Developmental toxicity of copper in marine medaka (Oryzias melastigma) embryos and larvae

Investigation of copper-induced intestinal damage and proteome alterations in Takifugu rubripes: Potential health risks and environmental toxicology detection

Copper is one of the predominant water pollutants. Excessive exposure to copper can cause harm to animal health, affecting the central nervous system and causing blood abnormalities. Cuproptosis is a novel form of cell death that differs from previous programmed cell death methods. However, the impact of copper on the intestines remains unclear. Therefore, we investigated the effects of different concentrations of copper exposure on the intestinal proteome of Takifugu rubripes (T. rubripes). Relevant biomarkers were used to detect cuproptosis. We revealed the crosstalk relationship between cuproptosis and self-rescue at different concentrations, and discussed the feasibility of using potential cuproptosis indicators as anti-infection factors. We observed intestinal damage in the three copper exposure groups, especially in T. rubripes treated with 100 and 500 μg/L copper, with shedding and breakage of intestinal villus and fuzzy and loose structure of intestinal mucosa. The presence of copper stress not only causes cuproptosis but also oxidative damage caused by reactive oxygen species (ROS). The results of quantitative proteomics by TMT showed that compared to the 50 and 100 μg/L copper exposure groups, the expression of glutaminase, pyruvate kinase, and skin mucus lectin in the 500 μg/L group was significantly increased. The positive mediators COX5A and CTNNB1, as well as the negative mediators CD4 and FDXR, were found to be differentially expressed. Using the protein expression trends of cuproptosis indicator factors FDX1 and DLAT to indicate the concentration of copper ions in the environment. In addition, we found a new effect of promoting ferroptosis: providing additional copper ions can activate the phenomenon of ferroptosis. Our results expand our understanding of the potential health risks of copper in T. rubripes. At the same time, it is of great significance for the process of copper poisoning and the development of new environmental toxicology detection reagents.

Comparative effects of different metals on the Japanese medaka embryos and larvae

Rapid evaluation of the toxicity of metals using fish embryo acute toxicity is facilitative to ecological risk assessment of aquatic organisms. However, this approach has seldom been utilized for the comparative study on the effects of different metals to fish. In this study, acute and sub-chronic tests were used to compare the toxicity of Se(IV) and Cd in the embryos and larvae of Japanese medaka (Oryzias latipes). The embryos with different levels of dechorionation and/or pre-exposure were also exposed to Se(IV) and Cd at various concentrations. The results showed that the LC50-144 h of Cd was 1.3-5.2 folds higher than that of Se(IV) for the embryos. In contrast, LC50-96 h of Se(IV) were 200-400 folds higher than that of Cd for the larvae. Meanwhile, dechorionated embryos were more sensitive to both Se and Cd than the intact embryos. At elevated concentrations, both Se and Cd caused mortality and deformity in the embryos and larvae. In addition, pre-exposure to Cd at the embryonic stages enhanced the resistance to Cd in the larvae. However, pre-exposure to Se(IV) at the embryonic stages did not affect the toxicity of Se(IV) to the larvae. This study has distinguished the nuance differences in effects between Se(IV) and Cd after acute and sub-chronic exposures with/without chorion. The approach might have a potential in the comparative toxicology of metals (or other pollutants) and in the assessment of their risks to aquatic ecosystems.

Embryonic exposure to water accommodated fraction of crude oil inhibits reproductive capability in adult female marine medaka (Oryzias melastigma)

The water accommodated fraction (WAF) of spilled crude oil is a severe threat to the health of marine fish. This study was conducted to investigate the effects of short-term embryonic exposure to the WAF on the ovarian development and reproductive capability of F0 adult female marine medaka (Oryzias melastigma). Following embryonic exposure to the WAF with nominal total petroleum hydrocarbon concentrations of 0.5, 5, 50, and 500 μg/L for 7 days, the number of spawned eggs and gonadosomatic indices of F0 adult females were significantly reduced at 130 days postfertilization. In these F0 adult females, the proportion of mature oocytes was significantly lower, the level of 17β-estradiol was lower, and the level of testosterone was greater than those in control group. The mRNA levels of the follicle-stimulating hormone β subunit, luteinizing hormone β subunit, cytochrome P450 aromatase 19b, estrogen receptor α and β, and androgen receptor α and β genes were upregulated, while the mRNA level of the salmon-type gonadotropin-releasing hormone was downregulated in F0 adult females exposed to the WAF during the embryonic stage. Additionally, the methylation level of vitellogenin (vtg) in F0 adult females was significantly elevated, this might have, in turn, downregulated the mRNA level of vtg. The mortality rate of the unexposed F1 embryos was significantly increased and the hatching success was significantly reduced. These results collectively indicated the necessity of incorporating and evaluating the effects of short-term early-life exposure to crude oil in the assessment of risks to the reproductive health of marine fish.

Molecular variations to the proteome of zebrafish larvae induced by environmentally relevant copper concentrations

Contaminants are increasingly accumulating in aquatic environments and biota, with potential adverse effects on individual organisms, communities and ecosystems. However, studies that explore the molecular changes in fish caused by environmentally relevant concentrations of metals, such as copper (Cu), are limited. This study uses embryos of the model organism zebrafish (Danio rerio) to investigate effect of Cu on the proteome and amino acid (AA) composition of fish. Wild-type embryos at 24 h post-fertilisation were exposed to Cu (2 µg L-1 to 120 µg L-1) for 96 h and the number of healthy larvae were determined based on larvae that had hatched and did not display loss of equilibrium (LOE). The effect concentrations where Cu caused a 10 % (EC10) or 50 % (EC50) decrease in the number of healthy larvae were calculated as 3.7 µg L-1 and 10.9 µg L-1, respectively. Proteomics analysis of embryos exposed to the EC10 and EC50 concentrations of Cu revealed the proteome to differ more strongly after 48 h than 96 h, suggesting the acclimatisation of some larvae. Exposure to excess Cu caused differentially expressed proteins (DEPs) involved in oxidative stress, mitochondrial respiration, and neural transduction as well as the modulation of the AAs (Proline, Glycine and Alanine). This is the first study to suggest that LOE displayed by Cu-stressed fish may involve the disruption to GABAergic proteins and the calcium-dependent inhibitory neurotransmitter GABA. Moreover, this study highlights that proteomics and AA analysis can be used to identify potential biomarkers for environmental monitoring.

Effect of Pb, Cu and Zn on development and Wnt/β-catenin signaling pathway genes expression of Ctenopharyngodon idella

Pollution of the aquatic environment with heavy metals is a serious environmental problem, since they accumulate in aquatic organisms and can affect their development and worsen their condition. According to the scheme of Fig. 1 zinc (Zn), copper (Cu) or lead (Pb) were studied when exposed to concentrations of: Zn (0.01; 0.1; 1 mg/L), Cu (0.001; 0.01; 0.1 mg/L), Pb (0.006; 0.06; 0.6 mg/L) for 144 h after fertilization (hpf) on the grass carp (Ctenopharyngodon idella), one of the important commercial fish species of Kazakhstan, the activity of superoxide dismutase (SOD) and the expression of genes of the Wnt/β-catenin signaling pathway involved in development. All metals significantly reduced survival, hatching rate, and changed biometric parameters and heart rate of cupid larvae. In addition, these metals (mainly Pb and Cu) inhibited superoxide dismutase (SOD) activity and mRNA transcription of genes encoding genes of the Wnt/β-catenin signaling pathway. These results showed that Pb, Cu and Zn not only affect the survival and development of fish at an early stage of life, but also cause oxidative stress and prevent fish detoxification.

Comprehensive effects of salinity, dissolved organic carbon and copper on mortality, osmotic regulation and bioaccumulation of copper in Oryzias melastigma

Cu, as an essential and toxic element, has gained widespread attention. Both salinity and dissolved organic carbon (DOC) are known to influence Cu toxicity in marine organisms. However, the intricate interplay between these factors and their specific influence on Cu toxicity remains ambiguous. So, this study conducted toxicity tests of Cu on Oryzias melastigma. The experiments involved three salinity levels (10, 20, and 30 ppt) and three DOC levels (0, 1, and 5 mg/L) to comprehensively investigate the underlying mechanisms of toxicity. The complex toxic effects were analyzed by mortality, NKA activity, net Na+ flux and Cu bioaccumulation in O. melastigma. The results indicate that Cu toxicity is notably influenced by both DOC and salinity. Interestingly, the discernible variation in Cu toxicity across different DOC levels diminishes as salinity levels increase. The presence of DOC enhances the impact of salinity on Cu toxicity, especially at higher Cu concentrations. Additionally, Visual MINTEQ was utilized to elucidate the chemical composition of Cu, revealing that DOC had a significant impact on Cu forms. Furthermore, we observed that fluctuations in salinity lead to the inhibition of Na+/K+-ATPase (NKA) activity, subsequently hindering the inflow of Na+. The effects of salinity and DOC on the bioaccumulation of copper were not significant. The influence of salinity on Cu toxicity is mainly through its effect on the osmotic regulation and biophysiology of O. melastigma. Additionally, DOC plays a crucial role in the different forms of Cu. Moreover, DOC-Cu complexes can be utilized by organisms. This study contributes to understanding the mechanism of copper's biological toxicity in intricate marine environments and serves as a valuable reference for developing marine water quality criteria for Cu.

A study on the subchronic toxicity of triclocarban to the early-life development of oryzias melastigma and focused on the analysis of osmoregulatory regulation mechanisms

Triclocarban (TCC), a novel antimicrobial agent found in personal care products, has been extensively detected in marine environments. However, research on the toxic effects of TCC on marine organisms remains inadequate. This study delved into the subchronic toxic effects of TCC on the early life stages of marine medaka (Oryzias melastigma, O. melastigma), revealing that TCC could reduce embryo heart rate and hatching rate while diminishing the survival rate of larvae. Biomarker assays indicated that TCC could inflict damage on the embryos' antioxidant and nervous systems. Transcriptomic analysis suggested that TCC could impact cell growth, reproduction, and various life processes, activating cancer signaling pathways, increasing the likelihood of cancer, and exerting toxic effects on the immune and osmoregulatory systems. To validate and enhance our understanding of TCC's unique toxic impact on the osmoregulatory system of O. melastigma, we conducted homology modeling and molecular docking analyses on the protein involved in osmoregulation. The study intuitively revealed the potential binding affinity of TCC to sodium/potassium-transporting ATPase subunit alph (ATP1A1), indicating its ability to disrupt osmotic balance in marine fish by affecting this target protein. In summary, the results of this study will further enhance our comprehension of the potential toxic effects and mechanisms of TCC on the early stages of marine fish, with a specific focus on its unique toxic effects in osmoregulation.

Receptor model-based sources and risk assessment of metals in sediment of the coastal construction-oriented aquatic system in Bangladesh

Metal pollution in sediment from construction areas raises ecological and health concerns, yet source-based sediment pollution in Bangladesh remains understudied. Our investigation focused on fifteen locations in the Kohelia River and the coastal regions near the Matarbari projects (Matarbari Power Plant, Matarbari Deep Seaport), assessing metal concentrations' sources and impacts on ecology and human well-being. Sediment quality indices indicated high Cd and Cr contamination, with sites near Matarbari projects being the most polluted. The positive matrix factorization model identified three anthropogenic sources and mixed sources. Matarbari projects contributed significantly to As (67.9 %), Mn (50.25 %), Cd (48.35 %), and Cr (41.0 %), while ship-breaking yards contributed Fe (58.0 %), Zn (55.5 %), Pb (53.8 %), and Cu (36.1 %). Ecological indices showed different impacts on aquatic life from metal pollution, but cancer risk levels stayed below the threshold set by the US Environmental Protection Agency. These findings underscore the need for targeted measures to address metal pollution.

Combined toxicity of microplastics and copper on Goniopora columns

As microplastics (MP) become ubiquitous, their interactions with heavy metals threatens the coral ecosystem. This study aimed to assess the combined toxicity of MP and copper (Cu) in the environment of coral. Goniopora columna was exposed to polyethylene microplastics (PE-MP) combined with Cu2+ at 10, 20, 50, 100, and 300 μg/L for 7 days. Polyp length and adaptability were recorded daily, and coral samples were collected at 1, 3, 5, and 7 days to analyse zooxanthellae density and antioxidant activity. Tissue observations and the analysis of MP and Cu2+ accumulation were conducted on the 7th day. After 1 day of exposure, PE-MP combined with different concentrations of Cu2+ significantly decreased polyp length and adaptability compared with PE-MP alone. Simultaneously, a significant increase in malondialdehyde (MDA) content, lead to coral oxidative stress, which was a combined effect with PE-MP. After 3 days of exposure, PE-MP combined with Cu2+ at >50 μg/L significantly reduced zooxanthellae density, damaging the coral's symbiotic relationship. In antioxidant enzyme activity, superoxide dismutase (SOD) activity decreased significantly after 1 day of exposure. After 3 days of exposure, glutathione peroxidase (GPx) activity significantly increased with Cu2+ at >20 μg/L. After 5 days of exposure, PE-MP combined with different concentrations of Cu2+ significantly reduced catalase (CAT), glutathione (GSH), and glutathione transferase (GST) activity, disrupting the antioxidant enzyme system, and acting antagonistically to PE-MP alone. Tissue observations revealed that the PE-MP combined with Cu2+ at >50 μg/L caused severe mesenteric atrophy, vacuolar, and Cu2+ accumulation in the coral mesenteric compared with PE-MP alone. The results suggest that combined exposure of PE-MP and copper leads to more severe oxidative stress, disruption antioxidant enzyme system, tissue damage, and Cu2+ accumulation, resulting in a significant maladaptation of corals to the environment.

Unveiling the silent threat: Heavy metal toxicity devastating impact on aquatic organisms and DNA damage

Heavy metal pollution has significant impacts on aquatic fauna and flora. It accumulates in marine organisms, both plants and animals, which are then consumed by humans. This can lead to various health problems, such as organ damage and the development of cancer. Additionally, this pollution causes biological magnification, where the toxicity concentration gradually increases as aquatic organisms continuously accumulate metals. This process results in apoptotic mechanisms, antioxidant defence, and inflammation, which are reflected at the gene expression level. However, there is limited research on specific heavy metals and their effects on fish organs. The concentration of metal contamination and accumulation in different tropical environments is a concern due to their toxicity to living organisms. Therefore, this review focuses on determining the influences of metals on fish and their effects on specific organs, including DNA alterations.

Assessing the disparity: comparative toxicity of Copper in zebrafish larvae exposes alarming consequences of permissible concentrations in Brazil

Copper (Cu) is a naturally occurring metal with essential micronutrient properties. However, this metal might also pose increased adverse environmental and health risks due to industrial and agricultural activities. In Brazil, the maximum allowable concentration of Cu in drinking water is 2 mg/L. Despite this standard, the impact of such concentrations on aquatic organisms remains unexplored. This study aimed to evaluate the toxicity of CuSO4 using larval zebrafish at environmentally relevant concentrations. Zebrafish (Danio rerio) larvae at 72 hr post-fertilization (hpf) were exposed to nominal CuSO4 concentrations ranging from 0.16 to 48 mg/L to determine the median lethal concentration (LC50), established at 8.4 mg/L. Subsequently, non-lethal concentrations of 0.16, 0.32, or 1.6 mg/L were selected for assessing CuSO4 -induced toxicity. Morphological parameters, including body length, yolk sac area, and swim bladder area, were adversely affected by CuSO4 exposure, particularly at 1.6 mg/L (3.31 mm ±0.1, 0.192 mm2 ±0.01, and 0.01 mm2 ±0.05, respectively). In contrast, the control group exhibited values of 3.62 mm ±0.09, 0.136 mm2 ±0.013, and 0.3 mm2 ±0.06, respectively. Behavioral assays demonstrated impairments in escape response and swimming capacity, accompanied by increased levels of reactive oxygen species (ROS) and lipid peroxidation. In addition, decreased levels of non-protein thiols and reduced cellular viability were noted. Data demonstrated that exposure to CuSO4 at similar concentrations as those permitted in Brazil for Cu adversely altered morphological, biochemical, and behavioral endpoints in zebrafish larvae. This study suggests that the permissible Cu concentrations in Brazil need to be reevaluated, given the potential enhanced adverse health risks of exposure to environmental metal contamination.

Single and mixture toxicity of cadmium and copper to swim bladder in early life stages of Japanese medaka (Oryzias latipes)

Toxicity observed in aquatic ecosystems often cannot be explained by the action of a single pollutant. Likewise, evaluation standards formulated by a single effect cannot truly reflect the environmental quality requirements. The study of mixtures is needed to provide environmental relevance and knowledge of combined toxicity. In this study, the embryos of Japanese medaka (Oryzias latipes) were treated with individual and binary mixture of copper (Cu) and cadmium (Cd) until 12 days post-fertilization (dpf). Hatching, mortality, development, histology and gene expression were assessed. Our results showed that the highest concentration mixture of Cd (10 mg/L) and Cu (1 mg/L) affected survival, hatching time and hatching success. Occurrence of uninflated swim bladder was the highest (value) with exposure to 10 mg/L Cd. Swim bladder was commonly over-inflated in a mixture (0.1 mg/L Cd + 1.0 mg/L Cu) exposure. Individuals exposed to the mixture (0.1 Cd + 1.0 Cu mg/L) showed up to a 7.69% increase in swim bladder area compared to the control group. The mixtures containing 0.1 or 10 mg/L Cd, each with 1.0 mg/L Cu resulted in significantly increased of Pbx1b expression, higher than any Cd or Cu alone (p < 0.01). In the co-exposure group (0.1/10 Cd + 1.0 Cu mg/L), Pbx1b expression was found at 12 dpf but not 7 dpf in controls. Higher concentrations of Cd may progressively reduce Pbx1b expression, potentially explaining why 75% of individuals in the 10 mg/L Cd group failed to inflate their swim bladders. Additionally, the swim bladder proved to be a valuable bio-indicator for biological evaluation.

Abnormality of mussel in the early developmental stages induced by graphene and triphenyl phosphate: In silico toxicogenomic data-mining, in vivo, and toxicity pathway-oriented approach

Increasing number of complex mixtures of organic pollutants in coastal area (especially for nanomaterials and micro/nanoplastics associated chemicals) threaten aquatic ecosystems and their joint hazards are complex and demanding tasks. Mussels are the most sensitive marine faunal groups in the world, and their early developmental stages (embryo and larvae) are particularly susceptible to environmental contaminants, which can distinguish the probable mechanisms of mixture-induced growth toxicity. In this study, the potential critical target and biological processes affected by graphene and triphenyl phosphate (TPP) were developed by mining public toxicogenomic data. And their combined toxic effects were verified by toxicological assay at early developmental stages in filter-feeding mussels (embryo and larvae). It showed that interactions among graphene/TPP with 111 genes (ABCB1, TP53, SOD, CAT, HSP, etc.) affected phenotypes along conceptual framework linking these chemicals to developmental abnormality endpoints. The PPAR signaling pathway, monocarboxylic acid metabolic process, regulation of lipid metabolic process, response to oxidative stress, and gonad development were noted as the key molecular pathways that contributed to the developmental abnormality. Enriched phenotype analysis revealed biological processes (cell proliferation, cell apoptosis, inflammatory response, response to oxidative stress, and lipid metabolism) affected by the investigated mixture. Combined, our results supported that adverse effects induced by contaminants/ mixture could not only be mediated by single receptor signaling or be predicted by the simple additive effect of contaminants. The results offer a framework for better comprehending the developmental toxicity of environmental contaminants in mussels and other invertebrate species, which have considerable potential for hazard assessment of coastal mixture.

Hexavalent Chromium Inhibited Zebrafish Embryo Development by Altering Apoptosis- and Antioxidant-Related Genes

This study aimed to assess the effects of hexavalent chromium on zebrafish (Danio rerio) embryo development. The zebrafish embryos were treated with solutions containing chromium at different concentrations (0.1, 1, 3.125, 6.25, 12.5, 50, and 100 µg/mL). The development of zebrafish embryos was estimated by the determination of survival rate, heart rate, and the measurement of larvae body length. Real time RT-PCR and Western blot were performed to assess the expression of apoptosis- and antioxidant-related genes. The results showed that the reduced survival rate of zebrafish embryos and larvae was associated with an increase in chromium concentration. The exposure of higher concentrations resulted in a decrease in body length of zebrafish larvae. In addition, a marked increase in heart rate was observed in the zebrafish larvae under chromium treatment, especially at high concentrations. The real-time RT-PCR analysis showed that the transcript expressions for cell-cycle-related genes (cdk4 and cdk6) and antioxidant-related genes (sod1 and sod2) were downregulated in the zebrafish embryos treated with chromium. Western blot analysis revealed the upregulation of Caspase 3 and Bax, while a downregulation was observed in Bcl2. These results indicated that hexavalent chromium induced changes in zebrafish embryo development by altering apoptosis- and antioxidant-related genes.

Exposure to manganese (II) chloride induces developmental toxicity, oxidative stress and inflammatory response in Marine medaka (Oryzias melastigma) embryos

Manganese (Mn) is an essential metal for organisms, but high levels can induce serious toxicity. To date, the toxic mechanism of Mn to marine fish is still poorly understood. In the present study, Oryzias melastigma embryos were exposed to different concentrations of MnCl₂ (0-152.00 mg/L) to investigate its effect on early development. The results showed that exposure to MnCl₂ caused developmental toxicity to embryos, including increased heart rate, delayed hatching time, decreased hatching rate and increased malformation rate. MnCl₂ exposure could induce oxidative stress in O. melastigma embryos, as indicated by increased the contents of malondialdehyde (MDA) and the activities of the antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT)). The heart might be an important target organ for MnCl₂ because of cardiac malformations and disruption in the expression of cardiac development-related genes (ATPase, epo, fg8g, cox1, cox2, bmp4 and gata4). In addition, the expression levels of stress- (omTERT and p53) and inflammation-related genes (TNFα and il1β) were significantly up-regulated, suggesting that MnCl₂ can trigger stress and inflammatory response in O. melastigma embryos. In conclusion, this study demonstrated that MnCl₂ exposure can induce developmental toxicity, oxidative stress and inflammatory response in O. melastigma embryos, providing insights into the toxic mechanism of Mn to the early development of marine fish.

Bioaccumulation and Bioremediation of Heavy Metals in Fishes-A Review

Heavy metals, the most potent contaminants of the environment, are discharged into the aquatic ecosystems through the effluents of several industries, resulting in serious aquatic pollution. This type of severe heavy metal contamination in aquaculture systems has attracted great attention throughout the world. These toxic heavy metals are transmitted into the food chain through their bioaccumulation in different tissues of aquatic species and have aroused serious public health concerns. Heavy metal toxicity negatively affects the growth, reproduction, and physiology of fish, which is threatening the sustainable development of the aquaculture sector. Recently, several techniques, such as adsorption, physio-biochemical, molecular, and phytoremediation mechanisms have been successfully applied to reduce the toxicants in the environment. Microorganisms, especially several bacterial species, play a key role in this bioremediation process. In this context, the present review summarizes the bioaccumulation of different heavy metals into fishes, their toxic effects, and possible bioremediation techniques to protect the fishes from heavy metal contamination. Additionally, this paper discusses existing strategies to bioremediate heavy metals from aquatic ecosystems and the scope of genetic and molecular approaches for the effective bioremediation of heavy metals.

Effects of lipophilic phycotoxin okadaic acid on the early development and transcriptional expression of marine medaka Oryzias melastigma

The lipophilic okadaic acid (OA)-group toxins produced by some species of Dinophysis spp. and Prorocentrum spp. marine dinoflagellates have been frequently and widely detected in natural seawater environments, e.g. 2.1∼1780 ng/L in Spanish sea and 5.63∼27.29 ng/L in the Yellow Sea of China. The toxicological effects of these toxins dissolved in seawater on marine fish is still unclear. Effects of OA on the embryonic development and 1-month old larvae of marine medaka (Oryzias melastigma) were explored and discussed in this study. Significantly increased mortality and decreased hatching rates occurred for the medaka embryos exposed to OA at 1.0 μg/mL. Diverse malformations including spinal curvature, dysplasia and tail curvature were also observed in the embryos exposed to OA and the heart rates significantly increased at 11 d post fertilization. The 96 h LC₅₀ of OA for 1-month old larvae was calculated at 3.80 μg/mL. The reactive oxygen species (ROS) was significantly accumulated in medaka larvae. Catalase (CAT) enzyme activity was significantly increased in 1-month old larvae. Acetylcholinesterase (AChE) activity significantly increased with a dose-dependent pattern in 1-month old larvae. Differentially expressed genes (DEGs) were enriched in 11 KEGG pathways with Q value < 0.05 in 1-month old medaka larvae exposed to OA at 0.38 μg/mL for 96 h, which were mainly related to cell division and proliferation, and nervous system. Most of DEGs involved in DNA replication, cell cycle, nucleotide excision repair, oocyte meiosis, and mismatch repair pathways were significantly up-regulated, while most of DEGs involved in synaptic vesicle cycle, glutamatergic synapse, and long-term potentiation pathways were markedly down-regulated. This transcriptome analysis demonstrated that a risk of cancer developing was possibly caused by OA due to DNA damage in marine medaka larvae. In addition, the neurotoxicity of OA was also testified for marine fish, which potentially cause major depressive disorder (MDD) via the up-regulated expression of NOS1 gene. The genotoxicity and neurotoxicity of OA to marine fish should be paid attention to and explored further in the future.

Acute and Chronic Effects of Crude Oil Water-Accommodated Fractions on the Early Life Stages of Marine Medaka (Oryzias melastigma, McClelland, 1839)

Oil spill is a major marine environmental pollution issue. Research regarding the long-term effects of oil spills on the early life stage of marine fish is still limited. In this study, the potential adverse impact of crude oil from one oil spill accident which occurred in the Bohai Sea on the early life stages of marine medaka (Oryzias melastigma, McClelland, 1839) was evaluated. A 96-h acute test (larvae) and a 21-d chronic test (embryo-larvae) of water-accommodated fractions (WAFs) from crude oil were conducted, respectively. The results of the acute test showed that only the highest concentration of WAFs (100.00%) significantly affected the mortality of larvae (p < 0.01) and that the 96 h-LC₅₀ was 68.92% (4.11 mg·L^-1 expressed as total petroleum hydrocarbons (TPHs)). Larval heart demonstrated histopathological alterations in all WAF-exposed groups. The chronic test results showed that, except for larval mortality, the total hatching success (%)/hatching time of embryos in WAF treatments was not significantly different from those of the control group (p > 0.05), and no malformation was found in surviving larvae after 21 d of exposure. Nevertheless, the exposed embryos and larvae in the highest concentration of WAFs (60.00%) demonstrated significantly reduced heart rate (p < 0.05) and increased mortality (p < 0.01), respectively. Overall, our results indicated that both acute and chronic WAF exposures had adverse impacts on the survival of marine medaka. In the early life stages, the heart of the marine medaka was the most sensitive organ which showed both structural alteration and cardiac dysfunction.

Bisphenol A alters sexual dimorphism and gene expression in marine medaka Oryzias melastigma

Bisphenol A (BPA) is an endocrine disruptor that is present in freshwater and marine environments. However, conclusive evidence for the toxicity of chronic BPA exposure to marine fishes remains lacking. Therefore, we investigated the influence of BPA on male marine medaka (Oryzias melastigma). BPA exposure induced formation of testis-ova at 2610 µg/L, and male-type anal fins became more female type in a concentration-dependent manner. Some males with female-type anal fins had normal testes, indicating that anal fin shape is more sensitive to BPA. Gonadal soma-derived factor (gsdf) expression decreased after BPA exposure in the 746 and 2610 µg/L exposure groups, although the changes were not statistically significant. Additionally, liver vitellogenin (vtg) expression increased in a dose-dependent manner and was significantly higher in all exposure groups. vtg and gsdf are likely to be useful biomarkers for the impact of estrogenic endocrine disrupters in O. melastigma.

Acute Copper Toxicity Displays a Nonmonotonic Relationship with Age Across the Medaka (Oryzias latipes) Life Span

The ability of an organism to cope with environmental stressors varies across the life span because of developmental stage-specific responses and age-related functional declines. In the present study, we examined the effect of age on acute copper toxicity in Japanese medaka (Oryzias latipes). We first determined the median lethal concentration (LC50) at 96 h for embryos, 7-day-old fry, and 6-month-old medaka. Embryos were exposed to 0, 15, 30, 60, 125, 250, and 500 ppb CuSO₄ through hatching. Fry were exposed to 0, 20, 50, 75, 100, 150, 250, and 500 ppb CuSO₄ for 96 h. Adult fish were exposed to 0, 100, 150, 200, 250, and 300 ppb CuSO₄ for 96 h. The 96-h LC50 was 804 ppb for embryos, 262 ppb for embryonically exposed larvae, 60.3 ppb for 7-day-old fry, and 226 ppb for adults. We then challenged cohorts of fish aged 2, 3, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, and 16 months with a 225-ppb CuSO₄ exposure to determine the acute toxicity across the life span. The fish exhibited a bimodal tolerance to copper, with tolerance peaking in 2- and 3-month-old fish and again at 10 and 11 months of age. Our data demonstrate that copper sensitivity is dynamic throughout the medaka life span and may be influenced by trade-offs with reproduction. Environ Toxicol Chem 2022;41:2999-3006. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Same sensitivity with shorter exposure: behavior as an appropriate parameter to assess metal toxicity

The exposure of animals to toxicants may cause a depletion in the energy uptake, which compromises reproduction and growth. Although both parameters are ecologically relevant, they usually need long-term bioassays. This is a handicap for the availability of toxicological data for environmental risk assessment. Short-term bioassays conducted with environmental concentrations, and using relevant ecological parameters sensitive to short-term exposures, such as behavior, could be a good alternative. Therefore, to include this parameter in the risk assessment procedures, it is relevant the comparison of its sensitivity with that of growth and reproduction bioassays. The study aim was the assessment of differences between endpoints based on mortality, behaviour, reproduction, and growth for the toxicity of metals on aquatic animals. We used the ECOTOX database to gather data to construct chemical toxicity distribution (CTD) curves. The mean concentrations, the mean exposure time, and the ratio between the mean concentration and the exposure time were compared among endpoints. Our results showed that behavioral, growth, and reproduction bioassays presented similar sensitivity. The shortest exposure was found in behavioral and reproduction bioassays. In general, the amount of toxicant used per time was lower in growth and reproduction bioassays than in behavioral and mortality bioassays. We can conclude that, for metal toxicity, behavioral bioassays are less time-consuming than growth bioassays. As the sensitivity of behavior was similar to that of growth and reproduction, this endpoint could be a better alternative to longer bioassays.

Melatonin protects porcine oocyte from copper exposure potentially by reducing oxidative stress potentially through the Nrf2 pathway

Copper is widely used as a feeding additive to promote livestock growth. However, excessive copper can be excreted with feces, causing heavy metal pollution and aggravating environmental problems. At the same time, studies have found that excess copper can cause damage to reproductive function and reduce gamete quality. Here, we explored the effects of adding different concentrations of copper to the culture medium on porcine oocytes. First polar body extrusion rate, embryo development, and intracellular levels of reactive oxygen species (ROS), mitochondrial membrane potential (MMP) ΔΨm, adenosine triphosphate(ATP) content, and acetylation of lysine 9 on histone H3 protein subunit (H3K9ac) were assessed. Results demonstrated that Cu exposure causes abnormalities in mitochondrial function and epigenetic modification, resulting in increased oxidative stress and levels of ROS, ultimately leading to a decreased porcine oocyte quality. In addition, we found melatonin can protect porcine oocytes from those damages. Notably, Nrf2 protein expression was significantly increased by copper exposure, meanwhile, Nrf2 signaling pathway inhibitor ML385 significantly attenuated the protective role of melatonin on oxidative stress induced by copper exposure. In summary, our study demonstrates that copper activates the Nrf2 pathway and impairs oocyte maturation by inducing oxidative stress, leading to poor quality of porcine oocytes, and the changes can be reversed by melatonin.

Impacts of heavy metals on early development, growth and reproduction of fish - A review

Heavy metals pollution causes a threat to the aquatic environment and to its inhabitants when their concentrations exceed safe limits. Heavy metals cause toxicity in fish due to their non-biodegradable properties and their long persistence in the environment. This review investigated the effects of heavy metals on early development, growth and reproduction of fish. Fish embryos/larvae and each developmental stage of embryo respond differently to the intoxication and vary from species to species, types of metals and their mode of actions, concentration of heavy metals and their exposure time. Many of the heavy metals are considered as essential nutrient elements that positively improve the growth and feed utilization of fishes but upon crossing the maximum tolerable limit these metals cause not only a hazard to fish health but also to human consumers and the disruption of ecological systems. Reduced gonadosomatic index (GSI), fecundity, hatching rate, fertilization success, abnormal shape of reproductive organs, and finally failure of reproduction in fish have been attributed to heavy metal toxicity. In summary, this review sheds light on the manipulation of fish physiology by heavy metals and seeks to raise sensitivity to the prevention and control of aquatic environmental contamination, particularly from heavy metals.

Exposure to trace levels of metals and fluoroquinolones increases inflammation and tumorigenesis risk of zebrafish embryos

Exposure to trace-level heavy metals and antibiotics may elicit metabolic disorder, alter protein expression, and then induce pathological changes in zebrafish embryos, despite negligible physiological and developmental toxicity. This study investigated the single and combined developmental toxicity of fluoroquinolones (enrofloxacin [ENR] and ciprofloxacin [CIP]) (≤0.5 μM) and heavy metals (Cu and Cd) (≤0.5 μM) to zebrafish embryos, and molecular responses of zebrafish larvae upon exposure to the single pollutant (0.2 μM) or a binary metal-fluoroquinolone mixture (0.2 μM). In all single and mixture exposure groups, no developmental toxicity was observed, but oxidative stress, inflammation, and lipid depletion were found in zebrafish embryos, which was more severe in the mixture exposure groups than in the single exposure groups, probably due to increased metal bioaccumulation in the presence of ENR or CIP. Metabolomics analysis revealed the up-regulation of amino acids and down-regulation of fatty acids, corresponding to an active response to oxidative stress and the occurrence of inflammation. The up-regulation of antioxidase and immune proteins revealed by proteomics analysis further confirmed the occurrence of oxidative stress and inflammation. Furthermore, the KEGG pathway enrichment analysis showed a significant disturbance of pathways related to immunity and tumor, indicating the potential risk of tumorigenesis in zebrafish larvae. The findings provide molecular-level insights into the adverse effects of heavy metals and antibiotics (especially in chemical mixtures) on zebrafish embryos, and highlight the potential ecotoxicological risks of trace-level heavy metals and antibiotics in the environment.

Toxicity of microplastics and copper, alone or combined, in blackspot seabream (Pagellus bogaraveo) larvae

Plastics pose serious risks for fish productivity and a potential constraint for food security. Newly hatched blackspot seabream larvae were exposed to microplastics (MPs), copper (Cu, 10-810 µg/L) and their mixtures (Cu+MPs), during 3 and 9 days. Biochemical biomarkers and the expression of antioxidant and neurotoxicity-related genes were evaluated. In the 3-day exposure, catalase and glutathione-S-transferase activities decreased in MPs, Cu and Cu+MPs groups, followed by an increase of lipid peroxidation in the Cu270 and Cu270 +MPs exposed larvae. In the 9-day exposure, ROS levels increased in MPs and Cu30 groups, but no significant oxidative damage was observed, suggesting that the antioxidant system overcome the induced oxidative stress. However, the acetylcholinesterase transcript was downregulated in MPs, Cu and Cu10+MPs groups, indicating that MPs effects in cholinergic neurotransmission may arise after longer exposures. Overall, MPs and Cu can reduce survival, induce oxidative stress, lipid peroxidation, neurotoxicity, and impact negatively fish larvae fitness.

Transient Copper Exposure During Embryogenesis and Temperature Affect Developmental Rate, Survival, and Fin Regeneration in Japanese Medaka (Oryzias latipes)

Combined environmental stressors that an organism experiences can have both immediate and lasting consequences. In the present study, we exposed Japanese medaka (Oryzias latipes) embryos to sublethal copper sulfate (CuSO₄ ; 0, 10, and 100 ppb) in combination with different rearing temperatures (27, 30, and 33 °C) to assess acute and latent effects on development, growth, and regenerative capacity. Embryos exposed to CuSO₄ and/or higher temperatures hatched significantly earlier. At 4 months post-exposure, fish exposed to low levels of CuSO₄ during development had higher survival, whereas fish exposed to both 100 ppb CuSO₄ and 33 °C temperatures had significantly lower survival. In addition, a sex-specific effect of embryonic CuSO₄ exposure was observed as female mass decreased with increasing Cu dose. We also assessed caudal fin regenerative capabilities in both embryo-exposed fish at 4 months of age and adult medaka that were exposed to 0, 10, and 100 ppb CuSO₄ at room temperature during a 14-day trial. Whereas fin regeneration was unaffected by adult exposure to Cu, fish transiently exposed during embryogenesis displayed an initial increase in fin growth rate and an increased incidence of abnormal fin morphology following regrowth. Collectively, these data suggest that developmental Cu exposure has the potential to exert long-lasting impacts to organismal growth, survival, and function. Environ Toxicol Chem 2022;41:748-757. © 2021 SETAC.

Secondary PVC microplastics are more toxic than primary PVC microplastics to Oryzias melastigma embryos

Irregular-shaped and partially degraded secondary microplastics (SMP) account for the majority of MPs in marine environments, yet little is known about their effects on marine organisms. In this study, we investigated the embryotoxicity of polyvinyl chloride SMP and primary microplastics (PMP) to the marine medaka Oryzias melastigma. This study aimed to determine the physical impacts of MPs and, for the first time, elucidate the underlying mechanisms of physical toxicity. SMP shortened hatching time and induced higher teratogenic effects on larvae relative to PMP, indicating a higher toxicity from SMP. Physical damage from SMP to the chorion surface appears to be the main toxicity mechanism, caused by their irregular shape and reduced aggregation relative to PMP. In contrast, real-time changes in oxygen demonstrated that hypoxia caused by greater PMP adsorption to the chorion surface contributes to the toxicological responses of this material relative to SMP. Modulation of genes involved in hypoxia-response, cardiac development and hatching confirmed the toxicity mechanisms of PMP and SMP. The chemical contribution to observed toxicity was negligible, confirming impacts derived from physical toxicity. Our findings highlight the negative effects of environmentally relevant SMP on the marine ecosystems.

Tissue distribution and health risk of trace elements in East Asian finless porpoises

We investigated the tissue distribution, trophic transfer, and ecological risk of 13 trace elements in 26 East Asian finless porpoises (Neophocaena asiaeorientalis sunameri), an endangered species found in the Liaodong Bay and the north Yellow Sea. All the investigated trace elements were detected in the tissue and food web of the East Asian finless porpoises. The concentrations of the potentially toxic elements were 2.37 × 10^-5 - 754 mg kg^-1 dry weight (dw) in stranded porpoises and 0.01-159 mg kg^-1 dw in their food web. Tissue-specific distribution of the trace elements generally ranked as: liver > kidney > heart > lung > muscle. Zn was the dominant contaminant in the five investigated tissues. Significant positive correlations were found between body length or age and some trace elements, especially Cd. Adults (≥2 years old) presented higher concentrations of most of the trace elements than juveniles (<2 years old). Sex-dependent distribution of the trace elements was insignificant except for Mn, Ni, and Zn in muscle and renal tissue. As, Cu, Mn, Ni, Pb, and V biodiluted across the East Asian finless porpoise food web while Zn biomagnified. However, Hg, Cd, Co, Cr, Se, and Sn did not exhibit apparent trophic transfer trends. Overall, ecological risk assessment of trace elements in East Asian finless porpoises suggested that greater attention should be given to Hg, As, Cd, and Se.

Exposure to low environmental copper concentrations does not affect survival and development in Atlantic cod (Gadus morhua) early life stages

In this study we investigated potential impacts of Cu exposure at low, environmentally relevant, concentrations on early live stages of Atlantic cod (Gadus morhua). Cod embryos and larvae were exposed to 0.5 μg/L (low), 2 μg/L (medium), and 6 μg/L (high) Cu from 4 to 17 days post fertilisation (dpf). Hatching success, mortality, oxygen consumption, biometric traits, and malformations were determined. A dynamic energy budget (DEB) model was applied to identify potential impacts on bioenergetics. A positive correlation was found between Cu exposure concentrations and Cu body burden in eggs, but not in larvae. The tested concentrations did not increase mortality in neither embryos nor larvae, or larvae deformations. Further, the DEB model did not indicate effects of the tested Cu concentrations.

Development of an in vivo acute bioassay using the marine medaka Oryzias melastigma

To determine whether the marine medaka Oryzias melastigma is a suitable model organism for in vivo acute toxicity bioassay in seawater, we first determined whether there were differences in the concentrations of chemicals that were toxic to marine medaka (O. melastigma) and freshwater medaka (O. latipes). We performed in vivo acute toxicity bioassay with 3-chloroaniline, triclosan, 3,4-dichloroaniline, fenitrothion, and pyriproxyfen on larvae of both species. Although the concentrations of 3-chloroaniline and fenitrothion that were lethal to the larvae were identical for both species, the toxic concentrations of triclosan, 3,4-dichloroaniline, and pyriproxyfen were lower for O. melastigma than for O. latipes. We then used an in vivo acute toxicity bioassay to monitor the quality of coastal seawater in Akita, Japan. No lethal effects were observed in the harbor and canal in 2019. O. melastigma could be used to monitor the quality of seawater with salinities in the range 2-25. Our findings suggest that O. melastigma can be used as the test fish for in vivo acute toxicity bioassay intended for water quality monitoring.

Generation of a novel transgenic marine medaka (Oryzias melastigma) for highly sensitive detection of heavy metals in the environment

As typic priority pollutants in the marine environment, heavy metals can be accumulated in the human body leading to serious environmental and health problems. The metal regulatory elements (MREs) have been identified to be the main functional parts for the response to heavy metals. To develop a convenient biological monitoring tool for the detection of heavy metals in the oceans, we generated a transgenic marine medaka line Tg(OmMT: eGFP) with a truncated metallothionein promoter, which was only 193 bp and drove the expression of eGFP. After Tg(OmMT:eGFP) embryos were treated with four different heavy metals and different concentrations, the results showed that the expression level of eGFP was consistent with that of the endogenous mt. The transgenic embryos are very sensitive to Hg²⁺, and the fluorescence could be induced in the 0.0002 μM concentration, which is far lower than the primary water standard. The expression level of eGFP and mt showed a dose-dependent manner to heavy metals concentration. Taken together, the newly established marine medaka is a sensitive, efficient, and convenient tool for monitoring heavy metal pollution in the environment, especially seawater.

Developmental toxicity in marine medaka (Oryzias melastigma) embryos and larvae exposed to nickel

As an important trace metal, nickel (Ni) has been reported extensively in the studies on freshwater animals. However, the toxic effects of Ni on marine organisms are not clearly understood. Therefore, in order to investigate the toxic effects of Ni on the early development of marine fish, the marine medaka (Oryzias melastigma) embryos and larvae were immersed in 0.13-65.80 mg/L Ni solution. The results showed that Ni exposure changed the egg size and heart rate of the embryos, lowered the hatchability, increased the deformity rate, and shortened the total body length of newly hatched larvae. Besides, it was found that before organogenesis and post-hatching periods were the sensitive periods of embryos to Ni. The 25 d LC₅₀ value of embryos was 49.28 mg/L, and the 5 d LC₅₀ of larvae was 55.92 mg/L, indicating that the embryos were more sensitive to Ni than the larvae. Furthermore, the expressions of the metallothionein (MT) gene, the skeletal development-related gene (Cyp26b1) and the cardiac development-related genes (ATPase, smyd1, cox2 and bmp4) were determined, and the results showed that the expressions of ATPase and smyd1 were up-regulated, while MT, Cyp26b1 and cox2 were significantly down-regulated at 9 days post-fertilization (dpf). Overall, Ni exposure caused a significant toxic effect on the early development of the O. melastigma embryos and larvae. Our findings could provide an important supplement to the toxicity data of tropical Ni and provide a reference for the exploration of the molecular mechanisms of Ni toxicity.

Gender-dependent reproductive toxicity of copper metal-organic frameworks and attenuation by surface modification

Metal-organic frameworks (MOFs) as promising materials have been widely used in drug delivery, disease diagnosis and therapy; however, their effects on the reproductive system remain unknown, which hinders their further clinical applications. Here we show that repeated subcutaneous injections of copper MOFs (HKUST-1) induce higher toxicity into the male reproductive system relative to the female reproductive system, with disrupted seminiferous tubule histology, sperm generation disorder, irreversible sperm morphological abnormities and reduced pregnancy rate but only slight follicle dysfunction and pregnancy complications in female mice. Interestingly, the modification of HKUST-1 with folic acid attenuates the reproductive toxicity and even improves pregnancy and fetus development. This study confirms the gender-dependent toxicity of HKUST-1 to the reproductive system, and that folic acid modification could relieve the reproductive toxicity, thus providing us a deep understanding of reproductive toxicity of copper MOFs, and also a guideline and feasible way to improve the biocompatibility of copper MOFs for potential medical use.