Exposure to waterborne copper reveals differences in oxidative stress response in three freshwater fish species

Effects of Hypoxia Stress on Survival, Antioxidant and Anaerobic Metabolic Enzymes, and Related Gene Expression of Red Swamp Crayfish Procambarus clarkii

The red swamp crayfish Procambarus clarkii is the most reared shrimp in China, but it is often affected by hypoxia stress in the process of seedling culture and adult crayfish culture. The oxygen consumption rate and asphyxiation point of juvenile crayfish (1.17 ± 0.03 g) and subadult crayfish (11.68 ± 0.11 g) at different temperatures (20, 22, 24, 26, and 28 °C) were studied. The survival, glycolysis, and expression of antioxidant genes were compared under 24 h acute hypoxia stress (1, 2, and 3 mg/L) and normal dissolved oxygen (7.5 mg/L). The results showed that the oxygen consumption rate and asphyxiation point of juvenile and subadult crayfish increased with increasing temperatures (20-28 °C). At the same temperature, the oxygen consumption rate and asphyxiation point of juvenile crayfish were significantly higher than those of subadult crayfish (p < 0.05). Within 24 h, the three hypoxia stress environments did not lead to the death of crayfish, indicating that P. clarkii has a strong ability to adapt to hypoxia. Hypoxia stress significantly affected the activities of antioxidant and anaerobic metabolic enzymes and gene expression in juvenile and subadult crayfish. The activities of the superoxide dismutase (SOD), catalase (CAT), and lactate dehydrogenase (LDH) and the content of lactic acid (LD) in the hepatopancreas of juvenile and subadult crayfish in the hypoxia stress groups increased significantly. The expression levels of SOD mRNA, CAT mRNA, Hsp70 mRNA, and crustin 4 mRNA in the hepatopancreas of juvenile and subadult crayfish in the hypoxia stress groups were significantly higher than those in the control group (p < 0.05), and the higher the degree of hypoxia stress, the higher the expression of each gene. The results showed that the antioxidant system of juvenile crayfish was more sensitive to hypoxia environments, and hypoxia stress resulted in increased stress levels in juvenile crayfish and subadult crayfish.

Toxicological effects of copper on bioaccumulation and mRNA expression of antioxidant, immune, and apoptosis-related genes in Chinese striped-necked turtle (Mauremys sinensis)

Heavy metals are among the most ubiquitous environmental pollutants of recent decades. Copper is commonly used to control algal blooms or macrophyte and waste infestations, its ambient concentration has increased significantly, indicating possible environmental risk. To investigate the effects of copper exposure on bioaccumulation, antioxidant defense, immune response, and apoptosis in the Chinese Striped-necked Turtle Mauremys sinensis, three experimental groups, control (0.0 mg/L), Cu2 (2 mg/L) and Cu4 (4 mg/L) were designed, and sampled at 14 and 28 days. Results showed that copper accumulates in different organs depending on the concentration and exposure time, Liver > Kidney > Gut > Heart > Brain > Muscle and the time order was 28 days > 14 days. The liver enzymes AST, ALT, and ALP decreased when the turtles were exposed to copper stress, while the contents of bilirubin TBIL, DBIL, IBIL, and LDH showed a significant upward trend. Similarly, the mRNA expression level of acetylcholinesterase AChE in the brain was significantly downregulated upon copper exposure. An upward trend was noticed in the liver Metallothionein MT mRNA expression levels compared to the control group. The mRNA expression levels of antioxidant enzymes CAT, SOD, MnSOD, and GSH-PX1 in the liver increased initially and then significantly decreased. Furthermore, the relative mRNA expression levels of inflammatory cytokines IL-1β, IL-8, TNF-α, and IFN-γ involved in inflammatory response significantly upregulated. Copper significantly increased the hepatic mRNA transcription of heat shock proteins HSP70 and HSP90 at different exposure durations. In addition, the relative mRNA levels of caspase3, caspase8, and caspase9 related to the caspase-dependent apoptotic pathway significantly increased under copper stress. These results explain that copper toxicity causes bioaccumulation, promotes oxidative stress, obstructs immunity, and induces inflammation and apoptosis by altering their gene expression levels in M. sinensis.

Rapid hyperthyroidism-induced adaptation of salmonid fish in response to environmental pollution

The streams draining volcanic landscapes are often characterized by a complex series of factors that negatively affect hydrobionts and lead to declines in their populations. However, in a number of cases, a range of rapid adaptive changes ensure the resilience of hydrobiont populations. Here, we present both field and experimental data shedding light on the physiological basis of adaptation to heavy metal contamination in populations of Dolly Varden charr (Salvelinus malma) differing in duration of isolation in volcanic streams. The study reveals that isolated populations have a physiological phenotype that distinguishes them from populations inhabiting clean waters. They are characterized by a hyperthyroid status accompanied by an increased metabolic rate, elevated activity of antioxidant enzymes, decreased ionic conductivity of tissues and reduced stored energy reserves. Our experimental data reveal that hyperthyroidism is an adaptive characteristic enhancing the resistance to heavy metal contamination and shaping the evolution of these populations. The similarity of physiological, developmental and morphological changes in isolated populations suggests a common source and mechanisms underpinning this case of 'evolutionary rescue'. Thus, populations of S. malma trapped in volcanic streams represent a genuine case of rapid endocrine-driven adaptation to changing environmental stimuli.

Biogenic Elements and Heavy Metals in Hermann's Tortoises-Testudo hermanni: Effect on Serum Biochemistry and Oxidative Status Parameters

BACKGROUND

Conservation of species diversity is the need of the hour for preserving life forms on Earth. Extinction of any part of the ecosystem has negative impacts on many processes and systems. The objective of this work was to analyze some biochemical and molecular indicators and their correlations to biogenic elements and heavy metals in Testudo hermanni (n = 16).

METHODS

Biochemical parameters were analyzed using the commercial kit DiaSys and biochemical analyzer Randox RX Monza. Sodium, potassium, and chlorides were measured using the EasyLite analyzer. Oxidative stress was evaluated using colorimetric and luminometric methods. Quantification of chemical elements in the blood was carried out using inductively coupled plasma mass spectrometry (ICPS).

RESULTS

Biochemical values of analyzed samples from Hermann's tortoises were almost the same as referential values described by multiple authors, with minor aberrations in the total protein parameter. Values of arsenic (As) and nickel (Ni) showed correlation with biochemical parameters and the parameters of oxidative stress. Cadmium (Cd) exhibited correlation with aspartate aminotransferase (AST).

CONCLUSIONS

This study reports correlations among four heavy metals, and their levels were again correlated with biochemical and molecular parameters in Hermann's tortoises.

Copper-induced Genotoxicity, Oxidative Stress, and Alteration in Transcriptional Level of Autophagy-associated Genes in Snakehead Fish Channa punctatus

Copper (Cu) is an essential and important trace element for some significant life processes for most organisms. However, an excessive amount of Cu can be highly toxic. The present study was conducted to elucidate the oxidative stress-induced alteration in transcriptional level of autophagy-related genes in the liver and kidney tissue of fish Channa punctatus after treatment with three different sublethal concentrations of CuSO₄ for 28 days. All the studied enzymatic and non-enzymatic oxidative stress markers viz. superoxide dismutase-SOD, catalase-CAT, glutathione peroxidase-GPx, glutathione reductase-GR, and glutathione-GSH showed an increase in their activity levels in the treated groups in a dose-dependent manner. Particularly SOD and CAT have shown a significant hike in activity levels. ROS levels in blood cells increased significantly (p < 0.05) in all the treated groups, i.e., Group II-1/20^th of 96 h-LC₅₀ (0.2 mg/L), Group III-1/10^th of 96 h-LC₅₀ (0.4 mg/L), and Group IV-1/5 ^h of 96 h-LC₅₀ (0.8 mg/L) of Cu²⁺ in a dose-dependent manner as compared to control (Group I). The upregulation in mRNA levels of autophagy-related genes Microtubule-associated protein 1 light chain 3 (LC3), Gamma-aminobutyric acid receptor-associated protein precursor (Gabarap), and Golgi-associated ATPase enhancer of 16 kDa (GATE16), autophagy-related 5 (ATG5) was observed while mammalian target of rapamycin (mTOR) showed downregulation in the liver and kidney tissue of fish. The decrease in mTOR and increase in ATG5 gene expression projects autophagic vesicle formation due to oxidative stress. There was significant induction in micronuclei (MN) frequency in all the treated groups. The highest frequency of MN induced by Cu²⁺ was recorded in Group IV after 28 days of the exposure period. Thus, it can be concluded that the available information about Cu²⁺-induced oxidative stress-mediated autophagy in the liver and kidney of fish C. punctatus remains largely unclear to date, so to fill the aforesaid gap, the present study was undertaken, which gives an insight for the mechanisms of autophagy induced by Cu²⁺ in fish.

Differences in toxicity and accumulation of metal from copper oxide nanomaterials compared to copper sulphate in zebrafish embryos: Delayed hatching, the chorion barrier and physiological effects

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish embryos were exposed to lethal concentrations of copper sulphate (CuSO₄) or copper oxide (CuO) ENMs (primary size ∼15 nm), and then the sub-lethal effects investigated at the LC₁₀ concentrations over 96 h. The 96 h-LC₅₀ (mean ± 95% CI) for CuSO₄ was 303 ± 14 µg Cu L^-1 compared to 53 ± 9.9 mg L^-1 of the whole material for CuO ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC₅₀ for hatching success was 76 ± 11 µg Cu L^-1 and 0.34 ± 0.78 mg L^-1 for CuSO₄ and CuO ENMs respectively. Failure to hatch was associated with bubbles and foam-looking perivitelline fluid (CuSO₄), or particulate material smothering the chorion (CuO ENMs). In the sub-lethal exposures, about 42% of the total Cu as CuSO₄ was internalised, as measured by Cu accumulation in the de-chorionated embryos, but for the ENMs exposures, nearly all (94%) of the total Cu was associated with chorion; indicating the chorion as an effective barrier to protect the embryo from the ENMs in the short term. Both forms of Cu exposure caused sodium (Na⁺) and calcium (Ca²⁺), but not magnesium (Mg²⁺), depletion from the embryos; and CuSO₄ caused some inhibition of the sodium pump (Na⁺/K⁺-ATPase) activity. Both forms of Cu exposure caused some loss of total glutathione (tGSH) in the embryos, but without induction of superoxide dismutase (SOD) activity. In conclusion, CuSO₄ was much more toxic than CuO ENMs to early life stage zebrafish, but there are subtle differences in the exposure and toxic mechanisms for each substance.

pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: Metal accumulation, antioxidant defenses and detoxification in livers

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO₂-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L^-1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO₂ ∼1353.89 μatm; extreme SA: pH 7.30, pCO₂ ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and detoxification in response to coexposure. Hepatic Cu accumulation (30.22-184.90 mg kg^-1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and detoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

A multi-biomarker approach to assess the sublethal effects of settleable atmospheric particulate matter from an industrial area on Nile tilapia (Oreochromis niloticus)

Iron and steel industries discharge a large amount of atmospheric particulate matter (PM) containing metals and metallic nanoparticles (NPs) that contaminate not only the air, but also settle into the aquatic environments. However, the effects of settleable atmospheric particulate matter (SePM) on aquatic fauna are still poorly understood. This study aimed to evaluate the sublethal effects of a short-term exposure to a realistic concentration of SePM on Nile tilapia (Oreochromis niloticus) using a multi-biomarker approach: relative ventricular mass (RVM) and heart function, blood oxidative stress, stress indicators, hemoglobin concentration, metallic NPs internalization, and metal bioaccumulation. Exposed fish exhibited reduced hemoglobin content and elevated plasma cortisol and glucose levels, reflecting stressed states. Furthermore, SePM caused blood oxidative stress increasing lipid and protein oxidation, decreasing glutathione levels, and inhibiting superoxide and glutathione reductase activities. SePM exposure also increased RVM and improved cardiac performance, increasing myocardial contractile force and rates of contraction and relaxation. In the heart tissue there was a significant accumulation of Fe > Zn > > Cr > Cu > Rb > Ni > V > Mn > Se > Mo > As. On the other hand, in the erythrocytes there was significant accumulation of Sn > Zn > > Cr > Ti > Mn = Ni > Nb > As > Bi. The highest bioaccumulation factors were found for Cr, Zn and Ni in both tissues. NPs (Ti, Sn, Al, Fe, Cu, Si, Zn) were also detected in ventricular myocardium of fish exposed and nanocrystallographic analysis revealed a predominance of anatase phase of TiO₂-NP, which is regarded to be more cytotoxic. The association between blood oxidative stress and energy expenditure to sustain increased cardiac pumping capacity under stress condition suggests that SePM has negative impacts on fish physiological performance, threatening their survival, growth rate and/or population establishment.

Copper-induced oxidative stress, transcriptome changes, intestinal microbiota, and histopathology of common carp (Cyprinus carpio)

Copper (Cu) is a common contaminant in aquatic environments, which could cause physiological dysfunction in aquatic organisms. However, few studies have comprehensively examined the impact of copper toxicity in freshwater fish over the past decade. In this research, the oxidative stress, liver transcriptome, intestinal microbiota, and histopathology of common carp (C. carpio) in response to Cu exposure were studied, by exposing juvenile carp to 0.2 mg/ml Cu²⁺ for 30 days. The results revealed that Cu²⁺ could induce significant changes in malondialdehyde (MDA) content and antioxidant enzyme (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)) activity. The changes in antioxidant enzyme activities indicate that Cu can induce oxidative stress by generating reactive oxygen species (ROS) content. RNA-seq analysis of the liver identified 1069 differentially expressed genes (DEGs) after treatment with 2.0 mg/L Cu²⁺. Among the DEGs, 490 genes were upregulated and 579 genes were downregulated. GO functional enrichment analysis revealed that Cu could affect the fatty acid biosynthetic process, carnitine biosynthetic process, and activity of carboxylic acid transmembrane transporter. Meanwhile, the most significantly enriched KEGG pathway also included the lipid metabolism pathway. In addition, Cu²⁺ exposure increased bacterial richness and changed bacterial composition. At the phylum level, we found that the ratio of Bacteroidetes to Firmicutes was increased in the treatment carps, which can regulate intestinal epithelium function and reduce inflammation and immune responses. At the genus level, the abundances of 11 genera were significantly altered after exposure to Cu²⁺. The altered composition of the microbial community caused by Cu exposure may play a useful role in compensation of the intestinal lesions by Cu exposure. Furthermore, we found that Cu²⁺ exposure could cause histological alterations such as structural damage to the liver and intestines. The results of this research contribute to a better understanding of mechanisms related to Cu toxicity in fish.

Toxicological damages on copper exposure to IgM+ B cells of Nile tilapia (Oreochromis niloticus) and mitigation of its adverse effects by β-glucan administration

Present investigation was carried out to study toxicological damages of copper exposure and mitigation of its adverse effects with β-glucan administration in IgM⁺ B cells which processes multiple roles similar to macrophages in Nile tilapia (Oreochromis niloticus). IgM⁺ B cells were pretreated with β-glucan (25 μg/mL) for 24 h before exposed to cupric oxide nanoparticles (CuO NPs) or cupric chloride (Cu ions) at the doses of 0, 5, 10, and 20 μg/mL for 24 h, respectively. Our results demonstrated that β-glucan increased reduced glutathione (GSH) to against oxidative damage from CuO NPs and Cu ions exposure in IgM⁺ B cells. The apoptosis process through mitochondrial signaling pathway was depressed in IgM⁺ B cells since the mitochondrial membrane potential (ΔΨm) was protected from copper exposure by β-glucan treatment. Furthermore, the inhibition on phagocytic abilities of IgM⁺ B cells caused by copper exposure could be enhanced with β-glucan treatment via evaluation of microspheres and bioparticles uptake and LPS-induced NO production. Importantly, β-glucan might participate in immunomodulation in IgM⁺ B cells through B cell antigen receptor (BCR) to suppress toxicological effect derived from copper exposure. Taken together, this study provides more information on the toxicological damages in IgM⁺ B cells upon copper exposure and explains the molecular mechanism to reverse adverse effects caused by copper exposure with β-glucan administration.

Toxicological effects of 6PPD and 6PPD quinone in zebrafish larvae

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is the most widely used antioxidant in automobile tyres and many rubber products. We investigated the impact of 6PPD and 6PPD quinone on acute toxicity, morphology, swimming behaviour, heart rate, and oxygen consumption in zebrafish larvae. Zebrafish embryos were exposed to 6PPD and 6PPD quinone at concentrations of 1, 10, and 25 µg/L during the development period of 1-96 hpf. In the present study, 6PPD quinone was found to be toxic to zebrafish larvae with a 24 h LC₅₀ of 308.67 µg/L. No significant mortality was observed at any of the tested concentrations. A dose-dependent reduction in swimming performance was observed in the exposed larvae at 116 hpf for both toxicants. Overall, our study shows that exposure of zebrafish embryos to 6PPD and 6PPD quinone at environmentally relevant concentrations (1 µg/L) does not affect its behaviour. However, exposure to higher but still sublethal concentrations of 6PPD and 6PPD quinone (10 and 25 µg/L) can affect behavioural endpoints. These findings reveal the toxicity of 6PPD and 6PPD quinone to early life stages of fish.

Toxicopathological impact of sub-lethal concentrations of lead nitrate on the gill of the catfish Heteropneustes fossilis

In recent studies, fish are heavily used as biomarkers of aquatic pollution, and heavy metals are among the main contributors to water pollution. In the present study, we investigated histopathological changes along with alterations in localization and activity of enzymes alkaline phosphatase (ALP), acid phosphatase (ACP), catalase (CAT), peroxidase (PER) and Na⁺/K⁺-ATPase in the gill tissues of Indian stinging catfish Heteropneustes fossilis exposed to two different concentrations (0.4 and 4 mg/L) of lead nitrate for 15 days. Histopathological examination of gill tissues revealed hypertrophy and swelling of epithelial cells, the fusion of epithelium of gill filaments and secondary lamellae, and alteration of secondary lamellae structure. Biochemical assays and histochemical localization show a pronounced effect on enzyme alkaline phosphatase activity and acid phosphatase in the gills of both groups of treated groups. In contrast, a significant decrease was noticed in the enzymatic response including catalase and peroxidase activity. Being a vital organ gill reflects the fish's physiological condition and the severity of the contamination in the surrounding environment. Gill is also the prime organ of osmoregulation in teleosts. Decreased activity of Na⁺/K⁺-ATPase suggests lead as a potent inhibitor of Na⁺/K⁺-ATPase that causes sodium hyperregulation. Alteration in the activity of metabolic enzymes reflects the level of tissue damage and metabolic disruption. At the same time, the increased activity of antioxidant enzymes states the condition of oxidative stress. Haematological parameters also altered with the lead nitrate exposure, reflecting metal toxicity and immune response against it. Meanwhile, this study also provides a potential use of H. fossilis as a biomarker for aquatic pollution.

β-glucan mitigation on toxicological effects in monocytes/macrophages of Nile tilapia (Oreochromis niloticus) following copper exposure

The protective effect of β-glucan against toxicological effects caused by copper oxide nanoparticles (Cu NPs) and copper ions (Cu ions) were studied in monocytes/macrophages (MO/MФ) of Nile tilapia (Oreochromis niloticus). Our results demonstrated that CuO NPs and Cu ions exposure aroused strong oxidative lesion in MO/MФ by detection of cellular reactive oxygen species (ROS) and reduced glutathione (GSH), as well as identification of several antioxidant-related cytokines. Meanwhile, the serious pro-inflammatory responses were accompanied during the processes of oxidative lesion by TNFα, IL-1β, and IL-6 genes validation. Copper induced MO/MФ underwent apoptosis through mitochondrial signaling pathway by mitochondrial membrane potential (ΔΨm) detection and Bax, Bcl-2, Cyt-c, Apaf-1, Caspase 9, Caspase 3 genes validation. Furthermore, the phagocytic abilities were inhibition in MO/MФ by evaluation of microspheres (0.5 and 1.0 μm beads) and bioparticles (S. agalactiae and A. hydrophila) uptake and LPS-induced NO production. However, β-glucan might participate in immunomodulation through C-type lectin receptor (CLR) and complement receptor 3 (CR3) to suppress pro-inflammatory responses, thereby revered all the copper induced aforementioned adverse effects in MO/MΦ. Taken together, our results provide insights on the mechanisms through β-glucan administration to mitigate toxicological effects of CuO NPs and Cu ions exposure to the MO/MΦ, which will benefit aspects related to fish farming and aquaculture production.

Anoxia-reoxygenation alters H2O2 efflux and sensitivity of redox centers to copper in heart mitochondria

Mitochondrial reactive oxygen species (ROS) have been implicated in organ damage caused by environmental stressors, prompting studies on the effect of oxygen deprivation and metal exposure on ROS metabolism. However, how anoxia and copper (Cu) jointly influence heart mitochondrial ROS metabolism is not understood. We used rainbow trout heart mitochondria to probe the effects of anoxia-reoxygenation and Cu on hydrogen peroxide (H₂O₂) emission during oxidation of palmitoylcarnitine (PC), succinate, or glutamate-malate. In addition, we examined the influence of anoxia-reoxygenation and Cu on site-specific H₂O₂ emission capacities and key antioxidant enzymes, glutathione peroxidase (GPx) and thioredoxin reductase (TrxR). Results showed that anoxia-reoxygenation suppressed H₂O₂ emission regardless of substrate type or duration of anoxia. Anoxia-reoxygenation reduced mitochondrial sensitivity to Cu during oxidation of succinate or glutamate-malate whereas high Cu concentration additively stimulated H₂O₂ emission in mitochondria oxidizing PC. Prolonged anoxia-reoxygenation stimulated H₂O₂ emission from sites O_F and I_F, inhibited emission from sites I_Q, II_F and III_Qo, and disparately altered the sensitivity of the sites to Cu. Interestingly, anoxia-reoxygenation increased GPx and TrxR activities, more prominently when reoxygenation followed a short duration of anoxia. Cu did not alter GPx but reduced TrxR activity in normoxic and anoxic-reoxygenated mitochondria. Overall, our study revealed potential mechanisms that may reduce oxidative damage associated with anoxia-reoxygenation and Cu exposure in heart mitochondria. The increased and decreased H₂O₂ emission from NADH/NAD⁺ and QH₂/Q isopotential sites, respectively, may represent a balance between H₂O₂ required for oxygen deprivation-induced signaling and prevention of ROS burst associated with anoxia-reoxygenation.

Nutrition and Metabolism of Minerals in Fish

Simple Summary

Our aim is to introduce the mineral nutrition of fish and explain the complexity of determining requirements for these elements, which are absorbed and excreted by the fish into the surrounding water. To date, only the requirements for nine minerals have been investigated. The review is focused on the absorption and the dietary factors that reduce their absorption from feed ingredients of plant and animal origin. Some diseases, such as cataracts, anemia and bone deformity, have been linked to dietary deficiency of minerals.

Abstract

Aquatic animals have unique physiological mechanisms to absorb and retain minerals from their diets and water. Research and development in the area of mineral nutrition of farmed fish and crustaceans have been relatively slow and major gaps exist in the knowledge of trace element requirements, physiological functions and bioavailability from feed ingredients. Quantitative dietary requirements have been reported for three macroelements (calcium, phosphorus and magnesium) and six trace minerals (zinc, iron, copper, manganese, iodine and selenium) for selected fish species. Mineral deficiency signs in fish include reduced bone mineralization, anorexia, lens cataracts (zinc), skeletal deformities (phosphorus, magnesium, zinc), fin erosion (copper, zinc), nephrocalcinosis (magnesium deficiency, selenium toxicity), thyroid hyperplasia (iodine), muscular dystrophy (selenium) and hypochromic microcytic anemia (iron). An excessive intake of minerals from either diet or gill uptake causes toxicity and therefore a fine balance between mineral deficiency and toxicity is vital for aquatic organisms to maintain their homeostasis, either through increased absorption or excretion. Release of minerals from uneaten or undigested feed and from urinary excretion can cause eutrophication of natural waters, which requires additional consideration in feed formulation. The current knowledge in mineral nutrition of fish is briefly reviewed.

Advancing improvement in riverine water quality caused a non-native fish species invasion and native fish fauna recovery

The knowledge of biotic and abiotic drivers that put non-native invasive fishes at a disadvantage to native ones is necessary for suppressing invasions, but the knowledge is scarce, particularly when abiotic changes are fast. In this study, we increased this knowledge by an analysis of the biomass of most harmful Prussian carp Carassius gibelio in a river reviving from biological degradation. The species' invasion followed by the invasion's reversal occurred over only two decades and were documented by frequent monitoring of fish biomass and water quality. An initial moderate improvement in water quality was an environmental filter that enabled Prussian carp's invasion but prevented the expansion of other species. A later substantial improvement stimulated native species' colonization of the river, and made one rheophil, ide Leuciscus idus, a significant Prussian carp's replacer. The redundancy analysis (RDA) of the dependence of changes in the biomass of fish species on water quality factors indicated that Prussian carp and ide responded in a significantly opposite way to changes in water quality in the river over the study period. However, the dependence of Prussian carp biomass on ide biomass, as indicated by regression analysis and analysis of species traits, suggests that the ecomorphological similarity of both species might have produced interference competition that contributed to Prussian carp's decline.

Common carp exposed to binary mixtures of Cd(II) and Zn(II): A study on metal bioaccumulation and ion-homeostasis

The aquatic environment receives a wide variety of contaminants that interact with each other, influencing their mutual toxicity. Therefore, studies of mixtures are needed to fully understand their deleterious effects on aquatic organisms. In the present experiment, we aimed to assess the effects of Cd and Zn mixtures in common carp during a one-week exposure. The used nominal waterborne metal levels were 0.02, 0.05 and 0.10 µM for Cd and 3, 7.5 and 15 µM for Zn. Our results showed on the one hand a fast Cd increase and on the other hand a delayed Zn accumulation. In the mixture scenario an inhibition of Cd accumulation due to Zn was marked in the liver but temporary in the gills. For Zn, the delayed accumulation gives an indication of the efficient homeostasis of this essential metal. Between the different mixtures, a stimulation of Zn accumulation by Cd rather than an inhibition was seen in the highest metal mixtures. However, when compared to an earlier single Zn exposure, a reduced Zn accumulation was observed. Metallothionein gene expression was quickly activated in the analysed tissues suggesting that the organism promptly responded to the stressful situation. Finally, the metal mixture did not alter tissue electrolyte levels.

Ecotoxicological effect of ketoconazole on the antioxidant system of Daphnia similis

The occurrence of emerging pharmaceutical pollutants (i.e. small drugs, antibiotics) present in aquatic environments shown to be a current environmental problem still without apparent solution. In this regard, the use of ecotoxicological techniques has been shown fundamental for the appraisal of damage to affected living organisms. Herein, ecotoxicological tests were conducted, focusing on the evaluation of the effects of ketoconazole (KTZ) on the antioxidant system of the model body Daphnia similis. In order to study the biochemical changes caused by KTZ in the antioxidant system, the enzymatic biomarkers glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX) were monitored. Toxicological tests were conducted using KTZ concentrations (0-10 μg·L^-1). Prolonged exposure to KTZ (336 h) caused changes upon the expression of antioxidant enzymes and simultaneously affected the reproductive system in those organisms. Moreover, a decrease in GST and APX activity was observed caused by KTZ exposure, respectively 79.2% (3.53 μmol min^-1 mg^-1 protein) and 24.4% (0.88 μmol min^-1 mg^-1 protein). On the other hand, it was observed an increase of 27% (0.17 μmol min^-1 mg^-1 protein) in CAT activity. Through this study, it was possible to observe the toxicological effects of KTZ, which proves its action as an oxidative stress-inducing agent and endocrine modifier in daphnids organisms.

Heavy metals affecting Neotropical freshwater fish: A review of the last 10 years of research

The expansion of urban centers, the increase in the use of chemicals in agriculture, and the significant expansion of industry has dumped increasing amounts of heavy metals into aquatic ecosystems, directly and indirectly affecting the entire food web in freshwater environments. In freshwater fish, many studies conducted worldwide have shown that these pollutants can cause alterations from the molecular level to behavioral, in all stages of life, including in future generations. Despite the great diversity of freshwater fish in the Neotropical region, few studies addressing the influence of metals on native species have been carried out. The last decade of studies showed that the effects of metals in neotropical species can be from the molecular to the behavioral level. Metals like Arsenic, Cadmium, Copper, Lead, Mercury, Chromium and Zinc have often been detected in environmental studies and evaluated in experimental approaches. Metabolically active organs showed higher levels of accumulation. In addition, some environmental studies have shown that ecologic and trophic conditions can be determinant in the level of exposure to metals. Oxidative stress, genotoxicity and several histopathological alterations were the most recurrent effects detected in target organs.

Effects of copper on an omnivorous (Astyanax altiparanae) and a carnivorous fish (Hoplias malabaricus): A comparative approach

Copper is an essential metal for life. However, in excess, it can lead to osmoregulatory disorders and oxidative stress in fish and these effects appear to be species specific. In order to evaluate the effects of copper and to compare the sensitivity of two Neotropical fishes that co-occur in nature as prey (Astyaynax altiparanae) and predator (Hoplias malabaricus), the fish were exposed to three concentrations of Cu (5 μg L^-1, 10 μg L^-1, and 20 μg L^-1) for 96 h. At the end of the experimental period, copper concentration in tissues, osmoregulatory parameters, oxidative stress biomarkers, plasma glucose, muscle glycogen and acetylcholinesterase activity were evaluated. Fish mortality (25%) was only observed for A. altiparanae exposed to Cu 20 μg L^-1. The results revealed species-specific ionic disturbances. Despite hypocalcemia, H. malabaricus showed an increase in the main gill ATPases, which probably guaranteed the maintenance of plasma Na⁺.  In A. altiparanae, there was no change in ATPase activity in the gills and hyponatremia was observed at all copper concentrations, as well as a decrease in plasma Cl^- in the Cu 20 μg L^-1 group. The strategy adopted by H. malabaricus seems to have contributed to the absence of copper accumulation in the tissues, in addition to possibly being related to the absence of oxidative stress in this species. On the other hand, there was an increase in the concentration of copper in the gills, liver, and gastrointestinal tract of A. altiparanae, as well as oxidative stress evidenced by increased lipoperoxidation in the liver and damage to erythrocytes DNA. This work reinforces the idea that copper effects are species specific and that a given concentration may not be safe for different species which can coexist in the same environment.

Single and combined acute and subchronic toxic effects of microplastics and copper in zebrafish (Danio rerio) early life stages

The evaluation of the interaction between microplastics (MPs) and heavy metals is of special importance for risk assessment. In this study, zebrafish (Danio rerio) were exposed to MPs (2 mg/L), two sub-lethal concentrations of copper (Cu, 60 and 125 μg/L) and their mixtures (Cu60 + MPs, Cu125 + MPs), from 2-h post-fertilization (hpf) until 14-days post-fertilization (dpf). Lethal and sublethal endpoints were evaluated, along with a set of biochemical and genetic biomarkers between 2 and 14 dpf. Exposure to MPs and Cu, single or combined, induced high mortality and oxidative stress in zebrafish larvae, with data showing that the antioxidant enzymes were inhibited at 6 dpf, increasing thereafter until 14 dpf, due to the accumulation of reactive oxygen species. MPs and Cu, single or combined, caused neurotoxicity in larvae by inhibiting acetylcholinesterase activity. There was an increased and significant effect of Cu + MPs groups on the evaluated biomarkers, concerning the corresponding Cu groups, suggesting that MPs may have a synergistic effect in relation to Cu. The Integrated Biomarker Response (IBR) evidenced that a higher degree of stress occurred at the larval period. Our findings highlight that MPs can act as a vector for heavy metals, therefore, influencing their bioavailability and toxicity in the organisms.

Impact of copper and zinc mixture on haematological parameters of rainbow trout (Oncorhynchus mykiss): acute exposure and recovery

Significant changes in composition of rainbow trout Oncorhynchus mykiss blood cells types were induced after 4-days exposure with mixture of Cu²⁺ and Zn²⁺ at 0.25, 0.125 and 0.06 parts of LC₅₀ in comparison to control group. The highest concentration of metal mixture (0.25 of LC₅₀) significantly induced elevation of the number of monocytes and poly-segmented neutrophils. Treatment with 0.125 parts of LC₅₀ concentration increased the number of thrombocytes, monocytes and non-segmented neutrophils. The most diluted mixture resulted in significant induction of thrombocytes, monocytes, non- and poly segmented neutrophils. Analysis of leucocyte cell types in the O. mykiss blood samples after 4-days of exposure at all applied mixture parts showed signs of monocytosis and neutrophilia. Comparison of different types of leucocytes' percentages (leukogram) in fish after 4-days exposure to metal mixture and after 4, 8, and 12-days recovery periods showed that, values of neutrophils even after the 12-days recovery period at all tested parts of LC₅₀, and monocytes after exposure with the highest (0.25) used part of LC₅₀ were not restored to control group levels. Depuration and recovery processes in treated fish are concentration and recovery period dependent.

Comparative transcriptome analyses of the liver between Xenocypris microlepis and Xenocypris davidi under low copper exposure

Copper is one of the most ubiquitous environmental pollutants worldwide. Previous studies have focused on the toxicology of high copper exposure, while there has been comparatively less research on the biological effects of low copper exposure. Low concentrations of copper often exist in freshwater ecosystems, and its impact on the fish is unclear. Both Xenocypris microlepis and Xenocypris davidi are bottom-feeding fishes widely distributed in freshwater ecosystems of China, and they are more likely to be contaminated by low concentrations of copper. Low copper exposure may have effects on molecular regulation at the level of gene expression in the two Xenocypris species. To investigate gene expression differences involved in the response to low copper concentrations between X. microlepis and X. davidi, we established the responses to low copper exposure of 0.01 mg/L for 14 days at the transcriptional level, and RNA-Seq was used to perform a comparative transcriptomic analysis of the liver. A total of 74,135 and 60,894 unigenes from X. microlepis and X. davidi were assembled by transcriptome profiling, respectively. Among these, 84 genes of X. microlepis and 165 genes of X. davidi were identified as differentially expressed genes (DEGs). There were 60 and 135 up-regulated, 24 and 30 down-regulated genes in the two species, respectively. Comparative transcriptome analyses identified five differentially co-expressed genes (DCGs) related to low copper exposure from the DEGs of the two Xenocypris species. The five DCGs were related to the fishes' growth, antioxidant system, immune system and heavy metal tolerance. The results could help us to understand the molecular mechanisms of the response to low copper exposure, and the data should provide a valuable transcriptomic resource for the genus Xenocypris.

Toxic effects of dietary copper and EGCG on bioaccumulation, antioxidant enzyme and immune response of Korean bullhead, Pseudobagrus fulvidraco

There are few reports of dietary Cu (copper) toxicity to Korean bullhead, Pseudobagrus fulvidraco, and little is known about recovery from dietary Cu exposure. In this study, P. fulvidraco (mean length 16.9 ± 1.38 cm, and mean weight 53.2 ± 1.22 g) were exposed for 4 weeks to dietary Cu concentration of 0 (control), 700, 900, and 1100 mg Cu kg^-1 dry feed to establish maximum tolerable levels of dietary Cu. All fish were then fed the dietary EGCG (Epigallocatechin gallate) concentration of 100 and 500 mg EGCG kg^-1 dry feed for a further 2 weeks to assess recovery. We were measured bioaccumulation (in the intestine, liver, and gill tissue), antioxidant enzymes (SOD and CAT) and immune responses (lysozyme and phagocytosis). The Cu exposure induced a significant accumulation in the intestine, liver, and gill tissues and the highest accumulation was observed in intestinal tissues (17-34 fold), but dietary EGCG exposure decreased (about 0.8-fold) Cu concentration in each tissue (ANOVA, P < 0.05). In antioxidant enzymes, SOD and CAT significantly increased by approximately 1.6-fold by dietary Cu exposure in the liver and gill tissue, respectively, but dietary EGCG exposure decreased SOD and CAT by about 1.1-fold, respectively (ANOVA, P < 0.05). For immune responses, lysozyme and phagocytosis in the blood significantly were decreased by approximately 1.5-fold, respectively, by dietary Cu exposure, but dietary EGCG exposure increased lysozyme and phagocytosis by about 1.1-fold, respectively (ANOVA, P < 0.05). During recovery period, bioaccumulation, antioxidant enzymes (SOD and CAT activity), and immune response (lysozyme and phagocytosis activity) tended to alleviate the significant changes by Cu exposure, and the tendency to return normal state was observed in high level of EGCG. The result of this study indicate that Cu exposure to P. fulvidraco affects bioaccumulation, antioxidant enzymes, and immune responses, and high level of EGCG were effective to alleviate the toxic effects of Cu exposure.

Manganese dioxide nanosheets induce mitochondrial toxicity in fish gill epithelial cells

The development and production of engineered 2D nanomaterials are expanding exponentially, increasing the risk of their release into the aquatic environment. A recent study showed 2D MnO2 nanosheets, under development for energy and biomedical applications, dissolve upon interaction with biological reducing agents, resulting in depletion of intracellular glutathione levels within fish gill cells. However, little is known concerning their toxicity and interactions with subcellular organelles. To address this gap, we examined cellular uptake, cytotoxicity and mitochondrial effects of 2D MnO2 nanosheets using an in vitro fish gill cell line to represent a target tissue of rainbow trout, a freshwater indicator species. The data demonstrate cellular uptake of MnO2 nanosheets into lysosomes and potential mechanisms of dissolution within the lysosomal compartment. MnO2 nanosheets induced severe mitochondrial dysfunction at sub-cytotoxic doses. Quantitative, single cell fluorescent imaging revealed mitochondrial fission and impaired mitochondrial membrane potential following MnO2 nanosheet exposure. Seahorse analyses for cellular respiration revealed that MnO2 nanosheets inhibited basal respiration, maximal respiration and the spare respiratory capacity of gill cells, indicating mitochondrial dysfunction and reduced cellular respiratory activity. MnO2 nanosheet exposure also inhibited ATP production, further supporting the suppression of mitochondrial function and cellular respiration. Together, these observations indicate that 2D MnO2 nanosheets impair the ability of gill cells to respond to energy demands or prolonged stress. Finally, our data demonstrate significant differences in the toxicity of the 2D MnO2 nanosheets and their microparticle counterparts. This exemplifies the importance of considering the unique physical characteristics of 2D nanomaterials when conducting safety assessments.

Differences in the subcellular distribution of cadmium and copper in the gills and liver of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss)

Recent studies have shown that white sturgeon (Acipenser transmontanus) are more resistant to cadmium (Cd) compared to rainbow trout (Oncorhynchus mykiss), whereas they are more sensitive than rainbow trout when exposed to copper (Cu). Differences in the subcellular distribution of metals among species could be one of the factors responsible for the differences in the sensitivity to metals. Although, subcellular distribution has been studied extensively in many species with many metals, its direct role in species-specific differences in the sensitivity has not been well studied. The objective of this study was to evaluate the role of subcellular distribution of metals in species-specific differences in the sensitivity to metals between sturgeon and trout. We compared the subcellular distribution of metals Cd and Cu in the cellular debris, heat-stable proteins, heat-denatured fraction, metal-rich granules, and organelles fractions from the gills and liver after exposure of juveniles of both species to 1.25 and 20 μg/L Cd and Cu for 8 days, respectively. Sturgeon diverted a higher amount of Cd towards biologically inactive metal pool (BIM) and a lower amount towards the biologically active metal pool (BAM) compared to trout in both tissues. This explained why sturgeon are able to tolerate a relatively higher exposure level to Cd compared to trout. For Cu, there was no statistically significant species-specific differences in the amounts diverted towards either BAM or BIM; hence, white sturgeon's greater sensitivity to Cu was not explained by its subcellular distribution strategies.

Effects of cypermethrin on the hepatic transcriptome and proteome of the red claw crayfish Cherax quadricarinatus

Cypermethrin (CYP) is a synthetic pyrethroid broadly used for pest control, however, it is extremely toxic to aquatic organisms. To assess the toxicity of CYP in red claw crayfish Cherax quadricarinatus, transcriptional and proteomic approaches combining two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry were used to compare the hepatic expression profiles. A total of 41,349 unigenes and 8839 differentially expressed genes (DEGs) were obtained, which were enriched in the process. The category of 779 (0.625 ng L^-1 CYP vs Con), 1963 (1.25 vs Con), and 2066 (1.25 vs 0.625) DEGs were screened. All findings suggested that CYP can induce antioxidant and biotransformation modulation variations in C. quadricarinatus to resist immunotoxicity and oxidative damages. The category of 196 (0.625 ng L^-1 CYP vs Con) specific proteins were differentially expressed: 24 proteins were upregulated, and 20 proteins were downregulated relative to CYP. Protein identification indicated the KEGG pathways of the human immunodeficiency virus 1 infection, insulin signaling pathway, and influenza A enriched. From the differential expression of the selected nine proteins, the increased Loc113824800, Rps19, Atp2, Rps10, Hsp40, Brafldraft_124327, and the decreased Loc117331934, Loc113213835, and Loc106806551 revealed. While for the verification of the eight genes in transcriptome and the above nine genes in proteomic, specifically, gpx5, ggt, loc106458463, chelonianin decreased in the 0.625 ng L^-1 CYP group. The transcripts of loc113816050, akr1d1 and gst, chelonianin and loc108675455 decreased and increased in the 1.25 ng L^-1 CYP group, respectively. The present study reflects the overall change in cellular structure and metabolism related to the resistance of pyrethroid insecticides.

Alleviative effects of dietary microbial floc on copper-induced inflammation, oxidative stress, intestinal apoptosis and barrier dysfunction in Rhynchocypris lagowski Dybowski

The heavy metal poisoning in humans and fish represents a significant global problem. Copper (Cu), as an essential micronutrient in human and animal metabolism, often accumulates excessively in aquatic environment. The microbial floc is rich in a variety of probiotics and bioactive compounds, which has been documented to have the functions of antioxidant and immunoenhancement. A 64-day experiment was conducted to investigate the protective effects and potential mechanisms of dietary supplementation of microbial floc and Cu exposure on inflammatory response, oxidative stress, intestinal apoptosis and barrier dysfunction in Rhynchocypris lagowski Dybowski. A total of four hundred fifty R. lagowski were fed five experimental diets containing graded levels of microbial floc from 0% to 16% (referred to as B0, B4, B8, B12 and B16, respectively) in the first 60 days, and 96 h of acute copper exposure test was carried out in the last four days. The results showed that microbial floc exerted significant alleviative effects by preventing alterations in the levels of bioaccumulation, caspase3, caspase8, caspase9, malondialdehyde and interleukin-6, improving the activities of lysozyme, complement C3, complement C4, immunoglobulin M, alkaline phosphatase, heat shock protein 70, heat shock protein 90 and glutathione peroxidase, catalase, superoxide dismutase, total antioxidant capacity. In addition, microbial floc assisted in regulating the expression of NF-κB/Nrf2 signaling molecule genes, including NF-κB, TNF-α, IL-1β, IL-8, IL-10, TGF-β, Keap1, Nrf2, Maf, HO-1, CAT, CuZn-SOD, GCLC and GPX. Overall, our results suggest that dietary supplementation with of microbial floc can alleviate copper-induced inflammation, oxidative stress, intestinal apoptosis and barrier dysfunction in R. lagowski. A suitable supplementation level of approximately 12% microbial floc is recommended in the present study.

Antagonistic bioaccumulation of waterborne Cu(II) and Cd(II) in common carp (Cyprinus carpio) and effects on ion-homeostasis and defensive mechanisms

In the aquatic environment, metals are present as mixtures, therefore studies on mixture toxicity are crucial to thoroughly understand their toxic effects on aquatic organisms. Common carp (Cyprinus carpio) were used to assess the effects of short-term Cu(II) and Cd(II) mixtures, using a fixed concentration of one of the metals, representing 25 % of its individual 96h-LC₅₀ (concentration lethal for 50 % of the population) combined with a variable concentration of the other metal corresponding to 10, 25 or 50 % of its 96h-LC₅₀, and vice versa. Our results showed a fast Cu and Cd bioaccumulation, with the percentage of increase in the order gill > liver > carcass. An inhibitory effect of Cu on Cd uptake was observed; higher Cu concentrations at fixed Cd levels resulted in a decreased accumulation of Cd. The presence of the two metal ions resulted in losses of total Na, K and Ca. Fish tried to compensate for the Na loss through the induction of the genes coding for Na⁺/K⁺-ATPase and H⁺-ATPase. Additionally, a counterintuitive induction of the gene encoding the high affinity copper transporter (CTR1) occurred, while a downregulation was expected to prevent further metal ion uptake. An induction of defensive mechanisms, both metal ion binding protein and anti-oxidant defences, was observed. Despite the metal accumulation and electrolyte loss, the low mortality suggest that common carp is able to cope with these metal levels, at least during a one-week exposure.

Comparative effects of Cu (60-80 nm) and CuO (40 nm) nanoparticles in Artemia salina: Accumulation, elimination and oxidative stress

In this study, nanotoxicity tests were made by exposure of Artemia salina to copper (Cu 60-80 nm) and copper oxide (CuO 40 nm) nanoparticles (NPs) at different concentrations (0.2, 1, 5, 10, 25, and 50 mg/l) during some exposure duration. Characterization of Cu and CuO NPs were performed using Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS), Zeta Potential, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transformation Infrared (FT-IR) analyzes. In organisms, the accumulation and elimination rates of NPs was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis and the oxidative stress effects on A. salina were determined by Glutathione (GSH) and Thiobarbituric acid reactive substances (TBARS) analysis methods. Both NPs were found to differ in accumulation and elimination rates at each application time and in parallel with the increase in concentration. In each group, it was determined that ion release increased with application time. The results showed that the accumulation rates in Cu NPs had a tendency to increase at 48 h and to decrease at 72 h in concentrations of 0, 2 and 1 mg/l, respectively. And in the all other concentrations have been seen an increasing trend within the time. In the CuO NPs (40 nm), accumulation rates were a decrease trend at 48th hour and an increase trend at 72nd hour except 10 mg/l concentration. In the 10 mg/l group was an increase trend with the application period. Cu NP, TBARS value increased with increasing concentrations and the highest increase was observed at 24 h of 5 ppm group. The groups showed a tendency to increase-decrease-increase-decrease in TBARS levels in terms of elapsed time (24th, 48th, 72nd hour and elimination) (5 ppm and 10 ppm groups tended to decrease in TBARS level at 72nd hour). TBARS increased with increasing concentration ratios in CuO NPs (40 nm).

Effects of dietary Cu and Zn on the accumulation, oxidative stress and the expressions of immune-related genes in the livers of Nile tilapia (Oreochromis niloticus)

Excess Cu and Zn can cause many adverse effects in fish. However, few studies have addressed the effects of dietary Cu and Zn on antioxidant physiology and immunity and the underlying mechanisms in fishes. In this study, accumulation of Cu and Zn, effects on the antioxidant enzymes and the transcriptional expressions of immune-related genes were examined in the Oreochromis niloticus fed the Cu and/or Zn enriched duckweed. The results showed that the liver and intestine had the highest accumulation of Cu²⁺ and Zn²⁺ while the muscle had the lowest accumulation of these two metals. The activities of SOD, CAT, GPx and the contents of GSH, GSSG in the liver of all treatment groups were significantly decreased compared to the control group. MDA content was significantly elevated in all treatment groups after feeding for 21 days, implying lipid peroxidation in the liver. In the Cu + Zn group, the activities of SOD, GPx and the GSSG content in the liver were significantly decreased. Compared with the Zn group, the LZM activity in the Cu + Zn group was reversed after feeding for 42 days (P < 0.05). The transcriptional expressions of immune-related genes (TNF-α, INF-γ and IL-1β) in Cu, Zn, Cu + Zn groups were significantly inhibited compared with the control group after treatment for 21 days. Compared with the Cu + Zn group, the level of INF-γ transcripts was significantly reduced in the Cu and Zn group, while the TNF-α expression was elevated after treatment for 42 days. Cu and Zn had synergistic effects on the antioxidant system. Cu has greater effects than Zn on the immunity of O. niloticus. This study demonstrates that dietary Cu and Zn may pose a potential threat to the tilapia populations.

Comparative analyses of oxidative stress response and metallothionein induction in white sturgeon and rainbow trout during acute waterborne copper exposure

Early life-stages of the endangered white sturgeon (Acipenser transmontanus) have been shown to be among the most sensitive fishes to aqueous copper (Cu) exposure. In a recent analogous study, we examined the role of whole-body Cu accumulation and Na homeostasis in species-specific differences between the sensitivity of white sturgeon and a common laboratory fish model, rainbow trout, to Cu. However, the potential roles of important mechanisms such as Cu-induced oxidative stress and/or metallothionein (MT) induction as potential drivers of sensitivity of white sturgeon to Cu have not been investigated to date. Here, rainbow trout and white sturgeon from three different early life-stages were exposed to waterborne Cu for 96 h, following which major antioxidant parameters, lipid peroxidation and MT gene expression were evaluated. Results indicated that during larval and swim-up life-stages, Cu induced oxidative damage in white sturgeon was greater than in rainbow trout. Moreover, baseline glutathione (GSH) was significantly greater in rainbow trout than white sturgeon. Observations also suggested that trout exceedingly relied on GSH to combat Cu-induced oxidative stress as they grew older. In contrast, sturgeon recruited an increasing level of MT to neutralize Cu-induced oxidative stress and/or Cu loading. In our recent study, we demonstrated that Na homeostasis is more susceptible to Cu in white sturgeon than in rainbow trout. Collectively, these findings indicate that the greater degree of oxidative damage in early life-stages, in addition to the higher magnitude of the disruption of Na homeostasis, contributes to the higher sensitivity of white sturgeon to Cu exposure.

Chemical and Colloidal Dynamics of MnO2 Nanosheets in Biological Media Relevant for Nanosafety Assessment

Many layered crystal phases can be exfoliated or assembled into ultrathin 2D nanosheets with novel properties not achievable by particulate or fibrous nanoforms. Among these 2D materials are manganese dioxide (MnO2 ) nanosheets, which have applications in batteries, catalysts, and biomedical probes. A novel feature of MnO2 is its sensitivity to chemical reduction leading to dissolution and Mn2+ release. Biodissolution is critical for nanosafety assessment of 2D materials, but the timing and location of MnO2 biodissolution in environmental or occupational exposure scenarios are poorly understood. This work investigates the chemical and colloidal dynamics of MnO2 nanosheets in biological media for environmental and human health risk assessment. MnO2 nanosheets are insoluble in most aqueous phases, but react with strong and weak reducing agents in biological fluid environments. In vitro, reductive dissolution can be slow enough in cell culture media for MnO2 internalization by cells in the form of intact nanosheets, which localize in vacuoles, react to deplete intracellular glutathione, and induce cytotoxicity that is likely mediated by intracellular Mn2+ release. The results are used to classify MnO2 nanosheets within a new hazard screening framework for 2D materials, and the implications of MnO2 transformations for nanotoxicity testing and nanosafety assessment are discussed.

Toxicity and bioaccumulation of Cadmium, Copper and Zinc in a direct comparison at equitoxic concentrations in common carp (Cyprinus carpio) juveniles

The individual toxicity and bioaccumulation of cadmium, copper and zinc for common carp juveniles was evaluated in a direct comparison in two experimental setups. First, fish were exposed for 10 days to different metal concentrations in order to link metal bioaccumulation to LC₅₀ values (concentration lethal to 50% of the animals) and incipient lethal levels (ILL, concentration where 50% survives indefinitely). Accumulated metals showed a positive dose dependent uptake for cadmium and copper, but not for zinc. Toxicity was in the order cadmium>copper>zinc with 96h LC₅₀ values for cadmium at 0.20±0.16 μM, for copper at 0.77±0.03 μM, and for zinc at 29.89±9.03 μM respectively. For copper, the 96h exposure was sufficient to calculate the incipient lethal level and therefore 96h LC₅₀ and ILL levels were the same, while for cadmium and zinc 5 to 6 days were needed to reach ILL resulting in slightly lower values at 0.16 μM and 28.33 μM respectively. Subsequently, a subacute exposure experiment was conducted, where carp juveniles were exposed to 2 equitoxic concentrations (10% and 50% of LC₅₀ 96 h) of the three metals for 1, 3 and 7 days. Again a significant dose-dependent increase in gill cadmium and copper, but not in zinc, was observed during the 7-day exposure. Copper clearly affected sodium levels in gill tissue, while zinc and cadmium did not significantly alter any of the gill electrolytes. The overall histopathological effects (e.g. hyperemia and hypertrophy) of the metal exposures were mild for most of the alterations. Our study showed that copper an cadmium (but not zinc) showed dose dependent metal accumulation, however this bioaccumulation was only correlated with mortality for cadmium. Metal specific alterations were reduced gill sodium levels in copper exposed fish and oedema of the primary epithelium which typically occurred in both levels of zinc exposure.

Bioflocs protects copper-induced inflammatory response and oxidative stress in Rhynchocypris lagowski Dybowski through inhibiting NF-κB and Nrf2 signaling pathways

Copper (Cu) is an essential element in the metabolic process of humans and animals, but it can cause toxicity at high concentrations of exposure. Bioflocs has been proved to have antioxidant, immune-enhancing and anti-inflammatory properties. Here, the purpose of this study was to evaluate potential mechanisms and protective effects of bioflocs and Cu exposure on inflammatory response, oxidative stress and immune-related genes and protein expression in Rhynchocypris lagowski Dybowski. 360 healthy R. lagowski were irregularly distributed among 12 tanks (3 tanks per group, 30 fish per tank). The experiment was divided into two parts: the feeding experiment was carried out in the first eight weeks, followed by acute copper exposure for 96 h. Then we selected the stressed fish for experimental analysis. The results provided evidences that bioflocs protected the R. lagowski by inhibiting the accumulation of copper, the activity of immune enzymes and the expression of NF-κB signaling pathway related genes and proteins, and the activity of antioxidant enzymes and the expression of Nrf2 signaling pathway related genes. Overall, these findings suggest that bioflocs could regulate the activation of Nrf2 and protect acute copper exposure induced inflammatory response by inhibiting the NF-κB signaling pathway in R. lagowski.

Interactive effect of thermal and hypoxia on largemouth bass (Micropterus salmoides) gill and liver: Aggravation of oxidative stress, inhibition of immunity and promotion of cell apoptosis

High temperatures and low oxygen in aquatic environments, such as intensive aquaculture or in natural watersheds, inevitably cause stress in fish. Fish are exposed to high temperatures during the summer, which exacerbates hypoxia. Hypoxia (1.2 ± 0.2 mg/L) under 20 °C (20 HG) and 26 °C (26 HG) was simulated to induce stress in largemouth bass (Micropterus salmoides). Related enzymes and genes involved in antioxidant, immune, and apoptotic responses were selected to explore the interactive effects of temperature and hypoxia on largemouth bass. The results showed that malondialdehyde (MDA) levels in plasma, gill, and liver increased in the 26 HG (p < 0.05). Liver superoxide dismutase (SOD) activity increased in the 26 HG. Peak SOD (SOD1, SOD2, SOD3a, and SOD3b), CAT, and GSH-Px mRNA levels in the gill and liver were observed at 12-24 h of stress. The levels of gill and liver total antioxidant capacity, catalase (CAT), glutathione peroxidase (GSH-Px) activities and other enzyme activities and genes in the 26 HG were higher than those in the 20 HG (p < 0.05). The gill and liver acid phosphatase and alkaline phosphatase activities increased with time in the 26 HG (p < 0.05), while gill and liver lysozyme activities in the 26 HG were lower than those in the 20 HG (p < 0.05). Tumor necrosis factor-α mRNA level was upregulated in the gill and downregulated in the liver at 24 h in the 26 HG. Interleukin (IL)-1β and IL-8 mRNA levels were upregulated in the gill and liver in the 26 HG at 24 h, whereas IL-15 mRNA level was downregulated in the 26 HG at 12 h. Transforming growth factor-β1 mRNA level was upregulated in the gill in the 20 HG at 24 h, but downregulated in gill and liver in the 26 HG at 24 h. Similarly, IL-10, Hepcidin-1, and Hepcidin-2 showed lower expression levels in the 26 HG. Gill and liver caspase-3 activities were higher in the 26 HG (p < 0.05), and gill caspase-3 activity was higher than that in the liver. The mRNA levels of proapoptotic genes (caspase-3, caspase-8, and caspase-9) were higher in the 26 HG. The present study demonstrates the interactive effects of temperature and hypoxia on stress in largemouth bass gill and liver. These results will be helpful to understand the mechanisms of stress induced by temperature and hypoxia in fish and provide a theoretical basis for aquaculture management.

Assessment of Oxidative Stress on Artemia salina and Daphnia magna After Exposure to Zn and ZnO Nanoparticles

In this study, the effect of zinc nanoparticles (Zn NPs) and zinc oxide nanoparticles (ZnO NPs) on Artemia salina and Daphnia magna, the primary consumer organisms were investigated. In this sense, investigation of trophic transfer and ecological sustainability potentials among living things, such as fish and crustaceans that are at the top of the food chain were also aimed. Zn NPs in the size of 40-60 nm and 80-100 nm and ZnO NPs (10-30 nm) were administered to A. salina and D. manga (respectively in total 105000 and 14000 individuals) in seven groups (Control, 0.2, 1, 5, 10, 25 ve 50 ppm) with three repetitions for a period of 72 h. Intensive and possible misuse of nanoscale materials is one of the biggest threats to the environment and all living things worldwide. Therefore, the control mechanisms for the use of NPs need to be established.

Microplastics and copper effects on the neotropical teleost Prochilodus lineatus: Is there any interaction?

Microplastics (MP) are emerging contaminants widely found in aquatic ecosystems. In addition to MP toxicity itself, there is increasing concern about the MP adsorption capacity and the interactive effects with other contaminants, such as copper. The objective of this research was to investigate the effects of polyethylene microplastic and its association with copper (Cu) in genotoxic, biochemical, and physiological biomarkers of the neotropical teleost Prochilodus lineatus. Fish were exposed for 24 and 96 h to MP (20 μg L^-1) and Cu (10 μg L^-1) and MP + Cu. The results showed that MP and Cu, both isolated and in combination, promoted DNA damage in erythrocytes (96 h) and liver cells (24 and 96 h) indicating that MP and Cu are genotoxic. Fish exposed only to Cu (96 h) showed a decrease in lipid peroxidation in the liver despite of the decrease in glutathione content, indicating the efficiency of other antioxidant defenses. Brain acetylcholinesterase was inhibited in the animals from all the treatments. Although MP did not influence on Cu accumulation in tissues, decreased plasma Na⁺ and Ca²⁺ (24 h) occurred after the exposure to MP and Cu, isolated and combined. Exposure to MP and MP + Cu resulted in decreased activity of Ca²⁺-ATPase (24 h). Taken altogether, these results showed that MP and Cu depicted genotoxic, neurotoxic, and physiological effects on P. lineatus, both alone and combined. An interaction between Cu and MP was observed in plasma Ca²⁺, where the combination of both contaminants caused a greater effect than the contaminants alone.

Studies of the mechanism of fatty liver formation in Takifugu fasciatus following copper exposure

Fatty liver is widely observed during Takifugu fasciatus production, but the mechanisms underlying fatty liver formation remain unknown. The present study was conducted to determine the potential effects of copper (Cu) on hepatic lipid deposition and metabolism in T. fasciatus after 21 days of exposure to Cu (levels: 0, 20 and 100 μg/L). Copper exposure decreased the weight gain rate (WG) in T. fasciatus, but increased the values of the viscerosomatic index (VSI) and hepatosomatic index (HSI) compared with the control. The time-dependent Cu accumulation in tissues increased as the Cu concentration increased. The order of Cu accumulation was liver > intestine > muscle. The lipid content, triglyceride (TG) content and lipoprotein lipase (LPL) activity increased after Cu exposure compared with the control. In addition, more lipid droplets and greater vacuolization were observed in the liver after exposure to 20 μg/L Cu than after 100 μg/L Cu. The expression of genes involved in lipogenesis (g6pd, 6pgd, lpl, fas and acc), lipolysis (hsl and cpt 1) and transcription (ppar α and ppar ^©) was dependent on Cu. An analysis of the intestinal microbiome community showed that the highest values of the Chao 1 index, ACE, Shannon index and Simpson index were obtained in fish exposed to 20 μg/L Cu, whereas the lowest values were obtained after the 100 μg/L Cu treatment. The Principal Coordinates Analysis (PCoA) plots of the data revealed structural differences in the groups treated with Cu compared with the control group. At the phylum level, the intestinal microbiota in the Cu-treated and control fish were dominated by Proteobacteria and Bacteroidetes. The higher Firmicutes to Bacteroidetes ratio was observed in fish treated with 20 μg/L Cu compared with other groups, while the lowest ratio was observed in fish exposed to 100 μg/L Cu. Our study revealed the mechanisms by which Cu exposure altered (i) lipid deposition in the body and (ii) the intestinal microbiome, which may contribute to maintain the health status of T. fasciatus for the aquaculture.

Sensitivity of white sturgeon and rainbow trout to waterborne copper exposure: A comparative study of copper-induced disruption of sodium homeostasis

Recent studies have demonstrated that white sturgeon are more sensitive to acute exposure to Cu than rainbow trout (Oncorhynchus mykiss), especially during early life-stages. However, the physiological mechanisms underlying this difference in sensitivity to Cu is not known. In the present study, we first confirmed the higher sensitivity (lower 96 h LC₅₀ values) of white sturgeon to Cu at three different life stages (larva, swim-up, and juvenile) relative to their counterparts in rainbow trout. We also demonstrated that acute exposure to Cu (50 μg/L for 4.5 h) caused a significantly greater reduction in the rate of waterborne Na uptake in white sturgeon relative to that in rainbow trout across all three life-stages. In agreement with this observation, we also found that acute exposure to Cu (20 μg/L for 48 h) elicits a significantly greater decrease in whole body Na level in all life stages of white sturgeon compared to rainbow trout. In contrast, white sturgeon demonstrated a higher or similar level of Cu body burden relative to rainbow trout during acute Cu exposure (20 μg/L for 24 h), thereby indicating that Cu bioaccumulation is not a good indicator of its toxicity in these species. Overall, our study demonstrated that the differences in sensitivity to acute Cu exposure between white sturgeon and rainbow trout can be explained on the basis of differential effects of Cu on Na homeostasis.

Single and combined exposures of waterborne Cu and Cd induced oxidative stress responses and tissue injury in female rare minnow (Gobiocypris rarus)

Copper (Cu) and cadmium (Cd) are two kinds of abundant toxic metals in aquatic ecosystem. The present study evaluated the effects of waterborne Cu and Cd on oxidative stress responses and histological alterations in female rare minnow (Gobiocypris rarus). Fish were exposed for 7 days to: (i) control (no added Cu or Cd), (ii) waterborne Cu (39.2 μg L^-1), (iii) waterborne Cd (299.6 μg L^-1), and (iv) Cu and Cd in mixture (19.6 and 149.8 μg L^-1, respectively). Antioxidant enzyme activities and gene mRNA abundance in fish tissues (gills, liver, and ovaries) were induced by Cu and Cd exposures, both individually and in mixture, at day 1, but an asynchronous response was observed between most enzyme activities and gene mRNA abundance following 7 days exposure. Biochemical analysis and histological observation indicated that exposure to Cu and Cd, alone and in combination, caused evident damage to lipids and tissue structure in gills, liver and ovaries. Comparing with single Cu or Cd exposure, Cu and Cd co-exposure induced greater increase in the mRNA expression of most antioxidant genes and caused more severe lesions in fish tissues, which suggested that exposure to waterborne Cu and Cd in mixture might increase their individual toxicity. Furthermore, positive relationships between nuclear factor erythroid 2-related factor (Nrf2) expression and expression of manganese superoxide dismutase (Mn-SOD) and catalase (CAT) were also observed in the present study, which suggested that Cu or/and Cd induced expression of these antioxidant genes were might through activation of Nrf2.

Species and life-stage specific differences in cadmium accumulation and cadmium induced oxidative stress, metallothionein and heat shock protein responses in white sturgeon and rainbow trout

Understanding the mechanistic basis of differences in the sensitivity of fishes to metals is important for developing informed ecological risk assessment approaches for metals. Whole body metal accumulation, metallothionein induction, oxidative stress and associated antioxidant response, as well as heat shock proteins (mainly HSP70) are known to play important roles in determining the toxicity of metals in fish. Hence, in this study we have cross-evaluated these parameters as a function of Cd exposure across different life-stages of two evolutionarily distinct fish species, namely rainbow (Oncorhynchus mykiss) trout and white sturgeon (Acipenser transmontanus). These two species have been shown to differ significantly in their physiological and apical responses to Cd exposure. The findings of the present study suggest that species-specific differences in the sensitivity to Cd could partially be explained by HSP70 gene response and oxidative damage biomarkers. However, not all the parameters studied in this study could explain the life-stage specific differences universally and were limited to only some life-stages. Based on the observations in the present study and other recent studies, it is apparent that species- and life-stage specific differences in the sensitivity to Cd and possibly other metals is a complex phenomenon and could be driven by multiple toxicokinetic and toxicodynamic factors.

Trace Metals in the Freshwater Fish Cyprinus carpio: Effect to Serum Biochemistry and Oxidative Status Markers

Interactions between trace metals, serum biochemical parameters, and oxidative status markers were observed. Freshwater fish Cyprinuscarpio blood samples (n = 38) were collected at the beginning of May (n = 19) and at the end of July (n = 19) of 2015. The concentrations of metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sr, and Zn) were analyzed in blood serum samples of fishes by inductively coupled plasma optical emission spectrometry (ICP-OES), and Hg was determined by cold-vapor atomic absorption spectroscopy (CV-AAS). The general scheme of descending concentrations of metals in blood serum samples was as follows: Zn > Fe > Cu > Sr > Cr > Ni > Mn > Pb > Se > As > Cd > Hg. Zn was the most accumulated element (4.42-119.64 mg/L) in both seasons. Overall, the trace element content was higher in spring season, except Hg, Ni, Se, and Sr. The seasonal effect was confirmed for Mn, Zn, Mg, Glu, AST, and Chol levels and for most oxidative status markers. The gender effect was confirmed for Sr, GPx, PC, Chol, and CK concentrations. Trace metals (especially Cd, Cr, Cu, Fe, Hg, Mn, Ni, Sr, Zn, As) significantly affected some blood serum chemistry parameters. The correlation analysis between oxidative status markers (ROS, TAC, MDA, SOD, GSH, UA, BHB, and Alb) and trace metal (Cd, Cu, Ni, Sr, Hg, Pb, Fe, Mn) content confirmed statistically significant interactions in both seasons. Obtained results indicate specific actions of trace metals.

Limited oxidative stress in common carp (Cyprinus carpio, L., 1758) exposed to a sublethal tertiary (Cu, Cd and Zn) metal mixture

Analyzing effects of metal mixtures is important to obtain a realistic understanding of the impact of mixed stress in natural ecosystems. The impact of a one-week exposure to a sublethal metal mixture containing copper (4.8 μg/L), cadmium (2.9 μg/L) and zinc (206.8 μg/L) was evaluated in the common carp (Cyprinus carpio). To explore whether this exposure induced oxidative stress or whether defense mechanisms were sufficiently fitting to prevent oxidative stress, indicators of apoptosis (expression of caspase 9 [CASP] gene) and of oxidative stress (malondialdehyde [MDA] level and xanthine oxidase [XO] activity) were measured in liver and gills, as well as activities and gene expression of enzymes involved in antioxidant defense (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], glutathione reductase [GR] and glutathione-S-transferase [GST]). The total antioxidative capacity (T-AOC) was also quantified. No proof of oxidative stress was found in either tissue but there was indication of apoptosis in the liver. CAT, GPx, GR and GST total activities were reduced after 7 days, suggesting a potential decrease of glutathione levels and risk of increased free radicals if the exposure would have lasted longer. There were no major changes in the total activities of antioxidant enzymes in the gills, but the relative expression of the genes coding for CAT and GR were triggered, suggesting a response at the transcription level. These results indicate that C. carpio is well equipped to handle these levels of metal pollution, at least during short term exposure.

Genome-wide identification and expression of the entire 52 glutathione S-transferase (GST) subfamily genes in the Cu2+-exposed marine copepods Tigriopus japonicus and Paracyclopina nana

In this study, the entire glutathione S-transferases (GSTs), the major phase II detoxification enzyme, were identified in two marine copepod species Tigriopus japonicus and Paracyclopina nana. The genome-wide identification of GSTs in T. japonicus and P. nana resulted in 32 and 20 GSTs in total, respectively. Among the identified GSTs, two specific classes of GSTs, specifically sigma and delta/epsilon GSTs were the dominant form of cytosolic GSTs in T. japonicus, while delta/epsilon and mu classes were dominant cytosolic GSTs in P. nana. In addition, Membrane-Associated Proteins in Eicosanoid and Glutathione metabolism (MAPEG) family were found in relatively higher proportion compared to other classes. Moreover, sigma, delta/epsilon, and microsomal GSTs have shown to expand through tandem duplication. To validate the detoxification function of the identified GSTs, both copepods were exposed to copper (Cu²⁺) and the reactive oxygen species (ROS) level and GST activity were measured. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in two marine copepod species and their important role in marine environmental ecotoxicology.

Evaluation of Single and Joint Toxicity of Perfluorinated Carboxylic Acids and Copper to Metal-Resistant Arthrobacter Strains

Perfluorocarboxylic acid compounds (PFCAs) and copper have been regarded as ubiquitous environmental contaminants in aquatic ecosystems worldwide. However, data on their possible joint toxic effects on microorganisms are still lacking. To study the combined effects of four PFCAs with different carbon chain lengths and copper, a series of experiments were conducted to explore the acute toxicity of these PFCAs in the absence and presence of copper on a metal-resistant Arthrobacter strain GQ-9 by microcalorimetry. The thermokinetic parameters, including growth rate constant (k), inhibitory ratio (I), and half inhibitory concentration (IC₅₀), were calculated and compared using the data obtained from the power-time curves. Our work revealed that GQ-9 is more resistant to perfluorooctanoic acid (PFOA) than Escherichia coli. The single and joint toxicity of PFCAs with copper are dose- and carbon chain length-dependent. The longer the carbon chain length of PFCAs, the higher the toxicity. In addition, PFCAs interacted synergistically with copper. This work could provide useful information for the risk assessment of co-exposure to perfluorinated compounds and heavy metals in natural environments.