise, the Cd accumulation was reduced by 25% in the RTG-2 cells with blocked sulfhydryl groups. However, the 25% decrease in cellular Cd accumulation in the sulfhydryl-manipulated cells was statistically not significantly different from the Cd accumulation in the control cells. The findings of this study suggest that the intracellular sulfhydryl and GSH status, in contrast to their importance for Cd toxicodynamics, is of limited importance for the toxicokinetics of Cd in fish cells.

Toxic and bioaccumulative effects of zinc nanoparticle exposure to goldfish, Carassius auratus (Linnaeus, 1758)

The widespread use of produced metal oxide nanoparticles (NPs) has increased major concerns about their impact on human as well as aquatic animal health. The present study shows that exposure to different concentrations of zinc oxide (ZnO) NPs led to high accumulations of Zn ions in the metabolic organs of fish (liver and gills), resulting in severe oxidative stress in Carassius auratus. The goldfish (C. auratus) was chosen as an aquatic species for the evaluation of the potential toxicity of aqueous ZnO-NPs (Treatments of hemoglobin and neutrophils (0, 0.5, 1, and 1.5 mg L- 1) following 14 days of exposure. A range of histological and hematological factors were examined. Exposure to the NPs produced significant reduction of red blood cell and white blood cell counts, hematocrit) were found to produce no significant differences in lymphocyte, monocyte, and eosinophil counts; as well as the mean corpuscular hemoglobin concentrations index (P > 0.05). Moreover, the results revealed significant alterations in serum biochemical parameters, hepatic enzyme levels, and immune and antioxidant responses; except for total protein and superoxide dismutase (SOD) of C. auratus exposed to ZnO-NPs, particularly at the 1 and 1.5 mg L- 1 concentrations. Fish exposed to 1 and 1.5 mg L-1 ZnO-NPs displayed a significant reduction in alternative complement pathway activity, lysozyme, and total protein contents of mucus compared to those in the control group. The results showed that hepatic SOD and catalase, and gill catalase activity were significantly decreased, and their malondialdehyde levels increased at 1 and 1.5 mg L-1 ZnO-NPs compared to the control group (P < 0.05). Significant accumulations of ZnO-NPs were observed in the liver, kidney, and gill tissues of fish leading to severe histopathological alterations in these organs. These results suggest that water-borne ZnO-NPs can easily accumulate in metabolic organs and lead to oxidative stress and destructive effects on the physiological features of C. auratus.

Immunomodulation, Fish Health and Resistance to Staphylococcus aureus of Nile Tilapia (Oreochromis niloticus) Fed Diet Supplemented with Zinc Oxide Nanoparticles and Zinc Acetate

Recently some metal-based nanoparticles have gained serious attention from aquaculture and the fish feed industry as feed supplements. Oral supplementation of zinc oxide nanoparticles (ZnO-NPs) in fish feed, replacing Zn acetate (conventionally used zinc), is suggested as a cost-effective and efficient approach. Our study assessed the response of Nile tilapia, Oreochromis niloticus, fingerlings after its diet supplemented with chemically synthesized ZnO-NPs and zinc acetate under controlled conditions. ZnO-NPs were chemically synthesized and characterized. Tilapia fingerlings with an average body weight of 09.12 ± 1.23 g were randomly distributed into five groups. An 8-week trial was set with control and four experimental groups. Basal diet (D1) was used as control, whereas D2, D3 and D4 comprising 20, 40, and 60 mgkg-1 ZnO-NPs supplementation were experimental diets. Additionally, D5 was composed of a basal diet supplemented with 40 mgkg-1 of conventionally used zinc acetate. Significant improvement (P < 0.05) was found in nanoparticles and Zn acetate supplemented groups as compared to control, while the 40 mgkg-1 Zn-NPs supplemented diet (D3) showed best performance in terms of health parameters, oxidative status and disease resistance. Antioxidant profiling was based on catalase, superoxide dismutase, glutathione's transferase, and malondialdehyde; hematology included Hb, WBCs, RBCs, HCT MCV, MCH and MCHC; immunological parameters comprised IgM, lysozyme activity, phagocytic activity, respiratory burst activity, cholesterol, aspartate aminotransferase, alanine aminotransferase, glucose content, and total serum proteins. We report that the D3 (40 mgkg-1 ZnO-NPs supplementation) significantly (P < 0.05) improved health-related parameters as compared to the other groups. Moreover, D3 also showed significantly decreased mortality percentage when challenged by Staphylococcus aureus, while the Zn acetate supplemented diet group showed better results as compared to control. Overall results suggest the basal diet supplemented with 40 mgkg-1 ZnO-NP for enhanced health parameters, oxidative status, immune response, and disease resistance. Hence, 40mgkg-1 ZnO-NP can be recommended to formulate the practical diet of fish to boost health improvement, immunomodulation, and resistance to bacterial disease.

Single and joint toxic effects of waterborne exposure to copper and cadmium on Coregonus ussuriensis Berg

Heavy metal contamination severely affects the aquatic environment and organisms. Copper (Cu) and cadmium (Cd) are two of the most common heavy metal contaminants that impair the survival, development, and reproduction of aquatic organisms. With the growth of agriculture and industry, there is a possibility of heavy metal pollution in Coregonus ussuriensis Berg's water source. However, there are no published studies on the toxicity to C. ussuriensis. Acute toxicity experiments in C. ussuriensis revealed the 96-h median lethal concentrations of copper and cadmium to be 0.492 mg·L-1 (95% confidence interval: 0.452-0.529) and 1.548 mg·L-1 (95% confidence interval: 1.434-1.657), respectively, and safe concentrations of 4.92 µg·L-1 and 15.48 µg·L-1, respectively. C. ussuriensis was then treated for 96 h with Cu (20% of 96 h LC50), Cd (20% of 96 h LC50), and a combination of Cu and Cd (20% of Cu 96 h LC50 + 20% of Cd 96 h LC50). The histological damage caused by the three different exposure modes to the liver and gills of C. ussuriensis was verified using hematoxylin and eosin staining. All three exposure modes caused different degrees of vacuolization, nuclear consolidation, and necrosis in the liver tissue of C. ussuriensis and edema, hyperplasia, laminar fusion, and epithelial elevation in the gill tissue compared with the reference group. The severity of the damage increased with increasing exposure time. Anti-oxidant activity in the gill and liver tissues were measured using enzyme activity assay kits to reflect oxidative stress induced by copper and cadmium exposure alone and in combination. The enzyme activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH) were substantially higher than those in the reference groups. However, the activities of the enzymes decreased with increasing exposure time. Malondialdehyde (MDA) activity significantly increased during exposure in relation to that in the reference group. Analysis of immune gene expression in C. ussuriensis gill and liver tissues was executed using real-time inverse transcript polymerase chain response (RT-PCR). The expression levels of the pro-inflammatory cytokines interleukin one beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) were positively correlated with exposure time and were significantly upregulated with increasing exposure time. Metallothionein (MT) gene expression levels were significantly upregulated in the short term after exposure compared to the reference group but decreased with increasing exposure time. Our results indicate that exposure to aqueous copper and cadmium solutions, either alone or in combination, causes histopathological damage, oxidative stress, and immunotoxicity in C. ussuriensis gill and liver tissue. This study investigated the toxic effects of copper and cadmium on C. ussuriensis to facilitate the monitoring of heavy metals in water sources for healthy aquaculture.

Contaminant-induced oxidative stress underlies biochemical, molecular and fatty acid profile changes, in gilthead seabream (Sparus aurata L.)

Chemical contaminants such as heavy metals, polybrominated diphenyl ethers (PBDEs) and drugs, are constantly found in the marine environment determining the interest of the scientific community for their side effects on animal welfare, food safety and security. Few studies have analyzed the effects of mix of contaminants in fish, in terms of molecular and nutritional composition response, beside it is indispensable to think more and more on effect of contaminants along the food web system. In this study, Sparus aurata specimens were exposed for 15 days, by diet, to a mixture of carbamazepine (Cbz), polybrominated diphenyl ether-47 (PBDE-47) and cadmium chloride (CdCl₂), at two doses (0.375 μg g-1 D1; 37.5 μg g-1 D2) (T15). After, fish were fed with a control diet, without contaminants mix, for other 15 days (T30). The study explored the effect on oxidative stress in the liver, analyzing specific molecular markers and effects on quality, by fatty acid profile and lipid peroxidation. Molecular markers involved in ROS scavenging, such as superoxide dismutase (sod), catalase (cat) and glutathione peroxidase (gpx) were evaluated by gene expression; as markers of quality and lipid peroxidation, the fatty acids (FAs) profile and the level of malondyaldeide (MDA) were assessed. Sod and cat genes underwent to up-regulation after 15 days of diet containing contaminants and showed down-regulation after the next 2 weeks of detoxification (T30). At T15, the FAs profile showed an increase of the saturated fatty acids (SFA), and a decrease of the polyunsatured fatty acids (PUFA). The MDA levels increased over time, indicating an ongoing radical damage. These results suggest that the effects of the contaminants can be perceived not only at molecular but also at nutritional level and that the molecular and biochemical markers adopted could be differently used to monitor the health of aquatic organisms in the marine environment.

Cadmium effects on the freshwater teleost Prochilodus lineatus: Accumulation and biochemical, genotoxic, and behavioural biomarkers

In order to evaluate the effects of Cd, juveniles of the Neotropical fish Prochilodus lineatus were exposed to 1 and 10 μg L^-1 Cd, for 24 and 96 h. Fish exposed to Cd showed metal accumulation in the gills, kidney, and liver, an increase in DNA damage in erythrocytes, and an increase in lipid peroxidation (LPO) in the kidney. Cd exposure also caused a reduction in catalase activity, metallothionein induction, and LPO in the liver. Cd stimulated the swimming activity of exposed fish, resulting in longer swimming times and distances travelled, especially for the shortest exposure time. Changes in acetylcholinesterase activity (AChE) in the muscle and brain are probably related to these behavioural responses. These results show that Cd affects the functioning of several organs in P. lineatus, which is indicated by the genotoxic damage and changes in the AChE and swimming pattern of the exposed fish.

Chronic hypoxia and Cu2+ exposure induce gill remodeling of largemouth bass through endoplasmic reticulum stress, mitochondrial damage and apoptosis

Hypoxia and Cu²⁺ pollution often occur simultaneously in aquatic ecosystems and jointly affect physiology of fish. As the respiratory and ion exchange tissue of fish, how gill responds to the stress induced by these two abiotic environmental factors is still unclear. We have conducted a study by exposing largemouth bass (Micropterus salmoides) to hypoxia (2.0 mg·L^-1) and/or Cu²⁺ (0.5 mg·L^-1) for 28 days to answer this question. We subsequently studied respiratory rate, Cu²⁺ transport, endoplasmic reticulum (ER) stress, mitochondrial damage, and morphology in gill tissue on day 7, 14, 21 and 28. We found that hypoxia exposure increased the respiratory rate of largemouth bass, reflecting the response of largemouth bass to cope with hypoxia. Of note, Cu²⁺ entered gill by specifically binding to CTR1 and its accumulation dramatically in gill disrupted the response of largemouth bass to hypoxia. Hypoxia and/or Cu²⁺ exposure led to ER stress and mitochondrial damage in gills of largemouth bass. ER stress and mitochondrial damage induced apoptosis by activating caspase-8 and caspase-9 signaling pathways, respectively. Apoptosis induced by hypoxia and Cu²⁺ exposure had a positive and synergistic effect on gill remodeling by reducing interlamellar cell masses. In addition, Cu²⁺ exposure induced hypoxia-like remodeling to gill morphology through mechanisms similar to hypoxia exposure. Most of gene expression changed mainly within 21 days and recovered to the control level on day 28, reflecting the acclimation of largemouth bass to hypoxia and/or Cu²⁺ exposure at gene expression level. Overall, our research suggests that chronic hypoxia and Cu²⁺ exposure could induce gill remodeling of largemouth bass through ER stress, mitochondrial damage and apoptosis. The outcomes could provide an insight for fish environmental adaptation and environmental toxicology.

Effects on Bioaccumulation, Growth Performance, Hematological Parameters, Plasma Components, and Antioxidant Responses in Starry Flounder (Platichthys stellatus) Exposed to Dietary Cadmium and Ascorbic Acid

This study evaluates the toxic effects of dietary Cd and mitigative effects of AsA supplementation by measuring the growth performance, bioaccumulation, hematological parameters, plasma components, and antioxidant responses of Starry flounder (Platichthys stellatus). Platichthys stellatus (mean weight, 69.5 ± 1.4 g; mean length, 18.2 ± 0.21 cm) was fed with dietary cadmium-ascorbic acid (Cd-AsA) composed of C₀A₀, C₀A₅₀₀, C₀A₁₀₀₀, C₄₀A₀, C₄₀A₅₀₀, C₄₀A₁₀₀₀, C₈₀A₀, C₈₀A₅₀₀, and C₈₀A₁₀₀₀ mg of Cd-AsA per kg diet for four weeks. Our results showed that Cd accumulation significantly increased in proportion to the Cd concentration, where the highest levels were observed in the intestine, followed by the kidney, liver, and gills. Dietary AsA significantly mitigated the Cd accumulation in all tissues, and the reduction in Cd accumulation was proportional to the increase in AsA concentration. Dietary Cd has adverse effects on growth performance (body weight gain, specific growth rate, feed conversion ratio, and hepatosomatic index) and can alter the hematological parameters (red blood cell count, hematocrit, and hemoglobin), plasma components (glucose, total protein, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase), and antioxidant responses (superoxide dismutase, catalase, glutathione S-transferase, and glutathione). Dietary AsA restored the decreased growth performance parameters and the altered hematological parameters, plasma components, and antioxidant responses caused by the dietary Cd exposure. The results of this study showed that dietary Cd is toxic to P. stellatus, while dietary AsA is effective in mitigating the toxic effects of Cd.

Sublethal Effects of Cadmium on the Osmoregulatory and Acid-Base Parameters of Tilapia (Oreochromis niloticus) at Various Times

Background

Cadmium (Cd) can contaminate aquatic environments as a result of anthropogenic activity. Cd accumulates quickly in the tissues of fish and has the potential to affect their physiology, including osmoregulation and acid-base balance. Therefore, the purpose of this study was to examine the sublethal effects of Cd on the osmoregulation and acid-base balance of tilapia Oreochromis niloticus at different times.

Methods

Fish were exposed to sublethal concentrations of Cd (1 and 2 mg/L) for 4 and 15 days. At the end of the experiment, fish were collected from each treatment to examine the levels of Cd and carbonic anhydrase (CA) in the gills, plasma osmolality, ions, blood pH, pCO₂, pO₂, and hematological parameters.

Results

Cd concentrations in gills rose with increasing Cd concentrations in the medium and exposure time. Cd inhibited respiration by generating metabolic acidosis, decreasing gill CA, reducing pO₂, plasma osmolality, Cl^-, and K⁺, particularly at 2 mg/L for 4 days and 1 and 2 mg/L for 15 days. Red blood cell (RBC), hemoglobin (Hb), and hematocrit (Ht) levels decreased as Cd levels in water and exposure duration increased.

Conclusion

Cd inhibits respiration, lowers RCB, Hb, and Ht levels and decreases ionic and osmotic regulation. All of these impairments can limit a fish's ability to provide appropriate oxygen to its cells, hence diminishing its physical activity and productivity.

Diet supplementation of astaxanthin mitigates cadmium induced negative effects on oxidative, inflammatory and non-specific immune responses, and the intestinal morphology in Trachinotus ovatus

Knowledge about additive on alleviating the negative effects of fish exposed to cadmium (Cd) needs to be more identified in the aquaculture. Therefore, the present study aims to investigate whether diet supplemented with astaxanthin could mitigate adverse effects on hepatic Cd deposition, oxidative, inflammatory and non-specific immune responses, and intestinal morphology of Trachinotus ovatus exposed to dietary Cd treatment. Three isonitrogen-isolipid experimental diets supplemented with/without CdCl₂/Astaxanthin were formulated to feed the T. ovatus for 30 days. Results demonstrated that considerably higher hepatic Cd level was found in two Cd supplementing groups compared to the control group (p < 0.05), while no statistical difference of hepatic Cd concentration between these two Cd supplementing groups (p > 0.05). The activity of hepatic total superoxide dismutase, RNA expression levels of hepatic Nrf2-keap1 pathway genes, pro-inflammatory genes, and non-specific immune genes were no statistical differences between the control group and the dietary Cd supplementing group (p > 0.05), while these data in the dietary Cd with astaxanthin group showed significantly higher than that in the dietary Cd without astaxanthin group (p < 0.05). On the contrary, hepatic malondialdehyde content in the dietary Cd group showed significantly higher than that in the control group and dietary Cd with astaxanthin group (p < 0.05). Significantly lower mid-intestine morphology parameters were obtained in the dietary Cd group than the control group (p < 0.05), while significantly higher data were found in the dietary Cd with astaxanthin group compared to the dietary Cd group (p < 0.05). These results indicated that astaxanthin could mitigate the inhibitory effects of Cd on the oxidative, inflammatory and non-specific immune responses, and intestinal morphology of T. ovatus while not reduce the hepatic Cd deposition.

Can Lemna minor mitigate the effects of cadmium and nickel exposure in a Neotropical fish?

We aimed to evaluate if Lemna minor can mitigate the observed effects of cadmium (Cd) and nickel (Ni) exposure in Prochilodus lineatus. Fish were exposed for 96 h to 20 µg L^-1 of Cd, 1.5 mg L^-1 of Ni, or to a mixture of these two metals. In all tests, one group was exposed to the metals with duckweed on the water surface, and other group was exposed only to the metals, without plants. After each exposure, samples of P. lineatus tissues were collected to evaluate multiple biomarkers. Duckweed prevented bioaccumulation in some fish tissues and attenuated changes in acetylcholinesterase activity, increases in erythrocytic nuclear abnormality frequency, and hyperglycemia. However, the changes in plasma ion concentrations, reduction in activity of ion transport enzymes, and histological damage were not mitigated. Therefore, we concluded that L. minor partially attenuates the effects caused by Cd and Ni exposure.

Impacts of tailings of Fundão dam (Brazil) rupture on marine fish: Metals bioaccumulation and physiological responses

This study evaluated the impacts of the mining tailings after the rupture of the Fundão dam on fish communities on the Atlantic Ocean southeast coast. Four sample collections were carried out over two years (2018-2020), in seasonal periods. Omnivorous/herbivorous and carnivorous fish were collected for analysis of metal bioaccumulation, multibiomarkers of environmental contamination and histopathology. Metal bioaccumulation was stronger correlated in carnivorous fish in the dry-2018 collection, besides higher activity of antioxidant enzymes, energy metabolism and higher morphological damage; however, there was less oxidative damage and less metallothioneins induction, and these variables were strongly associated with the wet-2020 collection. In a temporal view, it was possible to observe a reduction in metal levels in fish, except in the mouth of the Doce River. These events can be explained by seasonal natural events, which tend the resuspension and boost metal levels, mainly in the mouth region during the rainy season.

Combined effects of polystyrene microplastics and cadmium on oxidative stress, apoptosis, and GH/IGF axis in zebrafish early life stages

The toxicological interactions of microplastics (MPs) and heavy metals have been paid much attention in aquatic organism. The mechanisms are not fully clear, particularly in fish early life stages. To the end, zebrafish embryos were exposed to 500 μg/L MPs, 5 μg/L cadmium (Cd), and their combination for 30 days. Body weight, adsorption characteristics of Cd onto MPs, Cd accumulation, oxidative stress, apoptosis, and growth hormone/insulin-like growth factor-I (GH/IGF) axis were examined. Exposure to MPs and Cd alone reduced body weight, which was aggravated by co-exposure. An increase in reactive oxygen species (ROS) levels was observed in larvae exposed to Cd or MPs + Cd, suggesting an induction of oxidative stress. Lipid peroxidation levels were not affected by exposure to MPs and Cd alone but dramatically enhanced by co-exposure, which may be explained by the reduction of total antioxidant capacity (TAOC) and activity levels of Mn-superoxide dismutase (Mn-SOD) and catalase (CAT) after co-exposure. Increased apoptotic cells were observed in the vertebral body of larvae exposed to Cd, the esophagus of larvae exposed to MPs, and both organs of larvae exposed to MPs + Cd, which was further confirmed by changes in the activities of Caspase-3, Caspase-8 and Caspase-9. PCR array on the transcription of genes related to growth, oxidative stress and apoptosis was examined, showing that the combined exposure resulted in greater magnitude of changes than MPs and Cd alone. The results indicate that MPs can enhance the negative effects of Cd on growth, oxidative damage and apoptosis in early life stages of zebrafish. However, the adsorption of Cd onto MPs was not observed and the combined exposure did not increase the Cd content in larvae compared to the single Cd exposure, implying that vector role of MPs in Cd uptake is negligible.

Hypoxia Induces Oxidative Injury and Apoptosis via Mediating the Nrf-2/Hippo Pathway in Blood Cells of Largemouth Bass (Micropterus salmoides)

Investigating how aquatic animals respond to hypoxia brought about by changes in environmental temperature may be of great significance to avoid oxidative injury and maintain the quality of farmed fish in the background of global warming. Here, we investigated the effects of hypoxia on oxidative injury and environment-sensing pathway in blood cells of Micropterus salmoides. The total blood cell count (TBCC) and Giemsa staining showed that hypoxia could lead to damage of blood cells. Flow cytometry analysis confirmed that the apoptosis rate, Ca2+ level, NO production and ROS of blood cells were significantly increased under hypoxia stress. Environment-sensing pathways, such as Nrf2 pathway showed that hypoxia resulted in significant up-regulation of hiF-1 alpha subunit (Hif-1α), nuclear factor erythroid 2-related factor 2 (Nrf2) and kelch-1ike ECH- associated protein l (Keap1) expression. Meanwhile, the expression of Hippo pathway-related genes such as MOB kinase activator 1 (MOB1), large tumor suppressor homolog 1/2 (Lats1/2), yes-associated protein/transcriptional co-activator with PDZ-binding motif (YAP/TAZ), protein phosphatase 2A (PP2A) were significantly increased in blood cells after hypoxia exposure. In addition, hypoxia stress also increased the expression of catalase (CAT) and glutathione peroxidase (GPx), but decreased the expression of superoxide dismutase (SOD). Consequently, our results suggested that hypoxia could induce oxidative injury and apoptosis via mediating environment-sensing pathway such as Nrf2/Hippo pathway in blood cells of M. salmoides.

Transcriptome profiling reveals differential expression of immune-related genes in gills of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) under hypoxic stress: Potential NLR-mediated immune response

Fish gills are the primary organ that respond to sudden changes in the dissolved oxygen (DO) level in the aquatic environment. Hypoxic stress impairs the normal function of gill tissues. However, little is known about the mechanisms of the response of yellow catfish gills to hypoxic stress. In this study, we compared transcriptomic and physiological changes in gill tissues of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) between a hypoxia-treated group (DO: 1.5 mg/L) and a control group (DO: 6.5 mg/L). In fish in the hypoxia-treated group, gill filaments underwent adaptive changes, and the number of vacuoles in gill tissues increased. Exposure to hypoxic conditions for 96 h resulted in increased anaerobic metabolism and decreased antioxidant and immune capacity in gill tissues. Transcriptome analyses revealed 1556 differentially expressed genes, including 316 up-regulated and 1240 down-regulated genes, between fish in the hypoxia-treated and control groups. Functional analyses indicated that the main pathway enriched with differentially expressed genes was immune response, followed by energy metabolism and signal transduction. Under hypoxic stress, the transcript levels of genes involved in the NOD-like receptor signaling pathway initially increased rapidly but then decreased over time, suggesting that the NOD-like receptor-mediated immune response plays an essential role in hypoxia tolerance and resistance in hybrid yellow catfish. Our results provide novel insights into which immune-related genes and pathways are activated under hypoxic stress, and reveal details of early adaptation of the immune response and defense mechanisms under hypoxic stress.

Nurse sharks, space rockets and cargo ships: Metals and oxidative stress in a benthic, resident and large-sized mesopredator, Ginglymostoma cirratum

It is widely recognized that apex predators, such as large sharks with highly migratory behavior, are particularly vulnerable to pollution, mainly due to biomagnification processes. However, in highly impacted areas, mesopredator sharks with resident behavior can be as vulnerable as apex sharks. In this context, this study evaluated cadmium (Cd), mercury (Hg), lead (Pb), and rubidium (Rb) concentrations, as well as the potentially protective effects of selenium (Se) and the behavior of two non-enzymatic biomarkers, metallothionein (MT) and reduced glutathione (GSH), employing the Atlantic nurse shark Ginglymostoma cirratum as a study model and compared the results with other resident benthic sharks, as well as highly mobile apex sharks. Muscle tissue samples from 28 nurse sharks opportunistically sampled from the Brazilian Amazon Coast were analyzed. Lower metal concentrations were observed for Pb, Rb and Se in the rainy season, while statistically significant correlations between metals were observed only between Hg and Cd and Pb and Se. Molar ratio calculations indicate potential protective Se effects against Pb, but not against Cd and Hg. No associations between MT and the determined metals were observed, indicating a lack of detoxification processes via the MT detoxification route. The same was noted for GSH, indicating no induction of this primary cellular antioxidant defense. Our results indicate that benthic/mesopredator sharks with resident behavior are, in fact, as impacted as highly mobile apex predators, with the traditional detoxification pathways seemingly inefficient for the investigated species. Moreover, considering the studied population and other literature data, pollution should be listed as a threat to the species in future risk assessments.

Antioxidant and antigenotoxic potential of Morinda tinctoria Roxb. leaf extract succeeding cadmium exposure in Asian catfish, Pangasius sutchi

The present study investigated the protective effect of methanolic leaf extract of Morinda tinctoria. Roxb (MEMT) (200 mg/kg) via feed in supplementation with standard compound silymarin (400 mg/kg). M. tinctoria (Roxb.) belonging to Rubiaceae, is an evergreen shrub indigenous to unfarmed lands of tropical countries. It is considered as an essential traditional medicine attributing for the potential antioxidant and anti-inflammatory properties. The enhancements of antioxidant and antigenotoxic status in different tissues of cadmium (Cd) intoxicated Pangasius sutchi were evaluated by using various antioxidant assays (superoxide dismutase (SOD) and catalase (CAT) and lipid peroxidation) in addition to micronuclei (MN), binuclei (BN) and comet assay. The cadmium toxicated fish showed a significant (p < 0.001) increase in lipid peroxidation (LPO) activities in liver, gills, muscle and kidney whereas significant (p < 0.001) decline were observed in superoxide dismutase (SOD) and catalase (CAT) contents in all fish tissues. The results also revealed that, Cd exposure induced the formation of genotoxic endpoints like MN, BN, notched nuclei, kidney shaped nuclei and DNA damage in the fish erythrocytes. Maximum of 26.8% MN frequencies and maximum of 66.74% tail DNA damage were observed on the 7th day of Cd exposure. A time-dependent significant increase (p < 0.001) in the frequencies of MN, BN and tail DNA damage were observed in all treated groups against the control which started to decline from 14th day onwards. There was a decline in the LPO content, frequencies of MN, BN and percentage of tail DNA in contrast to significant elevation in SOD and CAT content in all tissues due to the combined treatment of M. tinctoria feed and water borne Cd exposure. It can be concluded from our observations that, supplementation of M. tinctoria leaf extract through feed alone produced enhanced antioxidant and antigenotoxic status in cadmium treated fish by diminishing oxidative stress and genotoxicity effects in a time dependent manner.

Dietary exposure to methyl mercury chloride induces alterations in hematology, biochemical parameters, and mRNA expression of antioxidant enzymes and metallothionein in Nile tilapia

Methyl mercury chloride "MMC" (CH₃ClHg) is an ubiquitous environmental toxicant that causes a variety of adverse effects. In the present study, we investigated the effects of sub-chronic toxicity of MMC on Nile tilapia (Oreochromis niloticus) through the evaluation of growth performance and hematological, biochemical, and oxidative stress biomarkers. From 150 healthy fish, five equally sized treatment groups were created: a control (CT) group fed with a basal diet and four MMC treatment groups exposed to 0.5, 1, 1.5, and 2 mg of MMC per kg of basal diet for 60 days. MMC exposure significantly reduced the growth performance and survival of O. niloticus and decreased red blood cell count and hemoglobin concentration. Treated fish exhibited normocytic normochromic anemia in addition to leucopenia, lymphopenia, granulocytopenia, and monocytopenia. Moreover, MMC exposure significantly affected liver function, including a reduction in the total protein levels while increasing cholesterol and triglyceride levels. It also markedly increased the production of stress biomarkers such as glucose and cortisol levels. Furthermore, MMC significantly elevated the levels of hepatic enzymes, induced tissue damage, and caused inflammation, as indicated by the upregulation of mRNA expression of hepatic metallothionein. Finally, MMC exposure induced oxidative stress by altering the antioxidant status of the liver and downregulating the mRNA expression of superoxide dismutase, glutathione peroxidase, and glutathione S-reductase. In conclusion, MMC toxicity induced hematological and biochemical alterations, leading to an enhanced state of oxidative stress in O. niloticus.

Study on the impacts of chemical and green synthesized (Leucas aspera and oxy-cyclodextrin complex) dietary zinc oxide nanoparticles in Nile tilapia (Oreochromis niloticus)

The present study was designed to evaluate the health effects of dietary nanozinc prepared by two methods: conventional chemical method and green method. The parameters evaluated were the extent of bioaccumulation, antioxidant status, histological, immunological changes and DNA damage in Nile tilapia fed nanozinc feed. Zinc oxide nanoparticles were first prepared by green and chemical methods. Before feed preparation, the in vitro antioxidant activity and antibacterial activity of both types of nanoparticle solutions were tested and the results revealed enhanced activities in green synthesized ZnO NP solution. After the acclimatization period, 420 Nile tilapias were distributed randomly into 21 glass tanks with 20 fish per tank in triplicates. Fish were fed control diet without any ZnO NP and (i) GT1-green synthesized ZnO NP diet at 100 mg/kg, (ii) CT1-chemically synthesized ZnO NP diet at 100 mg/kg, (iii) GT2-green synthesized ZnO NP diet at 200 mg/kg, (iv) CT2-chemically synthesized ZnO NP diet at 200 mg/kg, (v) GT3-green synthesized ZnO NP diet at 400 mg/kg and (vi) CT3-chemically synthesized ZnO NP diet at 400 mg/kg for 60 days. After 60 days, gill and liver samples were collected for analysing oxidative stress, histopathological alterations and bioaccumulation of zinc, whereas serum samples were collected for evaluating immune response. The results revealed that the GT3 diet significantly (P < 0.05) enhanced the level of antioxidant enzymes (CAT, SOD, GPx, GR and GSH) than dietary nanozinc prepared by the chemical method. Similarly, the innate immunological parameters were significantly (P < 0.05) augmented in fish fed GT3 diet. Comparative histological study of liver and gill tissues revealed normal architecture in the tissues of fish fed green synthesized NP-enriched feed, whereas the tissues of fish fed chemically synthesized NP feed exhibited histological alterations. Bioaccumulation of zinc was more in the liver followed by the muscle and least in the gills and DNA damage was more evident in fish fed chemically synthesized ZnO NP-enriched feed. In conclusion, the results suggest that the inclusion of 400 mg/kg GT3 diet in fish diet enhanced the level of antioxidant enzymes, boosted immune response and did not cause histological damage to organs, and therefore, GT3 nanofeed can be recommended for fish health improvement.

Sediment contamination and toxic effects on Violet Goby fish (Gobioides broussonnetii - Gobiidae) from a marine protected area in South Atlantic

The Estuarine-Lagoon Complex of Iguape-Cananéia (ELCIC), a Marine Protected Area (MPA) in Brazil, was the focus of this study that aimed to relate external levels of exposure to contaminants to toxic effects on Gobioides broussonnetii fish. Different anthropogenic contaminants such as metals, polycyclic aromatic hydrocarbons (PAHs) and pharmaceuticals and personal care products (PPCPs) were analyzed in the sediments; and biochemical, histopathological and genotoxicity biomarkers evaluated in fish; in two different seasons at three sites of the estuarine region. Higher contamination of the sediments was observed near the main urban center (Iguape city - IG). Metal concentrations were considered low to moderate, while PAHs concentrations were considered low. The concentrations of PPCPs increased due to the anthropogenic presence and were higher near IG and the Cananéia Island (CI). Contributions from historical mining, agriculture, nautical activities, oil, sewage and waste disposal, biomass and fossil fuels combustion were identified. Higher concentrations of metals and PPCPs were observed during the cold-dry season, suggesting influences of the lower hydrodynamics during the season of lower precipitation. Higher PAHs concentrations occurred in the hot-rainy season, indicating influences of greater human presence in summer. In fish, biological responses followed the same spatial and seasonal pattern. More pronounced changes in antioxidant, biotransformation, histopathological and genotoxic biomarkers were observed in IG and CI. The multivariate analysis and the integrated biomarkers response index (IBR) also evidenced worse environmental conditions in these sites. This result can indicate a negative influence of anthropogenic activities on the contamination of sediments and on the biological responses of fish. This study presented the first ecotoxicological data for the species and suggested that these chronic exposures can cause adverse effects on this fish population. The data contribute to the understanding of local environmental quality and can be applied in the future to the environmental and social management of marine protected areas.

Integrated biomarker responses in oysters Crassostrea gasar as an approach for assessing aquatic pollution of a Brazilian estuary

The Laguna Estuarine System (LES), southern Brazil, suffers impacts from anthropogenic activities, releasing contaminants into the ecosystem. This study evaluated changes in biochemical and molecular biomarkers and contaminants concentrations in oysters Crassostrea gasar transplanted and kept for 1.5 and 7 days at three potentially contaminated sites (S1, S2, and S3) at LES. Metals varied spatiotemporally; S1 exhibited higher Ag and Pb concentrations, whereas Cd was present in S3. S2 was a transition site, impacted by Ag, Pb, or Cd, depending on the period. Organic contaminants concentrations were higher before transplantation, resulting in the downregulation of biotransformation genes transcripts levels. Phase II-related genes transcripts and metals showed positive correlations. Decreased levels of HSP90-like transcripts and antioxidant enzymes activity were related to increased pollutant loads. Integrated biomarker response index (IBR) analysis showed S1 and S3 as the most impacted sites after 1.5 and 7 days, respectively. Regardless of the scenario, LES contaminants pose a significant threat to aquatic biota.

Cadmium Accumulation and Kinetics in Solea senegalensis Tissues under Dietary and Water Exposure and the Link to Human Health

Bioaccumulation of cadmium was assessed in different tissues of the benthic fish Solea senegalensis. Juvenile Senegalese soles were simultaneously exposed to cadmium-contaminated diet (Hediste diversicolor) and water during 14 days and allowed to depurate for another 14 days. Cadmium content was measured in muscle, gills, liver and intestine, with recorded values increasing in these tissues in this same order. Muscle showed a considerably lower cadmium accumulation after 14 days of uptake. Cadmium kinetics in juvenile Senegalese soles revealed that the highest uptake flux of this metal occurred in the intestine. Cadmium depuration from the liver was not detected, which suggests the existence of a storage compartment for this metal in Solea senegalensis during uptake and depuration. Comparisons between maximum acceptable values for cadmium in the muscle, the Target Hazard Quotient and the Estimated Weekly Intake, indicated that acceptable limits were not exceeded, and the muscle of juvenile Senegalese soles could be considered safe for human consumption.

Distinct dietary cadmium toxic effects and defense strategies in two strains of gibel carp (Carassius gibelio) revealed by a comprehensive perspective

Previous studies demonstrated that gibel carp A strain was more susceptible to herpesvirus infection than other strains. Thus, we hypothesized that F strain might display better defense responses than the A strain against cadmium (Cd) exposure. To test our hypothesis, gibel carp A strain and F strain were exposed to three diets comprising of different concentrations of Cd for 8 weeks to compare their resistances to Cd. Comprehensive evaluations on biochemical, physiological and histological responses were conducted post-exposure. Results showed that no adverse effects and differences were observed on growth in two strains of gibel carp, compromising of the remarkable hepatoxicity-caused liver damage as shown by histological observations. Dietary Cd exposure stimulated antioxidant defense in the liver to counteract the Cd hepatoxicity, especially in the F strain. Activation of ER stress response positively stimulated the autophagy, then triggering apoptosis in fish after dietary Cd exposure. Thus, Cd-induced autophagy served as a protective strategy to alleviate hepatoxicity, but overaction of ER stress also triggered irreparable cell death via apoptosis. Cd induced dysregulation of lipid accumulation, which might be a common mechanism in response to hepatoxicity. Last but not least, the F strain showed stronger response on antioxidant, ER stress and autophagy, but apoptosis were remitted compared with the A strain, implying the F strain showed stronger response but better defense strategies to dietary Cd exposure. Our finding provides useful information for genetic breeding in aquaculture, and ultimately contribute to the safety assessment of aquatic products for human consumption.

Long-term variations in fish community structure under multiple stressors in a semi-closed marine ecosystem in the South China Sea

Daya Bay is an ecologically and economically crucial semi-closed bay along the southern coast of China. It is proven to be a stressed ecosystem and therefore obviously vulnerable to further extrinsic disturbance. This study used fish data from bottom-trawl surveys, conducted from 1985 to 2018, to analyze variations in the fish community structure over the past 30 years. The results showed that warm-water fish species were overwhelmingly dominant during all years, suggesting the bay's tropical to subtropical characteristic. By 2015, the number of fish species had decreased by 29.44% of that caught in 1987, moreover, values of the Shannon-Wiener diversity index and the Margalef richness index were lower in 2015 compared to 2004. There were evident shifts in the fish community composition from pelagic to demersal species, as suggested by the dominant species found in springtime, the dominant families, and percentages denoting the numbers of species in the main orders. Average fish body weight in landings declined from 13.4 g to 7.58 g, the body sizes of four typical commercial fish species decreased by varying degrees over the last 30 years. Abundance-biomass comparison curves suggested that the Daya Bay fish community was more stressed in 2015 than in 2004 during all seasons, except winter. In general, the fish community structure in Daya Bay is consequently in an unsteady state. Multiple anthropogenic disturbances, such as fishing (including overfishing and changes in the main fishing gears), the destruction of natural habitats, pollutants, and anthropogenically induced temperature changes, are likely to have caused obvious shifts in the bay's fish community structure. Therefore, we emphasize the need for integrating management of multiple anthropogenic stressors to achieve ecosystem-based management.

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.

iTRAQ-based proteomic analysis on the mitochondrial responses in gill tissues of juvenile olive flounder Paralichthys olivaceus exposed to cadmium

Cadmium (Cd) is an important heavy metal pollutant in the Bohai Sea. Mitochondria are recognized as the key target for Cd toxicity. However, mitochondrial responses to Cd have not been fully investigated in marine fishes. In this study, the mitochondrial responses were characterized in gills of juvenile flounder Paralichthys olivaceus treated with two environmentally relevant concentrations (5 and 50 μg/L) of Cd for 14 days by determination of mitochondrial membrane potential (MMP), observation of mitochondrial morphology and quantitative proteomic analysis. Both Cd treatments significantly decreased MMPs of mitochondria from flounder gills. Mitochondrial morphologies were altered in Cd-treated flounder samples, indicated by more and smaller mitochondria. iTRAQ-based proteomic analysis indicated that a total of 128 proteins were differentially expressed in both Cd treatments. These proteins were basically involved in various biological processes in gill mitochondria, including mitochondrial morphology and import, tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), primary bile acid biosynthesis, stress resistance and apoptosis. These results indicated that dynamic regulations of energy homeostasis, cholesterol metabolism, stress resistance, apoptosis, and mitochondrial morphology in gill mitochondria might play significant roles in response to Cd toxicity. Overall, this study provided a global view on mitochondrial toxicity of Cd in flounder gills using iTRAQ-based proteomics.

Effects of dietary yeast hydrolysate on the growth, antioxidant response, immune response and disease resistance of largemouth bass (Micropterus salmoides)

A 56-day growth trial was conducted to investigate the effects of dietary yeast hydrolysate on the growth performance, antioxidation, immune response and resistance against Aeromonas hydrophila in largemouth bass. Four experimental diets were prepared with yeast hydrolysate levels of 0% (Y0), 1.5% (Y1.5), 3.0% (Y3.0) and 4.5% (Y4.5). Each diet was randomly assigned to triplicate 150-L tanks and each tank was stocked with 30 largemouth bass (initial body weight, IBW = 7.71 ± 0.02 g). A challenge test was carried out after the feeding trial by injecting A. hydrophila intraperitoneally for 4-day observation. The results showed that the FBW and WGR in Y1.5 group were significantly higher than those in Y0 group (P < 0.05) and the feed conversion ratio (FCR) got the lowest value in Y1.5 group. And the hydrolysate supplement significantly increased the 4-day cumulative survival rate after the bacterial challenge (P < 0.05). The plasma malondialdehyde was lower in the yeast hydrolysate supplement groups in both pre- and post-challenge test (P < 0.05), while the plasma C3 increased (P < 0.05). In post-challenge test, the plasma superoxide dismutase (SOD) and catalase (CAT) activities increased in the Y1.5 and Y3.0 groups respectively (P < 0.05), and plasma lysozyme in Y1.5 group and the plasma IgM in Y3.0 group were higher than those in others respectively (P < 0.05). For the q-PCR results, in post-challenge test, the hepatic hep2 expression level in Y1.5 and Y4.5 groups were both significantly higher than those in others (P < 0.05), as well as il-8 in Y3.0 group. The spleen hif-1alpha and tgf-beta1 expression levels in Y4.5 group were all significantly lower than those in others (P < 0.05), while the gilt was significantly higher (P < 0.05) in the post-challenge test. And the expression levels of spleen tnf-alpah1 in Y1.5 and Y3.0 groups and il-8 in Y3.0 group were all significantly higher than those in other groups (P < 0.05) in the post-challenge test. The head kidney gilt expression level was significantly higher in the yeast hydrolysate supplement groups compared with the Y0 group (P < 0.05), and the head kidney il-8 expression level in Y1.5 group was significant higher than those in other groups in post-challenge test (P < 0.05). The present results indicated dietary yeast hydrolysate improved the antioxidant ability and enhanced the immune response of largemouth bass without negative effect on growth. And 1.5% or 3.0% of dietary yeast hydrolysate was recommended for largemouth bass based on the present results.

Temporal variations in kidney metal concentrations and their implications for retinoid metabolism and oxidative stress response in wild yellow perch (Perca flavescens)

The objective of this study was to determine if temporal variations in tissue metal concentrations are related to biomarkers of retinoid metabolism and oxidative stress responses in juvenile yellow perch (Perca flavescens). To this end, kidney metal (Cd, Cu and Zn) concentrations were measured in fish sampled in spring and fall 2012 in four lakes representing a wide range of water and sediment metal contamination in the Rouyn-Noranda (Quebec) region. Lakes Opasatica and Hélène were considered as reference lakes while lakes Dufault and Marlon were metal-contaminated. Kidney concentrations of Cd, Cu and Zn varied widely between spring and fall in fish from both clean and metal-contaminated lakes. An inter-lake difference in renal metal concentrations was only observed for Cd, with fish from Lake Marlon consistently displaying higher concentrations. In the spring, the concentrations of liver dehydroretinol, dehydroretinyl palmitate and total vitamin A esters were higher in fish sampled in the most contaminated lake. Strong temporal variations in the concentrations of these metabolites, as well as in the percentage of liver free dehydroretinol and the epidermal retinol dehydrogenase 2 transcription levels, were observed in fish living in the most metal-impacted lake, with generally higher values in the spring. In contrast to liver, in muscle, no clear seasonal variations in the concentrations of dehydroretinol, dehydroretinyl stearate or in the percentage of free dehydroretinol were observed in fish captured in the most contaminated lake. Temporal variations of traditional biomarkers of oxidative stress response were also observed in the most metal-impacted lake. For example, the transcription level of the gene encoding Cu/Zn superoxide dismutase-1 in liver and muscle catalase activity of perch sampled in the most contaminated lake were higher in spring than in fall. Positive relationships were found between kidney Cd concentrations and the transcription level of the gene encoding glucose 6-phosphate dehydrogenase, and all forms of retinoid concentrations in liver in spring, except with the percentage of free dehydroretinol where the correlation was negative. Our results translate to a state of stress caused by Cd and illustrate that temporal variations in tissue metal concentrations affect retinoid metabolism and antioxidant capacities in juvenile wild yellow perch. Overall this study contributes to highlight the importance of considering temporal variations when investigating the consequences of metal contamination on the physiology of wild fish.

The Chronic Exposure to Discharges of Sabal Drain Induces Oxidative Stress and Histopathological Alterations in Oreochromis niloticus

To study whether the effluents of Sabal drain could affect the health status of Oreochromis niloticus; site2 (south part of main canal), site3 (at the canal outlet), site4 (north part of main canal) and site1 (reference site) were selected. Compared to the reference fish, activities of superoxide dismutase and glutathione peroxidase in addition to glutathione reduced and thiobarbituric acid reactive substances concentrations of the gills showed significant (p < 0.05) increase with different levels in all studied sites. Whereas, catalase activities revealed significant (p < 0.05) decrease in all studied sites with maximum decrease in site3. The recorded histopathological lesions were correlated with the distance from discharge point. Gills, liver and kidney of site3 had the worst histopathological conditions based on the frequency of alterations appearance and size of the affected areas. While, the regressive alterations that recorded in site2 and site4 suggest the onset of adaptive histological mechanisms.

Effect of nitrite exposure on the antioxidant enzymes and glutathione system in the liver of bighead carp, Aristichthys nobilis

Nitrite (NO₂^-) can cause oxidative stress in aquatic animal when it accumulates in the organism, resulting in different toxic effects on fish. In the present study, we investigated the effects of nitrite exposure on the antioxidant enzymes and glutathione system in the liver of Bighead carp (Aristichthys nobilis). Fish [Initial average weight: (180.05 ± 0.092) g] were exposed to 48.634 mg/L nitrite for 96 h, and a subsequent 96 h for the recovery test. Fish livers were collected to assay antioxidant enzymes activity, hepatic structure and expression of genes after 0 h, 6 h, 12 h, 24 h, 48 h, 72 h, 96 h of exposure and12 h, 24 h, 48 h, 72 h, 96 h of recovery. The results showed that the activity of glutathione peroxidase (GSH-Px), glutathione S-transferase (GST), and glutathione reductase (GR) increased significantly in the early stages of nitrite exposure. The study also showed that nitrite significantly up-regulated the mRNA levels of glutathione peroxidase (GSH-Px), glutathione S-transferase (GST), and glutathione reductase (GR) after 6, 48, and 72 h of exposure respectively. Nitrite also increased the formation of malondialdehyde (MDA), oxidized glutathione (GSSG), and the activity of catalase (CAT). Nitrite was observed to reduce the activity of superoxide dismutase (SOD) and the level of glutathione (GSH). In the recovery test, GSH and the GSSG recovered but did not return to pre-stress levels. The results suggested that the glutathione system played important roles in nitrite-induced oxidative stress in fish. The bighead carp responds to oxidative stress by enhancing the activity of GSH-Px, GST, GR and up-regulating the expression level of GSH-Px, GST, GR, a whilst simultaneously maintaining the dynamic balance of GSH/GSSG. CAT was also indispensable. They could reduce the degree of lipid peroxidation, and ultimately protect the body from oxidative damage.

Oxidative Stress Parameters, Induction of Lipid Peroxidation, and ATPase Activity in the Liver and Kidney of Oreochromis niloticus Exposed to Lead and Mixtures of Lead and Zinc

The purpose of this investigation was to evaluate the effects of lead (Pb) and lead + zinc (Zn) combination on the oxidative stress, total ATPase and Pb accumulation in the tissues of Oreochromis niloticus (Linnaeus, 1758). The fish were exposed to 0.1 mg/L Pb (T1), 1.0 mg/L Pb (T2) and mixtures of 0.1 mg/L Pb and 0.5 mg/L Zn (M1); 1.0 mg/L Pb and 5.0 mg/L Zn (M2) for 7 and 21 days. Pb accumulation, total ATPase activity, several antioxidant enzyme activities such as catalase, glutathione peroxidase (GPX), glutathione S-transferase, glutathione reductase, and thiobarbituric acid reactive substances concentrations were measured in the liver and kidney tissues. Metal accumulation in the tissues was higher in Pb exposure compare with mixtures of Pb and Zn exposures. Beside the inhibition of liver GPX activity, general increases of antioxidant enzyme activities in the tissues were recorded after metal exposures. This investigation emphasizes the oxidative stress in O. niloticus caused by Pb, and adaptation of the organisms to the changes in enzyme activities.

Tissue-Specific Antioxidative Responses and Cadmium Accumulation in Silurus meridionalis Under Chronic Waterborne Cadmium Exposure

In this study, the oxidative damage, antioxidative responses and cadmium (Cd) accumulation in juvenile Silurus meridionalis were studied, after S. meridionalis were exposed to 0 (control), 62.5, 125, 250 and 500 µg Cd/L for 56 days. Cd accumulation, malondialdehyde, superoxide dismutase (SOD), catalase, glutathione (GSH) and total antioxidant capacity (T-AOC) were determined in gill, liver, kidney and intestine tissues. The results showed that the Cd accumulation in S. meridionalis was dose-dependent and tissue-specific, with the highest Cd content in the kidney, followed by the liver, gill, and intestine. Waterborne Cd stress in S. meridionalis was expressed as tissue-specific oxidative damage and antioxidant responses in gill, liver, kidney and intestine tissues. Waterborne Cd exposure induced the most significant oxidative damage in the gill, followed by the liver and kidney, while the intestine showed no sensitivity to waterborne Cd exposure. The antioxidants, such as SOD in the liver, kidney and intestine, as well as T-AOC and GSH in the gill, liver and kidney, were sensitive to waterborne Cd exposure.

Acute hypoxic stress: Effect on blood parameters, antioxidant enzymes, and expression of HIF-1alpha and GLUT-1 genes in largemouth bass (Micropterus salmoides)

Dissolved oxygen (DO) plays a crucial role in survival, growth, and normal physiological functions of aquatic organisms. Nevertheless, the mechanisms involved in hypoxic stress and adaptation have not been fully elucidated in Largemouth bass (Micropterus salmoides). To reveal the effect of acute hypoxia on Largemouth bass, we simulated acute hypoxia (DO: 1.2 ± 0.2 mg/L) in the laboratory and analyzed physiological parameters (RBCs, Hb, SOD, CAT, NA⁺/K⁺-ATPase, GPx, and MDA) and gene expression (HIF-1alpha and GLUT-1) in Largemouth bass exposed to various durations of acute hypoxia (0, 1, 2, 4, 8, 12, and 24 h). Our results indicated that acute hypoxic exposure significantly increased RBCs but decreased Hb. In addition, antioxidant enzyme activity was enhanced significantly in the liver and muscles at the initial stage of acute hypoxic exposure, but decreased significantly in gills during the entire process of hypoxic exposure. Furthermore, the expression levels of HIF-1alpha and GLUT-1 mRNA were significantly up-regulated in Largemouth bass under acute hypoxic exposure. In conclusion, our study provides a valuable basis for further elucidation of hypoxic adaptation and facilitates husbandry for an economically valuable species.

A protocol for identifying suitable biomarkers to assess fish health: A systematic review

Background

Biomarkers have been used extensively to provide the connection between external levels of contaminant exposure, internal levels of tissue contamination, and early adverse effects in organisms.

Objectives

To present a three-step protocol for identifying suitable biomarkers to assess fish health in coastal and marine ecosystems, using Gladstone Harbour (Australia) as a case study.

Methods

Prior to applying our protocol, clear working definitions for biomarkers were developed to ensure consistency with the global literature on fish health assessment. First, contaminants of concern were identified based on the presence of point and diffuse sources of pollution and available monitoring data for the ecosystem of interest. Second, suitable fish species were identified using fisheries dependent and independent data, and prioritised based on potential pathways of exposure to the contaminants of concern. Finally, a systematic and critical literature review was conducted on the use of biomarkers to assess the health of fish exposed to the contaminants of concern.

Results/Discussion

We present clear working definitions for bioaccumulation markers, biomarkers of exposure, biomarkers of effect and biomarkers of susceptibility. Based on emission and concentration information, seven metals were identified as contaminants of concern for Gladstone Harbour. Twenty out of 232 fish species were abundant enough to be potentially suitable for biomarker studies; five of these were prioritised based on potential pathways of exposure and susceptibility to metals. The literature search on biomarkers yielded 5,035 articles, of which 151met the inclusion criteria. Based on our review, the most suitable biomarkers include bioaccumulation markers, biomarkers of exposure (CYP1A, EROD, SOD, LPOX, HSP, MT, DNA strand breaks, micronuclei, apoptosis), and biomarkers of effect (histopathology, TAG:ST).

Conclusion

Our protocol outlines a clear pathway to identify suitable biomarkers to assess fish health in coastal and marine ecosystems, which can be applied to biomarker studies in aquatic ecosystems around the world.

Zebrafish: A Model for the Study of Toxicants Affecting Muscle Development and Function

The rapid progress in medicine, agriculture, and allied sciences has enabled the development of a large amount of potentially useful bioactive compounds, such as drugs and pesticides. However, there is another side of this phenomenon, which includes side effects and environmental pollution. To avoid or minimize the uncontrollable consequences of using the newly developed compounds, researchers seek a quick and effective means of their evaluation. In achieving this goal, the zebrafish (Danio rerio) has proven to be a highly useful tool, mostly because of its fast growth and development, as well as the ability to absorb the molecules diluted in water through its skin and gills. In this review, we focus on the reports concerning the application of zebrafish as a model for assessing the impact of toxicants on skeletal muscles, which share many structural and functional similarities among vertebrates, including zebrafish and humans.

Effects of ecologically relevant concentrations of cadmium in a freshwater fish

Sub-chronic effects of ecologically relevant concentrations of cadmium (Cd) were evaluated in the catfish Rhamdia quelen. The fish were exposed to Cd (0, 0.1, 1, 10 and 100μgL(-1)) for 15 days. Bioconcentration was observed in the liver of fish exposed to 10 and 100μgL(-1) of cadmium. The liver glutathione S-transferase activity decreased at 0.1 and 1μgL(-1) and increased at 100μgL(-1) and lipoperoxidation increased in all tested concentrations. Fish exposed to 0.1, 1 and 100µgL(-1) Cd presented increase in hepatic lesion index. In the kidney, the catalase activity and LPO reduced in all exposed groups. The gluthatione peroxidase, etoxiresorufin-O-deethylase activities and metallothionein increased at the highest concentration of Cd, but the level of reduced glutathione decreased. The genotoxicity was observed at 0.1 and 100μgL(-1). Neurotoxicity was not observed. The results showed that low concentrations (range of μgL(-1)) of Cd caused hepato-, nephro- and hematological alterations in this freshwater fish species.

Combined effects of temperature changes and metal contamination at different levels of biological organization in yellow perch

In this study, we measured the effects of temperature (9°C, 20°C, and 28°C), metal contamination (cadmium and nickel) and their interaction on yellow perch (Perca flavescens) using liver enzymatic and transcriptomic endpoints and biometric indices. Kidney metal concentrations increased with a rise of temperature. The biometric indices analysed (Fulton condition factor, pyloric cæca, hepatosomatic and gonadosomatic indices) generally decreased with an increase of temperature but not with metal contamination. At the enzymatic level, the activity of superoxide dismutase (SOD), involved in antioxidant response, was affected by both temperature and metal contamination, whereas the activity of glucose-6-phosphate dehydrogenase (G6PDH), involved in energy accumulation but also in antioxidant response, was only affected by metal exposure. The response of perch to the stressors at the transcriptional level differed from the metabolic response. In particular, the transcription level of the cco and g6pdh genes sharply decreased with increasing temperature, while the activities of the corresponding enzymes remained stable. The normal response of the transcription level of the apoptotic gene (diablo) to heat stress was also altered in metal-contaminated fish. The combination of metal and temperature stresses also modified the response of antioxidant metabolism induced by these stressors individually. This study contributes to a better understanding of the influences of natural stressors like temperature on biomarkers commonly used in ecotoxicological studies and will facilitate their interpretation in the context of multiple stressors characteristic of field situations.

Structural and functional changes in the zebrafish (Danio rerio) skeletal muscle after cadmium exposure

This report describes the alterations induced by an environmentally realistic concentration of cadmium in skeletal muscle fibre organization, composition, and function in the teleost zebrafish. Results demonstrate that the ion induces a significant quantitative and qualitative deterioration, disrupting sarcomeric pattern and altering glycoprotein composition. These events, together with a mitochondrial damage, result in a significant reduction in swimming performance. In conclusion, the evidence here collected indicate that in presence of an environmental cadmium contamination, important economic (yields in fisheries/aquaculture), consumer health (fish is an important source of proteins), and ecological (reduced fitness due to reduced swimming performance) consequences can be expected.

Effects of zinc oxide nanoparticles on bioaccumulation and oxidative stress in different organs of tilapia (Oreochromis niloticus)

Nano-size zinc oxide particles (ZnO NPs) are used in diverse industrial and commercial fields. However, the information from existing studies is not sufficient in evaluating the potential toxic effects of ZnO NPs. In this study, tilapia fish (Oreochromis niloticus) were exposed to different concentrations of small and large ZnO NPs in vivo. Accumulation in various organs/tissues (liver, gill, intestine, kidney, brain and muscle) and possible oxidative stress mechanisms were investigated comparatively. Fish were exposed to 1 and 10mg/L concentrations of small (10-30 nm) and large (100 nm) ZnO NPs semi-statically for 14 days. Both small and large ZnO NPs accumulated substantially in the tissues. Accumulation for the small ZnO NPs was significantly higher compared to larger NPs under same exposure regimes. Significant fluctuations were observed in antioxidant defense system biomarkers, including Superoxide dismutase (SOD), Catalase (CAT) and Glutathione (GSH) levels depending on particle size, exposure time and concentration. Lipid peroxidation measured with TBARS levels were higher in groups exposed to the suspensions of small ZnO NPs than that of large ZnO NPs and controls. These results imply that colloidal suspensions of small ZnO NPs induce elevated oxidative stress and toxic effects on tilapia compared to the larger NPs.

Antioxidant Responses and Nuclear Deformations in Freshwater Fish, Oreochromis niloticus, Facing Degraded Environmental Conditions

Two sites of collection along river Nile, nearby metal-related factories (site2) and 7 km downstream (site3) were compared to unpolluted reference fish farm (site1). Metals concentration (Cu, Zn, Pb, Fe, Mn and Cd) in water and sediment samples showed highly significant (p < 0.01) differences among sites. According to contamination factor and pollution load index values, overall pollution was ordered as site2 > site3 > site1. Compared with Oreochromis niloticus of site1, activities of superoxide dismutase, catalase and glutathione-S-transferase as well as malondialdehyde formation were significantly (p < 0.01) increased in both liver and gills of fish collected from metal contaminated sites. This increment showed a tissue-specific pattern with higher rate of increment in liver than in gills. While reduced glutathione level was sharply decreased in site2 and site3. Micronucleus test was assessed as an environmental genotoxic endpoint in erythrocytes. Assessment of eight nuclear deformations showed gradient frequencies related to the distance from the industrial discharges.

Estimation of seasonal risk caused by the intake of lead, mercury and cadmium through freshwater fish consumption from urban water reservoirs in arid areas of northern Mexico

Bioavailability and hence bioaccumulation of heavy metals in fish species depends on seasonal conditions causing different risks levels to human health during the lifetime. Mercury, cadmium and lead contents in fish from Chihuahua (Mexico) water reservoirs have been investigated to assess contamination levels and safety for consumers. Muscle samples of fish were collected across the seasons. Lead and cadmium were analyzed by inductively coupled plasma-optical emission spectrometry, and mercury by cold-vapor atomic absorption spectrometry. The highest concentrations of cadmium (0.235 mg/kg), mercury (0.744 mg/kg) and lead (4.298 mg/kg) exceeded the maximum levels set by European regulations and Codex Alimentarius. Lead concentrations found in fish from three water reservoirs also surpassed the limit of 1 mg/kg established by Mexican regulations. The provisional tolerable weekly intake (PTWI) suggested by the World Health Organization for methyl mercury (1.6 µg/kg bw per week) was exceeded in the spring season (1.94 µg/kg bw per week). This might put consumers at risk of mercury poisoning.

Effects of Cd injection on osmoregulation and stress indicators in freshwater Nile tilapia

Freshwater tilapia (Oreochromis niloticus) were intraperitoneally injected with sublethal doses of cadmium (1.25 or 2.5 mg Cd kg(-1) body mass) and sampled after 1, 4 and 7 days in order to evaluate the mechanisms of Cd toxicity at physiological and biochemical levels. Cd levels were significantly elevated in the gill and kidney following injection however levels in the kidney continued to accumulate while levels in the gill either did not change or decreased with time. Cd caused a generalized stress condition as indicated by an increase in blood glucose, lactate and cortisol levels as well as an oxidative stress indicated by increases in lipid peroxidation and protein carbonyl content. Furthermore, tilapia exhibited impairment in their osmoregulatory status based on the fall in plasma sodium levels. Concerning ion regulatory disruption, the kidney was the most affected organ since there was a generalized increase in renal Na(+)/K(+)-ATPase activity after 1 day of exposure to Cd followed by a significant decrease in day 7. This study provides some insights into the mechanisms of Cd toxicity at physiological and biochemical levels and complements previously reported findings on O. niloticus. The disruption of ion homeostasis, alterations in Na(+)/K(+)-ATPase activity and oxidative damage are the effects of Cd exposure that can be integrated in a comprehensive model for Cd impacts.

Acute effects of cadmium on osmoregulation of the freshwater teleost Prochilodus lineatus: enzymes activity and plasma ions

Cadmium (Cd) is a trace element that is very toxic to fish. It is commonly found in surface waters contaminated with industrial effluents. When dissolved in water, Cd can rapidly cause physiological changes in the gills and kidneys of freshwater fish. The objective of this study was to evaluate the acute effects of Cd on the osmoregulation of the Neotropical fish Prochilodus lineatus. Juvenile fish were exposed to Cd at two concentrations [1 (Cd1) and 10 (Cd10) μgL(-1)] for 24 and 96h. The effects of Cd were evaluated through the analysis of ions (Na(+), K(+), Ca(2+), and Cl(-)) and plasma osmolality, and by measuring the activities of enzymes involved in osmoregulation obtained from the gills and kidney. Fish exposed to Cd for 24 and 96h showed a decrease in Na(+)/K(+)-ATPase activity in the gills and kidney. The activity of carbonic anhydrase decreased in the gills after 24h and in both tissues after 96h of Cd exposure. The gill Ca(2+)-ATPase activity also decreased with Cd exposure, with a concomitant drop in the plasma concentration of Ca(2+). Despite the hypocalcemia, there were no changes in the concentration of the ions Na(+), K(+), and Cl(-) or in plasma osmolality. Among the enzymes involved in ion transport, H(+)-ATPase was the only enzyme that showed increased activity in gills, whereas its activity in kidney remained unchanged. The results of this study demonstrate that waterborne Cd at the maximum concentrations set by Brazilian guidelines for freshwater affects the gills and kidney functions of P. lineatus. Acute exposure to Cd resulted in the decrease of the activity of enzymes, which culminated with the loss of the fish's ability to regulate the levels of calcium in the blood, leading to hypocalcemia.

Acute effects of heavy metals on the expression of glutathione-related antioxidant genes in the marine ciliate Euplotes crassus

Euplotes crassus, a single-celled eukaryote, is directly affected by environmental contaminants. Here, exponentially cultured E. crassus were exposed to cadmium, copper, lead, and zinc and then the reactive oxygen species (ROS) and total glutathione (GSH) levels were measured. Subsequently, the transcriptional modulation of glutathione peroxidase (GPx) and glutathione reductase (GR) were estimated by quantitative RT-PCR. After an 8-h exposure, significantly higher increases in the relative ROS and total GSH levels were observed in exposed group, compared to the controls. Real-time PCR data revealed that the expression levels of GPx and GR mRNA were sensitively modulated within 8h of exposure to all heavy metals. These findings suggest that these genes may be involved in cellular defense mechanisms by modulating their gene expression against heavy metal-induced oxidative stress. Thus, they may be useful as potential molecular biomarkers to assess sediment environments for contaminants.