Effects of chronic waterborne cadmium and zinc interactions on tissue-specific metal accumulation and reproduction in fathead minnow (Pimephales promelas)

Growth increase and gonadal dysfunction of the lined seahorse triggered by zinc exposure

Seahorses are characterized by unique characteristics such as a male pregnancy reproductive strategy and grasping preferences, which make these species vulnerable to various environmental risks. Zinc (Zn) is one of the most frequently occurring toxic elements in coastal waters; however, little is known about the effect of Zn exposure on seahorses. In the present study, line seahorses (Hippocampus erectus) were exposed to waterborne Zn (0.2 and 1.0 mg/L) and the impact on growth and gonadal development was investigated. Zn exposure induced growth improvement, but also led to gonadal dysfunction in the lined seahorse. Female seahorses exhibited high testosterone levels, immature follicles, and weight increase after Zn exposure, which is the typical characteristics of a polycystic ovary syndrome (PCOS)-like phenotype. Transcriptomic data suggested that the Zn-induced growth promotion resulted from the dysregulated expression of fat accumulation genes. Further investigation of gene expression profiles in the brain, ovaries, and testes indicated that Zn affected the expression of genes involved in growth, immunity, tissue remodeling, and gonadal development by regulating serum steroid hormone levels and androgen receptor expression. This study not only clarifies the complex impact of Zn on seahorses using physiological, histological, and molecular evidence but can also provide new insights into the mechanism underlying PCOS in reproductive-aged women. Moreover, this work demonstrates the risk of the common practice of Zn supplementation in the aquaculture industry as the consequent growth yield may not represent a healthy condition.

Zinc modulates hypothalamo-pituitary-gonadal-liver axis to impair reproduction in female Mystus vittatus (Bloch, 1794)

The present study investigated the effects of zinc on the hypothalamo-pituitary-gonadal-liver (HPGL) axis of the bagrid catfish Mystus vittatus. Female fish (pre-ovulatory and ovulatory phases) were exposed to zinc sulphate at 1/10th of LC50 (5.62 mg/L) for 60 days and sacrificed at every 15-day interval to collect tissues. Zinc concentration in all tissues was significantly higher in the metal-exposed group at all exposure durations compared to control for both phases. Metallothionein (MT) levels increased in the brain, liver and ovary of fish from both phases with exposure duration. Reactive oxygen species (ROS) generation in the brain, liver and ovary tissues increased with exposure duration at both reproductive phases while serum cortisol levels in ovulatory fish increased significantly compared to pre-ovulatory. Condition factor, gonadosomatic index and hepatosomatic index decreased in Zn-exposed fish. Brain GnRH and kisspeptin levels decreased significantly in the Zn-exposed group for both phases. GnIH was significantly higher in Zn-exposed fish. Serum FSH levels in pre-ovulatory and LH levels in ovulatory fish decreased gradually with an increase in the duration of exposure. Zn exposure reduced vitellogenin (Vtg) and estradiol (E2) in the liver and ovary with an increase in duration from both phases. Ovary maturation-inducing hormone (MIH) levels showed a decrease with exposure duration in ovulatory fish. Moreover, Zn-exposed ovulatory fish showed a degenerated oocyte nucleus due to the disintegration of the nuclear membrane. It might be inferred that Zn altered the HPGL regulatory system of M. vittatus reproduction at both the pre-ovulatory and ovulatory phases.

Melatonin as an Ameliorative Agent Against Cadmium- and Lead-Induced Toxicity in Fish: an Overview

Diverse anthropogenic activities and lack of knowledge on its consequences have promoted serious heavy metal contaminations in different aquatic systems throughout the globe. The non-biodegradable nature of most of these toxic heavy metals has increased the concern on their possible bioaccumulation in aquatic organisms as well as in other vertebrates. Among these aquatic species, fish are most sensitive to such contaminated water that not only decreases their chance of survivability in the nature but also increases the probability of biomagnifications of these heavy metals in higher order food chain. After entering the fish body, heavy metals induce detrimental changes in different vital organs by impairing multiple physiological and biochemical pathways that are essential for the species. Such alterations may include tissue damage, induction of oxidative stress, immune-suppression, endocrine disorders, uncontrolled cell proliferation, DNA damage, and even apoptosis. Although uncountable reports have explored the toxic effects of different heavy metals in diverse fish species, but surprisingly, only a few attempts have been made to ameliorate such toxic effects. Since, oxidative stress seems to be the underlying common factor in such heavy metal-induced toxicity, therefore, a potent and endogenous antioxidant with no side effect may be an appropriate therapeutic solution. Apart from summarizing the toxic effects of two important toxicants, i.e., cadmium and lead in fish, the novelty of the present treatise lies in its arguments in favor of using melatonin, an endogenous free radical scavenger and indirect antioxidant, in ameliorating the toxic effects of heavy metals in any fish species.

Comparative subchronic toxicity of copper and a tertiary copper mixture to early life stage rainbow trout (Oncorhynchus mykiss): impacts on growth, development, and histopathology

This research aimed to characterize and compare the subchronic impacts of Cu to a Cu, Cd, and Zn mixture in early life stages of rainbow trout (Oncorhynchus mykiss) by examining uptake, survival, growth, development, and histopathology parameters. To accomplish this, rainbow trout were exposed for 31 days from eyed embryos to the swim-up fry life stage to waterborne Cu (31, 47, 70, and 104 μg/L) individually or as mixture containing Cd (4.1, 6.2, 9.3, and 14 μg/L) and Zn (385, 578, 867, and 1300 μg/L). Exposures elicited pronounced effects on survival when Cu was administered as a mixture (LC25 = 32.9 μg/L Cu) versus individually (LC25 = 46.3 μg/L Cu). Mixtures of Cu, Cd, and Zn also elicited more pronounced sublethal toxicity relative to equivalent Cu treatments with respect to reduced yolk sac resorption and increased incidence and/or severity of gill, liver, and kidney lesions. Our findings of reduced body weight (EC10, Cu = 55.0 μg/L Cu; EC10, Cu+Cd+Zn = 58.9 μg/L Cu), yolk sac resorption (LOECCu = 70 μg/L Cu; LOECCu+Cd+Zn = 70 μg/L Cu), coelomic fat (LOECCu = 47 μg/L Cu; LOECCu+Cd+Zn = 70 μg/L Cu), and increased hepatocellular cytoplasmic vacuolation (LOECCu = 70 μg/L Cu; LOECCu+Cd+Zn = 47 μg/L Cu) collectively indicate a complicated metabolic interference by metals in exposed fish. These lethal and sublethal effects observed in the laboratory could translate to reduced survival and fitness of wild salmonid populations inhabiting waterbodies receiving wastewater or runoff containing multiple metals at elevated concentrations.

Challenges and Recommendations in Assessing Potential Endocrine-Disrupting Properties of Metals in Aquatic Organisms

New tools and refined frameworks for identifying and regulating endocrine-disrupting chemicals (EDCs) are being developed as our scientific understanding of how they work advances. Although focus has largely been on organic chemicals, the potential for metals to act as EDCs in aquatic systems is receiving increasing attention. Metal interactions with the endocrine system are complicated because some metals are essential to physiological systems, including the endocrine system, and nonessential metals can have similar physiochemical attributes that allow substitution into or interference with these systems. Consequently, elevated metal exposure could potentially cause endocrine disruption (ED) but can also cause indirect effects on the endocrine system via multiple pathways or elicit physiologically appropriate compensatory endocrine-mediated responses (endocrine modulation). These latter two effects can be confused with, but are clearly not, ED. In the present study, we provide several case studies that exemplify the challenges encountered in evaluating the endocrine-disrupting (ED) potential of metals, followed by recommendations on how to meet them. Given that metals have multiple modes of action (MOAs), we recommend that assessments use metal-specific adverse outcome pathway networks to ensure that accurate causal links are made between MOAs and effects on the endocrine system. We recommend more focus on establishing molecular initiating events for chronic metal toxicity because these are poorly understood and would reduce uncertainty regarding the potential for metals to be EDCs. Finally, more generalized MOAs such as oxidative stress could be involved in metal interactions with the endocrine system, and we suggest it may be experimentally efficient to evaluate these MOAs when ED is inferred. These experiments, however, must provide explicit linkage to the ED endpoints of interest. Environ Toxicol Chem 2023;42:2564-2579. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Exposure to acute waterborne cadmium caused severe damage on lipid metabolism of freshwater fish, revealed by nuclear lipid droplet deposition in hepatocytes of rare minnow

Cadmium (Cd) is a widely distributed aquatic toxic heavy metal with the potential to disrupt fish metabolism; however, more research is needed to clarify the underlying mechanisms. In the present study, rare minnows (Gobiocypris rarus) were used to detect the effects of cadmium on freshwater fish lipid metabolism and its underlying mechanism by histopathological observation, measurement of serum and liver biochemical indexes, and analysis of gene expression in terms of lipid oxidation, synthesis and transport. Here, severe damage, such as cytoplasmic lipid droplet (LD) accumulation, ectopic deposition of LDs, and the appearance of nuclear LDs (nLDs), was detected after exposure to 2.0 mg/L or higher concentrations (2.5 and 2.8 mg/L CdCl₂) for 96 h. Other damage included abnormal increases in rough endoplasmic reticulum (RER) lamellae in a fingerprint or concentric circle pattern and necrosis of hepatocytes, and which was observed in the livers of fish exposed to 2.0 mg/L CdCl_2.. Both hepatic and serum lipids, such as triglycerides and total cholesterol, were significantly increased after exposure to 2.0 mg/L CdCl₂, as was serum lipase (LPS). Hepatic lipase and lipoprotein lipase remained unchanged, in accordance with the unchanged hepatic mRNA transcripts of PPARɑ. Furthermore, the mRNA transcripts of both SCD and SQLE were significantly decreased. Moreover, hepatic and serum low-density and high-density lipoprotein cholesterol showed significant changes, which were accompanied by a significant increase and decrease in hepatic APOAI and APOB100 mRNA levels, respectively. All the results indicate the presence of severe damage to hepatic lipid metabolism and that disrupted lipid transport may play a key role in the accumulation of hepatic LDs. In addition, the hepatic nLDs of nonmammalian vertebrates and their location across the nuclear envelope are intriguing, suggesting that large-size nLDs are a common marker for severe liver damage.

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.

Parental cadmium exposure during the spawning period reduces cadmium sensitivity through the antioxidant system in rare minnow (Gobiocypris rarus) larvae

Cadmium (Cd) is a noxious heavy metal widely dispersed in aquatic systems. Parental Cd exposure of fish species at environmental concentrations has been shown to cause deformities and stunted growth in their offspring. However, the long-term effects and the mechanisms underlying parental Cd exposure in fish species on Cd sensitivity in their offspring remain unclear. To explore the impacts of parental Cd exposures on Cd sensitivity, rare minnow (Gobiocypris rarus) larvae whose parents were exposed to Cd at 0, 5 or 10 μg/L for 28 days were established. Results showed that parental Cd exposure in rare minnow increased the Cd content of its larvae. In terms of malformation rate, mortality rate and total length at 7 days of rare minnow larvae, parental Cd exposure at 5 or 10 μg/L reduced Cd sensitivity. Further mechanistic investigation demonstrated that parental Cd exposure significantly upregulated the expression of antioxidant gene regulated by nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-кB) in rare minnow larvae. In addition, parental Cd exposure significantly elevated the level of reactive oxygen species (ROS) and malondialdehyde (MDA), but markedly decreased catalase (CAT), superoxide dismutase (SOD) and oxidized glutathione (GST) activity. The impact of parental Cd exposure to metallothionein (MT) content and the expression of MT mRNA, a detoxifying metallothionein, showed that parental Cd exposure of rare minnow induced oxidative stress in the larvae. Meanwhile, these results indicated that parental Cd exposure in rare minnow reduced the Cd sensitivity of the larvae via activating the Nrf2-mediated antioxidant system. This project helps us to further understand the toxicological mechanism of Cd in fish species and properly assess its potential ecological risk.

Amelioration of Cd-induced bioaccumulation, hematological parameters, and heat shock protein-related genes by Vitamin C on common carp

The heavy metal cadmium (Cd) is a kind of non-essential toxic environmental pollutant with extremely long biological half-life, various toxic and sublethal effects on aquatic organisms, and many adverse effects on the organs of human and other mammals. Vitamin C is an essential micronutrient in aquatic feed, and an indispensable nutrient for maintaining physiological processes in different animals, including fish. The aim of this study was to evaluate the effects of administration of Vitamin C on bioaccumulation, hematological parameters and heat shock protein-related genes of common carp following Cd exposure. The fish were exposed to waterborne Cd at 0, 1 and 2 mg/L and administration Vitamin C at 150 and 300 mg/kg for 8 weeks. The results obtained indicate that Vitamin C can provide a significant protective effect on the toxicity of cadmium by inhibiting alterations in the levels of bioaccumulation, hematological parameters (including calcium, magnesium, glucose, alkaline phosphatase (ALP), glutamic-pyruvic transaminase (ALT), aspartate transaminase (AST), total protein, lactate dehydrogenase (LDH), cholesterol and lysozyme (LZM)) and heat shock protein-related genes (Hsp70, Hsp90, Hsp47 and Hsp60). Our study demonstrates that vitamin C has the potential to reduce heavy metal damage to common carp and improve immunity.

Taurine Alleviates Cadmium-Induced Toxicity via Genetically Specific Strategies in Two Strains of Gibel Carp (Carassius gibelio)

Our previous studies in gibel carp (Carassius gibelio) have shown that cadmium (Cd) exposure elicits deleterious effects depending on the genetic background, and thus we hypothesized that mitigation via nutritional intervention may vary between strains. Therefore, two gibel carp strains (the A and F strains) were fed diets supplemented with 0% or 1% taurine for 8 weeks prior to 96 h Cd exposure, and the responses of antioxidant pathways, endoplasmic reticulum (ER) stress, autophagy, and apoptosis were investigated. The results showed that taurine supplementation had no effect on the growth performance of gibel carp. After Cd exposure, histological damage to mitochondria and ER, induction of oxidative stress and antioxidant responses, occurrence of ER stress, and apoptotic signals were observed in the livers. Upon the diet effects, taurine supplementation alleviated the ER-stress-induced autophagy and apoptosis after Cd exposure and stimulated antioxidant pathways. Regarding the difference between strains, taurine played a protective role in alleviating Cd toxicity through the antioxidant response, ER stress, and autophagy in the F strain, whereas such effects were achieved by the attenuation of apoptosis in the A strain. Taken together, our results demonstrate the potential use of taurine in the mitigation of heavy metal toxicity in aquatic organisms.

Impacts of cadmium on male fertility: Lessons learnt so far

Cadmium (Cd) is one of the most dangerous heavy metals in the world. Globally, toxicities associated with cadmium and its attendant negative impact on humans and animals cannot be under-estimated. Cd is a heavy metal, and people are exposed to it through contaminated foods and smoking. Cd exerts its deleterious impacts on the testes (male reproductive system) by inducing oxidative stress, spermatogenic cells apoptosis, testicular inflammation, decreasing androgenic and sperm cell functions, disrupting ionic homeostasis, pathways and epigenetic gene regulation, damaging vascular endothelium and blood testes barrier. In association with other industrial by-products, Cd has been incriminated for the recent decline of male fertility rate seen in both man and animals. Understanding the processes involved in Cd-induced testicular toxicity is vital for the innovation of techniques that will help ameliorate infertility in males. In this review, we summed up recent studies on the processes of testicular toxicity and male infertility due to Cd exposure. Also, the usage of different compounds including phytochemicals, and plant extracts to manage Cd reprotoxicity will be reviewed.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Whole-cell biosensors for determination of bioavailable pollutants in soils and sediments: Theory and practice

The bioavailability of pollutants is a key factor affecting environmental risk. Whole-cell bioreporters are a demonstratedly effective tool for the investigation of pollutant bioavailability in water and soil/sediment. Unlike aqueous samples, transmittance of bioreporter optical signal is reduced in direct-contact assays with soil/sediment, which affects the accuracy of bioreporter-detected pollutant bioavailability. No studies have measured the magnitude and variability of soil/sediment effects on signal in direct-contact assays or how associated uncertainties influence results. In this study, we investigate the optical effects of soil/sediment particles in suspensions on bioreporter signal transmittance and quantify how variable these optical effects are from sample-to-sample. We find that neglecting bioreporter signal diminution by soil/sediment, as many studies do, can lead to order-of-magnitude errors in results, underestimating risk. Correction based on methods in ad hoc use (e.g. comparison to signal from non-inducible reporter or use of reference soil/sediment) are also problematic for some types of experiment, and could lead to errors in excess of 30%. Our findings have a sound basis in theory, and we provide recommendations concerning the most suitable type of approach to use for different experimental settings. Generally, if best accuracy is not needed to quantify bioavailability, for samples that have been ground, sieved, and are of reasonably uniform color, it may be possible to use a single or average correction factor, particularly for experiments performed at a single slurry concentration. For investigations studying bioavailability under varying solid-phase:water ratios (e.g., sorption/desorption), detailed compensation measurements are needed for independent variables, including each specific soil/sediment sample, slurry concentration, and in some cases bioreporter signal intensity. Our measurements and calculations indicate that best results are obtained when working in the region of ballistic photon transmittance. Findings herein will be useful in areas that require information on bioavailability, such as ecotoxicology and environmental risk assessment.

Zn-Enriched Bacillus cereus Alleviates Cd Toxicity in Mirror Carp (Cyprinus carpio): Intestinal Microbiota, Bioaccumulation, and Oxidative Stress

Cadmium (Cd) poisoning in humans and fish represents a significant global problem. Bacillus cereus (B. cereus) is a widely used probiotic in aquaculture. The objective of this study was to evaluate the potential of B. cereus in ameliorating Cd-induced toxicity in mirror carp. The biosorption rate of Zn for the B. cereus in 85.99% was significantly more than five strains. All fishes were exposed for 30 days to dietary ZnCl₂ (30mg/kg), waterborne Cd (1 mg/L), and/or dietary Zn-enriched B. cereus (Zn 30mg/kg and 10⁷cfu/g B. cereus). At 15 and 30 days, the fishes were sampled, and bioaccumulation, antioxidant activity, and intestinal microbiota were measured. Waterborne Cd exposure caused marked alterations in the composition of the microbiota. Dietary supplementation with Zn-enriched B. cereus can reduce the changes in the composition of intestinal microbiota in Cd exposure and decrease the pathogenic bacteria of Flavobacterium and Pseudomonas in Zn-enriched B. cereus groups. The results obtained indicate that Zn-enriched B. cereus can provide a significant protective effect on the toxicity of cadmium by inhibiting alterations in the levels of bioaccumulation and antioxidant enzyme including superoxide dismutase (SOD), catalase (CAT), total antioxidant (T-AOC), and malonaldehyde (MDA). Our results suggest that administration of Zn-enriched B. cereus has the potential to combat Cd toxicity in mirror carp.

Individual and joint effects of metal exposure on metabolic syndrome among Chinese adults

Growing evidence suggests that metal exposure contributes to metabolic syndrome (MetS), but little is known about the effects of combined exposure to metal mixtures. This cross-sectional study included 3748 adults who were recruited from the Medical Physical Examination Center of Tongji Hospital, Wuhan, China. The levels of 21 metal(loid)s in urine were measured by inductively coupled plasma mass spectrometry. MetS was diagnosed according to National Cholesterol Education Program's Adult Treatment Panel III recommendations. Multivariate logistic regression model was uesd to explore the effects of single-metal and multi-metal exposures. The elastic net (ENET) regularization with an environmental risk score (ERS) was performed to estimate the joint effects of exposure to metal mixtures. A total of 636 participants (17%) were diagnosed with MetS. In single metal models, MetS was positively associated with zinc (Zn) and negatively associated with nickel (Ni). In multiple metal models, the associations remained significant after adjusting for the other metals. In the joint association analysis, the ENET models selected Zn as the strongest predictor of MetS. Compared to the lowest quartile, the highest quartile of ERS was associated with an elevated risk of MetS (OR = 3.72; 95% CI: 2.77, 5.91; P-trend < 0.001). Overall, we identified that the combined effect of multiple metals was related to an increased MetS risk, with Zn being the major contributor. These findings need further validation in prospective studies.

Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries

Atresia of ovarian follicles, that is the degenerative process of germ cells and their associated somatic cells, is a complex process involving apoptosis, autophagy and heterophagy. Follicular atresia is a normal component of fish oogenesis and it is observed throughout the ovarian cycle, although it is more frequent in regressing ovaries during the postspawning period. An increased occurrence of follicular atresia above physiological rates reduces fish fecundity and even causes reproductive failure in both wild and captive-reared fish stocks, and hence, this phenomenon has a wide range of implications in applied sciences such as fisheries and aquaculture. The present article reviews the available literature on both basic and applied traits of oocyte loss by atresia, including its morpho-physiological aspects and factors that cause a supraphysiological increase of follicular atresia. Finally, the review presents the use of early follicular atresia identification in the selection process of induced spawning in aquaculture and the implications of follicular atresia in fisheries management.

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.

Toxic effects of cadmium and lead exposure on intestinal histology, oxidative stress response, and microbial community of Pacific white shrimp Litopenaeus vannamei

Cadmium (Cd) and lead (Pb) are two hazardous pollutants that threaten shrimp farming. The intestine is an important organ for digestion and immunity. We separately exposed Pacific white shrimp Litopenaeus vannamei to 500 μg/L Cd or 500 μg/L Pb seawater for 7 days, and 45 shrimp from each group were used to evaluate the changes of intestinal histopathological, oxidative stress, and microbiota composition. After Cd and Pb exposure, shrimp intestine appeared significant mucosal damage and oxidative stress, and the microbiota variation were induced. Specifically, the abundance of the phyla Bacteroidetes and Actinobacteria were induced, that of Proteobacteria and Firmicutes were deduced. The abundances of putative beneficial bacteria (Lactobacillus, Weissella, Demequina, Formosa and Ruegeria) and potentially pathogenic bacteria (Vibrio and Photobacterium) were fluctuated. Furthermore, the nutrient metabolic function of intestinal microbes was significantly altered. We concluded that Cd and Pb exposure had negative effects on the intestinal health of shrimp.

Cadmium-induced toxicity to amphibian tadpoles might be exacerbated by alkaline not acidic pH level

Heavy metal pollution in natural water bodies generally interacting with other environmental stressors produces toxic effects on aquatic organisms. However, toxicological studies exploring interactive effects of these stressors are still limited. Here, tadpoles of the Zhenhai brown frog (Rana zhenhaiensis) were exposed to a 3 × 3 factorial combination, with three cadmium (Cd) concentrations (0, 10 and 100 μg/L) and three pH levels (5.0, 7.23 and 9.0) throughout the developmental period to assess combined toxic effects of Cd × pH on tadpole growth, development and physiology. Nearly all measured traits [including survival, metamorphosis and abnormality rate, metamorphosis time, post-metamorphic size, hepatic metal content, locomotor performance, antioxidant enzyme activity, and erythrocytic nuclear abnormality (ENA) frequency] were affected by Cd exposure, indicating notable Cd-induced toxicity to R. zhenhaiensis tadpoles. The pH level and its interaction with Cd also had significant impacts on most measured traits, such as survival rate, metamorphosis time, froglet jumping distance, hepatic Cd content, ENA frequency. Acidic (or alkaline) environment itself was toxic to tadpoles. However, high pH (but not low pH) level appeared to exacerbate Cd-induced toxicity to tadpoles. Excess free hydrogen ions under acidic environments might inhibit Cd2+ ions binding to cell surface, which reduced Cd accumulation in tissues. Under alkaline environments, other forms of Cd complexes in the aqueous phase probably contributed to promoting Cd accumulation. Our results indicated that Cd exposure could interact with different pH levels, producing diverse combined toxicities to amphibian larvae.

Differential regulation of endoplasmic reticulum stress-induced autophagy and apoptosis in two strains of gibel carp (Carassius gibelio) exposed to acute waterborne cadmium

Previous studies illustrated that gibel carp F strain displays better lipid mobilization and antioxidant ability and compared to the A strain. We therefore hypothesized that the F strain would exhibit superior defense to cadmium exposure. Comparative studies were conducted between A and F strains using plasma stress biomarkers, histological observations, and analysis of hepatic molecular events to examine exposure to waterborne Cd (11.9 mg L^-1) for 48 h and 96 h. Waterborne Cd exposure stimulated stress response and hepatic metallothionein mRNA induction in both gibel carp strains confirming exposure. Antioxidant responses were stimulated to counteract Cd toxicity, suggested by the upregulation of mRNA levels of genes associated with nuclear factor erythroid 2-related factor 2 (nrf2) signaling. Cd exposure induced endoplasmic reticulum (ER) stress, meanwhile, branches of genes in unfolded protein response (UPR) were activated. Slight time-dependent effects were implied by greater ER stress, UPR, and apoptosis signals with the duration of Cd exposure. Genotype-specific effects were identified, revealing that the F strain showed greater stress at 96 h exposure and higher antioxidant response compared to the A strain, as indicated by the mRNA levels of genes in nrf2 signaling. ER stress and UPR were also stronger in the F strain after Cd exposure. In contrast, the A strain showed higher autophagy and apoptosis response compared to the F strain. Collectively, combined autophagy and apoptosis were triggered under ER stress, which might serve as defense strategies in both gibel carp strains. The F strain showed greater antioxidant detoxification response and UPR to mitigate Cd toxicity, whereas excessive ER stress contributed to higher autophagy and apoptosis in the A strain. The present study uncovered the differential regulation and defense strategies in fish strains exposed to metal exposure.

Individual and combined toxicogenetic effects of microplastics and heavy metals (Cd, Pb, and Zn) perturb gut microbiota homeostasis and gonadal development in marine medaka (Oryzias melastigma)

Currently, microplastics (MPs) attracted increased attention for their ubiquity and toxic properties. In this study, marine medaka was used to explore the individual and combined toxicity of heavy metals (HMs) and MPs on intestinal bacteria and gonadal development. After exposure to environmentally relevant concentrations of MPs and HMs, significant alterations of intestinal microbiota were found. The MPs treatment reduced the diversity and abundance of intestinal microbiota, while the HMs and MPs-HMs treatments increased them, which were confirmed by the abundance changes of Proteobacteria. According to the KEGG analysis, the metabolism and environmental information processing (EIP) pathways in the microbial community were significantly affected. This study showed that the MPs-HMs treatment caused a higher pollution load on the gut of the marine medaka, and triggered more significant changes of specific bacterial species and gut function in the males. However, during the gonadal development, HMs and MPs-HMs treatments resulted in empty follicles (EF) and follicular atresia (FA), and altered the gene expression levels related to hypothalamic-pituitary-gonadal (HPG) axis. In short, this study demonstrated that the reproductive disturbance was mainly due to HMs, but the combination of MPs and HMs did not strengthen the risk to the gonad development of the marine medaka.

Back to Nucleus: Combating with Cadmium Toxicity Using Nrf2 Signaling Pathway as a Promising Therapeutic Target

There are concerns about the spread of heavy metals in the environment, and human activities are one of the most important factors in their spread. These agents have the high half-life resulting in their persistence in the environment. So, prevention of their spread is the first step. However, heavy metals are an inevitable part of modern and industrial life and they are applied in different fields. Cadmium is one of the heavy metals which has high carcinogenesis ability. Industrial waste, vehicle emissions, paints, and fertilizers are ways of exposing human to cadmium. This potentially toxic agent harmfully affects the various organs and systems of body such as the liver, kidney, brain, and cardiovascular system. Oxidative stress is one of the most important pathways of cadmium toxicity. So, improving the antioxidant defense system can be considered as a potential target. On the other hand, the Nrf2 signaling pathway involves improving the antioxidant capacity by promoting the activity of antioxidant enzymes such as catalase and superoxide dismutase. At the present review, we demonstrate how Nrf2 signaling pathway can be modulated to diminish the cadmium toxicity.

Mitigative effects of zinc on cadmium-induced reproductive toxicity in the male freshwater crab Sinopotamon henanense

Cadmium (Cd) is a highly harmful environmental contaminant, which can cause reproductive toxicity. Zinc (Zn) is an essential trance element that may protect the organism from the harmful effects of Cd. However, the mechanism of Zn against Cd-induced reproductive toxicity remained to be elucidated. The aim of this study was to assess the effects of subchronic exposure to Cd on the relative testis weight (RTW), the histopathology, the activity of stress marker antioxidant enzymes, the level of lipid peroxidation of testis, as well as the mitigative effects of Zn on Cd-induced reproductive toxicity in male freshwater crab Sinopotamon henanense. For this purpose, male crabs were divided into 10 groups including a control group (without metals) and metal exposure groups with Cd alone in three concentrations and Cd combined with Zn in six concentrations for 14 days. The results showed that Cd evoked concentration-dependent reproductive toxicity of male Sinopotamon henanense as showed by decreased RTW, appearance of morphological lesions, increased SOD, CAT, GPx activity, and MDA levels. Nevertheless, Zn combined with Cd exposure significantly alleviated Cd-induced reproductive toxicity as proved by increased RTW, reappearance of normal histological morphology, increased SOD activity, recovered CAT and GPx activity, and decreased MDA levels in testis. Our study demonstrated that the application of Zn can mitigate Cd-induced reproductive toxicity by ameliorating the testicular oxidative stress and improving the antioxidant status.

Pre-hypoxia exposure inhibited copper toxicity by improving energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea

This study investigated the effects of moderate hypoxia pre-exposure on energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea exposed to Cu. Fish were pre-exposed to either normoxia or hypoxia (~3.0 mg L^-1, 42% O₂ saturation) for 48 h, and subsequently were subjected to either control (without Cu addition) or Cu (168 μg L^-1) under normoxic conditions for another 48 h. Copper exposure under normoxia induced Cu toxicity that increased mortality, the production of reactive oxygen species (ROS) and malondialdehyde, and aberrant hepatic mitochondrial ultrastructure. Interestingly, hypoxia pre-exposure improved energy metabolism, antioxidant ability and mitophagy response, and reduced the Cu content to inhibit Cu toxicity, reflecting the enhanced survival rate and reduced oxidative damage. In these processes, hypoxia-inducible factor-1α (HIF-1α), transcription factors NFE2-related nuclear factor 2 (Nrf2), and forkhead box O-3 (FoxO3) mRNA levels were correlated with expression of genes related to energy metabolism, antioxidant defence and mitophagy, respectively, indicating HIF-1α, Nrf2, and FoxO3 are required for the induction of their respective target genes. Overall, moderate hypoxia pre-exposure was able to generate adaptive responses to mitigate Cu-induced toxicological effects, underlining a central role of hormesis.

Neurobehavioural and biochemical responses associated with exposure to binary waterborne mixtures of zinc and nickel in rats

Environmental and occupational exposure to metal mixtures due to various geogenic and anthropogenic activities poses a health threat to exposed organisms. The outcome of systemic interactions of metals is a topical area of research because it may cause either synergistic or antagonistic effect. The present study investigated the impact of co-exposure to environmentally relevant concentrations of waterborne nickel (75 and 150 μg NiCl ₂ L^-1) and zinc (100 and 200 μg ZnCl₂ L^-1) mixtures on neurobehavioural performance of rats. Locomotor, motor and exploratory activities were evaluated using video-tracking software during trial in a novel arena and thereafter, biochemical and histological analyses were performed using the cerebrum, cerebellum and liver. Results indicated that zinc significantly (p < 0.05) abated the nickel-induced locomotor and motor deficits as well as improved the exploratory activity of exposed rats as verified by track plots and heat map analyses. Moreover, zinc mitigated nickel-mediated decrease in acetylcholinesterase activity, elevation in biomarkers of liver damage, levels of reactive oxygen and nitrogen species as well as lipid peroxidation in the exposed rats when compared with control. Additionally, nickel mediated decrease in antioxidant enzyme activities as well as the increase in tumour necrosis factor alpha, interleukin-1 beta and caspase-3 activity were markedly abrogated in the cerebrum, cerebellum and liver of rats co-exposed to nickel and zinc. Histological and histomorphometrical analyses evinced that zinc abated nickel-mediated neurohepatic degeneration as well as quantitative reduction in the widest diameter of the Purkinje cells and the densities of viable granule cell layer of dentate gyrus, pyramidal neurones of cornu ammonis 3 and cortical neurons in the exposed rats. Taken together, zinc abrogated nickel-induced neurohepatic damage via suppression of oxido-inflammatory stress and caspase-3 activation in rats.

Exposure to heavy metal-contaminated sediments disrupts gene expression, lipid profile, and life history traits in the midge Chironomus riparius

Despite the concern about anthropogenic heavy metal accumulation, there remain few multi-level ecotoxicological studies to evaluate their effects in fluvial ecosystems. The toxicity of field-collected sediments exhibiting a gradient of heavy metal contamination (Cd, Pb, and Zn) was assessed in Chironomus riparius. For this purpose, larvae were exposed throughout their entire life cycle to these sediments, and toxic effects were measured at different levels of biological organization, from the molecular (lipidomic analysis and transcriptional profile) to the whole organism response (respiration rate, shape markers, and emergence rate). Alterations in the activity of relevant genes, as well as an increase of storage lipids and decrease in membrane fluidity, were detected in larvae exposed to the most contaminated sediments. Moreover, reduced larval and adult mass, decrease of larval respiration rate, and delayed emergence were observed, along with increased mentum and mandible size in larvae and decreased wing loading in adults. This study points out the deleterious effects of heavy metal exposure at various levels of biological organization and provides some clues regarding the mode of toxic action. This integrative approach provides new insights into the multi-level effects on aquatic insects exposed to heavy metal mixtures in field sediments, providing useful tools for ecological risk assessment in freshwater ecosystems.

Identification and profiling of microRNAs responsive to cadmium toxicity in hepatopancreas of the freshwater crab Sinopotamon henanense

Background

Cadmium (Cd) is a ubiquitous environmental toxicant for aquatic animals. The freshwater crab, Sinopotamon henanense (S. henanense), is a useful model for monitoring Cd exposure since it is widely distributed in sediments whereby it tends to accumulate several toxicants, including Cd. In the recent years, the toxic effects of Cd in the hepatopancreas of S. henanense have been demonstrated by a series of biochemical analysis and ultrastructural observations as well as the deep sequencing approaches and gene expression profile analysis. However, the post-transcriptional regulatory network underlying Cd toxicity in S.henanense is still largely unknown.

Results

The miRNA transcriptional profile of the hepatopancreas of S. henanense was used to investigate the expression levels of miRNAs in response to Cd toxicity. In total, 464 known miRNAs and 191 novel miRNAs were identified. Among these 656 miRNAs, 126 known miRNAs could be matched with the miRNAs of Portunus trituberculatus, Eriocheir sinensis and Scylla paramamosain. Furthermore, a total of 24 conserved miRNAs were detected in these four crab species. Fifty-one differentially expressed miRNAs were identified in the Cd-exposed group, with 31 up-regulated and 20 down-regulated. Eight of the differentially expressed miRNAs were randomly selected and verified by the quantitative real-time PCR (qRT-PCR), and there was a general consistency (87.25%) between the qRT-PCR and miRNA transcriptome data. A total of 5258 target genes were screened by bioinformatics prediction. GO term analysis showed that, 17 GO terms were significantly enriched, which were mainly related to the regulation of oxidoreductase activity. KEGG pathway analysis showed that 18 pathways were significantly enriched, which were mainly associated with the biosynthesis, modification and degradation of proteins.

Conclusion

In response to Cd toxicity, in the hepatopancreas of S. henanense, the expressions of significant amount of miRNAs were altered, which may be an adaptation to resist the oxidative stress induced by Cd. These results provide a basis for further studies of miRNA-mediated functional adaptation of the animal to combat Cd toxicity.

Effects of cadmium exposure on sperm and larvae of the neotropical fish Prochilodus magdalenae

Cadmium (Cd) is a heavy metal with known deleterious effects on animal reproduction, decreasing the rate of fertilization of organisms such as fish. Prochilodus magdalenae is a very important fish species in Colombia, widely used by riparian communities from many rivers. Unfortunately, its population has been declining, whereas Cd seems to be more frequently detected in environmental matrices at Colombian ecosystems. The aim of this work was to determine the toxic effects of cadmium chloride on fertilization, sperm quality and mortality at 0, 1, 6 and 7 days post-hatching (dph) in this vulnerable species. The results indicated that Cd altered the fertilization and sperm quality by decreasing total motility and rapid and medium motilities of swimming spermatozoa. Results showed Cd produced 16.4 and 46.5% sperm motility inhibition, at 2.5 and 25 ppm, respectively. The heavy metal also impaired sperm curvilinear and straight-line velocities in a concentration-response dose. Cadmium-induced a dose-dependent effect on the mortality of the exposed larvae that depends on its development stage, with greater effects after 6 and 7 dph, observed at concentrations as low as 0.025 ppm. The results showed that the exposure to environmentally relevant Cd concentrations causes physiological changes in the initial stages of development of P. magdalenae, likely increasing the risk of reducing the fertility rate of this valuable fish species.

Magnitude of the mixture hormetic response of soil alkaline phosphatase can be predicted based on single conditions of Cd and Pb

In soil ecosystems, it is very challenging to predict mixture hormesis effects. In the present study, soil alkaline phosphatase (ALP) was selected to investigate and predict its potential hormetic responses under Cd and Pb stresses. Typical reverse U-shaped dose-response relationships between ALP activities and the single and combined Cd and Pb were observed, showing a hormetic response of soil itself. The maximum stimulatory magnitudes ranged in 8.0 - 8.6% under 0.004 - 0.2 mg/kg Cd and 80 - 400 mg/kg Pb, respectively. An enhanced stimulation of 15.7% occurred under the binary mixtures of 0.6 mg/kg Cd and 200 mg/kg Pb. In addition, a dosage-independent binary linear regression model was proposed based on an assumption of a linear relationship between the single and combined hormetic responses under Cd and Pb. Our model can well predict ALP's responses in the presence of the two metals' mixtures (p < 0.1). Our findings provided new understandings to hormesis in soil.

Effects of a chronic exposure to different water temperatures and/or to an environmental cadmium concentration on the reproduction of the threespine stickleback (Gasterosteus aculeatus)

Knowledge about combined effects of chemicals and temperature on reproductive capacity of fish are rare in literature, especially when it comes to the effects of chronic low-dose chemical exposure combined to the thermal stress. The aim of the study was to evaluate the single and combined effects of temperature (16, 18, 21 °C) and an environmentally relevant concentration of waterborne cadmium (1 µg L^-1, nominal concentration) on the reproductive outputs of threespine stickleback (Gasterosteus aculeatus), and their consequences on offspring survival parameters. The high temperature (21 °C) was the only factor that affected parental parameters (gonadosomatic index "GSI", and vitellogenin "VTG" particularly). On females, 21 °C had a stimulating effect on gonadal development evaluated by an early increase, followed by a sharp decrease of GSI, probably indicating gonadal atresia. Promoting effect of temperature was corroborated by an early production of VTG. In vitro fertilization assays showed interesting results, particularly cadmium effects. As it was supposed, high temperature had a negative impact on offspring parameters (significant decrease in survival and an increase of unhatched embryos). Parental exposure to the very low concentration of cadmium had also negative consequences on mortality rate (significant increase) and hatching rate (significant decrease). Our results indicate that in a global warming context, high temperature and its combination with contaminant may impact reproductive capacity of G. aculeatus, by decreasing parental investment (low eggs and/or sperm quality).

Sub-lethal effects of dimethoate alone and in combination with cadmium on biochemical parameters in freshwater snail, Galba truncatula

The objective of the present study was to evaluate the influence of the organophosphorus pesticide dimethoate and cadmium on biochemical parameters of a freshwater snail, Galba truncatula, in laboratory conditions. In 14 days, snails were exposed to 0, 100, 200, and 400 μg L^-1 of dimethoate and 0.0 and 1000 μg L^-1 of cadmium chloride. The results evidenced that dimethoate induces oxidative stress and alters biochemical parameters in freshwater snails. Cadmium also induced significant changes in biochemical parameters. The combination of the dimethoate and cadmium markedly increased the effects on G. truncatula. Dimethoate and cadmium mixture caused a decrease in Acetylcholinesterase (AChE), and Glucose-6-phosphate dehydrogenase (G6PDH) activities, glycogen, and total antioxidant capacity (TAN) levels, and increased aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), glutathione peroxidase (GPx), and catalase (CAT) activities, and malondialdehyde (MDA) level in exposed snails. The increased toxicity and bioaccumulation of cadmium after the exposure to the highest concentration of dimethoate indicates a synergistic effect leading to a reduced performance of the detoxification system in the snail. Dimethoate contributed to the bioconcentration of cadmium in snails and increased its toxic effects evidenced in biomarkers of oxidative stress and cell damage.

Negative effects of acute cadmium on stress defense, immunity, and metal homeostasis in liver of zebrafish: The protective role of environmental zinc dpre-exposure

In the study, zebrafish were exposed to 0 and 200 μg/L Zn for 8 weeks, and then both groups were transferred to water including 0, 100, and 200 μg/L Cd for 4 days, respectively. Acute Cd exposure caused negative effects on stress defense, immune, and metal transport systems by increasing lipid peroxidation, iNOS activity and mRNA levels of il-6 and inos, and decreasing Cu/Zn-SOD and HSP70 levels, and mRNA levels of sod1, cat, hsp70, p65, mtf-1, znt5, zip7, atp7a, and atp7b. Lipid peroxidation was significantly reduced by Zn pre-exposure under Cd exposure, which may be explained by the enhanced stress defense capacity and the weaken inflammatory response. Firstly, Zn pre-exposure increased MTs and HSP70 levels and CAT activity in Cd-free water, which may facilitate fish quick response to Cd. Secondly, Zn pre-exposure reduced Cd accumulation at 100 and 200 μg/L Cd, down-regulated il-6 and il-1β at 100 μg/L Cd and p65 at 200 μg/L Cd, and increased Cu/Zn-SOD and CAT activities at 200 μg/L Cd. Thirdly, Zn pre-exposure alone up-regulated transcription factors (hsf1, hsf2, and mtf-1, and nrf2) and their target genes (sod1, cat, hsp70, and mt2) under Cd exposure in a dose-dependent manner. It should be noted that Zn pre-exposure down-regulated several metal transport genes dramatically at 0 and 100 μg/L Cd, which may be an important mechanism for reducing Cd import into livers. Overall, long-term and environmental Zn pre-exposure mitigated Cd toxicity by the enhanced stress defense capacity and the down-regulated metal transport and inflammatory responses.

Responses of biomarkers in Atlantic salmon (Salmo salar) following exposure to environmentally relevant concentrations of complex metal mixture (Zn, Cu, Ni, Cr, Pb, Cd). Part II

The aim of this research was to assess interactions between metals at low exposure concentrations (Maximum-Permissible-Concentrations accepted for the inland waters in EU) and to assess possible influence of background exposure (10-times reduced concentration of a single metal) on toxicological significance of selected biomarkers in Salmo salar after treatment with metal mixture (Zn - 0.1, Cu - 0.01, Ni - 0.01, Cr - 0.01, Pb - 0.005 and Cd - 0.005 mg/L). The tissue-specific bioaccumulation, genotoxicity and cytotoxicity responses (erythrocytic nuclear abnormalities assay) in peripheral blood, kidneys, gills and liver erythrocytes of fish to metal mixtures were assessed after 14 days treatment. Treatment with primary mixture (MIX) or two variants of this mixture (Cr↓ (10 times reduced Cr⁶⁺ concentration) and Cu↓ (10 times reduced Cu²⁺ concentration)) induced the strongest responses in genotoxicity and cytotoxicity endpoints. Exposure to these mixtures highly affected Zn, Cu and Cd bioaccumulation in liver tissue. The highest amount of Ni accumulated was measured after Cd↓ treatment in all tissues. Treatments with reduced concentration of non-essential metal resulted in an increased accumulation of Pb, Ni, or Cd; treatments with reduced concentration of essential metal resulted in a reduced accumulation of certain metals (especially Cd and Pb) in tissues compared between treatments. Glucose content in blood and behavioural endpoints were evaluated after short-term exposure to metal mixtures (MIX, Cr↓, Cu↓). Significant increase in blood glucose concentration was measured after all treatments. These metal mixtures elicit significant behavioural alterations in fish. Consequently, this research revealed a significant influence of background exposure considering mixture toxicity.

The neurological toxicity of heavy metals: A fish perspective

The causes of neurodegenerative diseases are complex with likely contributions from genetic susceptibility and environmental exposures over an organism's lifetime. In this review, we examine the role that aquatic models, especially zebrafish, have played in the elucidation of mechanisms of heavy metal toxicity and nervous system function over the last decade. Focus is applied to cadmium, lead, and mercury as significant contributors to central nervous system morbidity, and the application of numerous transgenic zebrafish expressing fluorescent reporters in specific neuronal populations or brain regions enabling high-resolution neurodevelopmental and neurotoxicology research.

Effects of chronic exposure to waterborne copper and nickel in binary mixture on tissue-specific metal accumulation and reproduction in fathead minnow (Pimephales promelas)

The current study evaluated the interactive effects of chronic waterborne copper (Cu) and nickel (Ni) exposure on tissue-specific metal accumulation and reproductive performance in fathead minnow (Pimephales promelas). Fish trios (1 male: 2 female; n = 5-6) were exposed for 21 days to: (i) control (no added Cu or Ni), (ii) waterborne Cu (45 μg/L), (iii) waterborne Ni (270 μg/L), and (iv) binary mixture of waterborne Cu and Ni (45 and 270 μg/L, respectively). Fish fecundity (cumulative egg production) was found to be the most sensitive reproductive endpoint, and the interaction of Cu and Ni elicited an additive effect on egg production. Tissue-specific accumulation of both metals was not influenced by the interaction of Cu and Ni, except an increased Cu and Ni burden in the carcass and ovary, respectively, were recorded. The expressions of hepatic estrogen receptor genes (ER-α and ER-β) and the circulating estradiol level in females were also not affected by the metal-mixture treatment. However, co-exposure to waterborne Cu and Ni resulted in a significant downregulation of the hepatic vitellogenin gene in females, which was associated with the maximum upregulation of the hepatic metallothionein gene. In addition, a significant alteration of ovarian histopathology (decreased abundance of post-vitellogenic follicles, and increased follicular atresia) was also observed only in females exposed to Cu and Ni in mixture. Collectively, these observations suggest that chronic waterborne exposure to Cu and Ni in binary mixture may impair fish reproductive capacity by inducing histopathological damage in ovarian tissue, and disrupting of energy homeostasis in fish.