Ecophysiological responses of juvenile seabass (Dicentrarchus labrax) exposed to increased temperature and dietary methylmercury

Insights into the potential enhanced cadmium toxicity in marine fish Centroprostis striata in the context of global warming

Cadmium (Cd2+), a pollutant from industrial activities, poses significant health risks to aquatic organisms, especially fish. Combined with global warming, its impact on marine ecosystems requires further investigation. This research examined the combined toxic effects of Cd2+ exposure and heat stress on the liver of black sea bass (Centropristis striata). Fish were subjected to varying Cd2+ concentrations (0, 0.83, and 6.4 mg/L) and temperatures (17 and 30 °C). Results indicated that heat stress markedly augmented Cd2+ bioaccumulation in the liver, exacerbating hepatotoxicity. Histological analysis revealed more severe liver damage under combined exposure than Cd2+ alone. Furthermore, a significant decrease in antioxidant enzyme activities (T-AOC, SOD, CAT, GSH) and a concomitant increase in oxidative stress marker (MDA) levels indicated enhanced oxidative stress. The co-exposure resulted in aberrant levels of apoptotic genes (e.g., P53, Bax etc.), disrupting the liver apoptotic process, as confirmed by TUNEL staining. Additionally, elevated TNF-α, IL-6, and HSP90 mRNA expression, coupled with decreased TGF-β levels, suggested an inflammatory response. These findings demonstrate that heat stress exacerbates Cd2+ toxicity in fish, highlighting a synergistic interaction between the two stressors. This research provides insights for managing heavy metal pollution under global warming.

Heat stress induces oxidative stress and weakens the immune system in catfish Clarias magur: Evidence from physiological, histological, and transcriptomic analyses

Climate change is unequivocal, causing a rise in the Earth's temperature, which ultimately impacts all ecosystems. However, aquatic ecosystems are most severely affected by rising temperatures resulting in huge losses to aquaculture industry. The present study investigated the oxidative stress, histopathological changes, and transcriptomic responses in a freshwater catfish Clarias magur subjected to acute heat stress. Fish were exposed to four different temperatures, i.e., 28, 30, 32, and 34 °C, for 96 h to assess their heat tolerance and adaptation behavior. Fish kept at 26 °C were considered the control group. Elevated levels of key antioxidative enzymes such as catalase, glutathione reductase, and superoxide dismutase, were recorded in vital organs (gills, kidney, liver, and rosette). High rates of lipid peroxidation were also observed in the gills, kidney, liver, and rosette. An analysis of the top 25 differentially expressed genes of the gill transcriptome revealed that 72 percent of the transcripts were represented by innate and adaptive immune response genes. Downregulation of BOLA class I and MHC class I molecules indicated impaired immunity whereas, upregulation of MHC class II beta chain and GTPase IMAP8 suggested a compensatory immune response. These findings were also supported by the observed histoarchitectural alterations, such as disintegration of the skin barrier, hepatic and nephrotic apoptosis, tissue hyperplasia, macrophage infiltration, and development of splenic granulomas. This study provides important insights into physiological and molecular mechanisms underlying acute heat stress responses. Understanding these mechanisms is important for developing mitigation strategies to improve the sustainability and resilience of commercially important catfish under continuously changing climatic conditions.

Biomarkers responses in the amphipod Tiburonella viscana exposed to the biocide DCOIT and CO2-induced ocean acidification

Anthropogenic carbon dioxide emissions (CO2) have led to climate change and marine acidification, with an estimated decrease in ocean surface pH of 0.3-0.4 units by the end of the current century. Chemical pollution also contributes to biodiversity loss in marine environments. This issue is particularly critical in areas under pressure from shipping activities, where the introduction of new antifouling system formulations poses a major threat to non-target species. The biocide DCOIT is the most widely used alternative to organotin compounds due to its rapid degradation in seawater. The toxicity of waterborne DCOIT to marine organisms has been documented, but sediment-bound effects are limited to apical responses and pH scenarios corresponding to current levels. In this study, we determine in a combined way, the toxicity of DCOIT under marine acidification scenarios assessing biomarker responses in the burrowing amphipod Tiburonella viscana as a parameter of sublethal effects in solid phase exposures. Environmental relevant concentrations of DCOIT caused inhibition of the enzyme glutathione S-transferases (GST), changed acetylcholinesterase-like activity (AChE), and increased DNA damage at pHs of 7.7 and 7.4. For lipid peroxidation (LPO), increased levels caused by DCOIT were found for both control (8.1) and intermediate (7.7) conditions of pH. Our data provides evidence of oxidative and genotoxic effects induced by DCOIT, with activation of detoxification and defense mechanisms in T. viscana. These results are important for ecological risk assessment and managing of antifouling paint biocides in multiple stressors scenarios.

Hot and toxic: Accumulation dynamics and ecotoxicological responses of mussel Mytilus galloprovincialis exposed to marine biotoxins during a marine heatwave

Climate change is increasing marine heatwaves (MHWs) frequency and severity worldwide. These extreme events often cause bivalves' mass mortality and facilitate the growth, proliferation and dispersion of toxin-producing microalgae blooms associated with threats to seafood safety. Yet, the interactive effects between MHW and uptake of marine biotoxins by biota are a novel topic still lacking thorough research, from both the ecotoxicological and seafood safety standpoints. This study assessed the effects of a MHW event on the accumulation/elimination dynamics of diarrhetic shellfish toxins in Mytilus galloprovincialis exposed to Prorocentrum lima and the ecotoxicological responses of mussels co-exposed to these two stressors. Results showed that acute exposure to +4 °C reduced toxins accumulation (-49 %) and elimination (-77 %) compared to control temperature. Moreover, exposure to MHW and toxins affected mussels' antioxidant activity, lipid and protein damage, and metabolism in a tissue-specific manner. These findings highlight that M. galloprovincialis can face higher vulnerability to toxins when MHW events strike.

Ecotoxicological responses of marine fish to the organophosphate flame-retardant tris (2-chloroisopropyl) phosphate (TCPP) dietary exposure: Juvenile gilthead seabream (Sparus aurata) as a case study

High Production Volume Chemicals (HPVCs) are contaminants that pose serious threats to aquatic environments and species that inhabit them, given their massive production and ubiquitous distribution across biological compartments. Among them, organophosphate esters (OPEs) are of particular concern, as they are widely used as plasticizers and flame-retardants, and linked to various forms of toxicity in marine organisms. In this study, we investigated the ecotoxicological response of juvenile gilthead seabream Sparus aurata to the OPE tris (2-chloroisopropyl) phosphate (TCPP) following chronic dietary exposure to three different concentrations (low, D1: 0.2 mg kg-1; ecologically relevant, D2: 2 mg kg-1; and high, D3: 10 mg kg-1). Different biomarkers indicative of antioxidant defence mechanisms (catalase, CAT, glutathione S-transferase, GST, activities), metabolism (citrate synthase, CS, lactate dehydrogenase, LDH, activities) and endocrine disruption (vitellogenin content, VTG), as well as cell (lipid peroxidation levels, LPO) and protein damage (ubiquitin content, UBI) were analyzed in liver and muscle to assess TCPP toxicity. High concentrations of TCPP affected S. aurata growth, but not overall fitness condition. Furthermore, metabolic disruption and severe oxidative damages were observed, regardless of exposure dose. VTG content significantly decreased after exposure to all TCPP dosages, indicating a possible masculinization effect. These findings provide new insights to the scientific knowledge on TCPP ecotoxicological attributes and impacts on marine ichthyofauna. In addition, our results confirm the relevance of conducting integrated multi-biomarker approaches to disclose the ecotoxicological effects of poorly studied chemical contaminants and, ultimately, implement wastewater treatment strategies and legislation to protect marine ecosystems from pollution.

Black sand nanoparticles and heat stress impacts the neurological and oxidative stress indices and splenic-renal histology of Clarias gariepinus

In Egypt, while many studies have focused on the radiometry and mineralogy of black sands, research on their effects on nearby aquatic organisms is rare. This study aimed to assess the combined effects of heat stress (HS) and black sand nanoparticles (BS-NPs) on renal function, antioxidant responses (TAC, SOD, CAT), neuro-stress indicators (AchE, cortisol), and to conduct histopathological investigations in the kidney and spleen tissues of African catfish Clarias gariepinus over a 15-day period to exposure to control, HS (32 °C), BS (6.4 g/kg diet) and HS + BS groups. The outcomes revealed that thermal stress alone showed no significant difference from the control. However, creatinine and uric acid levels were significantly higher in the BS-NPs and HS + BS-NPs groups (p < 0.001). Antioxidant markers (TAC, SOD, and CAT) were substantially reduced across all treated groups (0.05 ≥ p < 0.0001). AchE levels were significantly elevated in BS-NPs and HS + BS-NPs (p < 0.001), while cortisol levels were higher in these groups but not significantly different in HS. Degeneration and necrosis in the white and red pulps, scattered lymphocytes, and increased collagen fiber surrounding blood vessels and the lining of the ellipsoid structure were all evident in the spleen, along with the enlargement of the melanomacrophage centers with big granular, irregular, and brown pigments (hemosiderin). Our study, therefore, provides new insights into how heat stress, an abiotic environmental factor, influences the toxicity of black sand nanoparticles in catfish.

Toxicity of methylmercury in aquatic organisms and interaction with environmental factors and coexisting pollutants: A review

Mercury is a hazardous heavy metal that is distributed worldwide in aquatic ecosystems. Methylmercury (MeHg) poses significant toxicity risks to aquatic organisms, primarily through bioaccumulation and biomagnification, due to its strong affinity for protein thiol groups, which results in negative effects even at low concentrations. MeHg exposure can cause various physiological changes, oxidative stress, neurotoxicity, metabolic disorders, genetic damage, and immunotoxicity. To assess the risks of MeHg contamination in actual aquatic ecosystems, it is important to understand how MeHg interacts with environmental factors such as temperature, pH, dissolved organic matter, salinity, and other pollutants such as microplastics and organic compounds. Complex environmental conditions can cause potential toxicity, such as synergistic, antagonistic, and unchanged effects, of MeHg in aquatic organisms. This review focuses on demonstrating the toxic effects of single MeHg exposure and the interactive relationships between MeHg and surrounding environmental factors or pollutants on aquatic organisms. Our review also recommends further research on biological and molecular responses in aquatic organisms to better understand the potential toxicity of combinational exposure.

Asparagopsis taxiformis as a Novel Antioxidant Ingredient for Climate-Smart Aquaculture: Antioxidant, Metabolic and Digestive Modulation in Juvenile White Seabream (Diplodus sargus) Exposed to a Marine Heatwave

The increasing frequency and duration of marine heatwaves (MHWs) due to climate change pose severe threats to aquaculture, causing drastic physiological and growth impairments in farmed fish, undermining their resilience against additional environmental pressures. To ensure sustainable production that meets the global seafood demand and animal welfare standards, cost-effective and eco-friendly strategies are urgently needed. This study explored the efficacy of the red macroalga Asparagopsis taxiformis on juvenile white seabream Diplodus sargus reared under optimal conditions and upon exposure to a MHW. Fish were fed with four experimental diets (0%, 1.5%, 3% or 6% of dried powdered A. taxiformis) for a prophylactic period of 30 days (T30) and subsequently exposed to a Mediterranean category II MHW for 15 days (T53). Biometric data and samples were collected at T30, T53 and T61 (8 days post-MHW recovery), to assess performance indicators, biomarker responses and histopathological alterations. Results showed that A. taxiformis supplementation improved catalase and glutathione S-transferase activities and reduced lipid peroxidation promoted by the MHW, particularly in fish biofortified with 1.5% inclusion level. No histopathological alterations were observed after 30 days. Additionally, fish biofortified with 1.5% A. taxiformis exhibited increased citrate synthase activity and fish supplemented with 1.5% and 3% showed improved digestive enzyme activities (e.g., pepsin and trypsin activities). Overall, the present findings pointed to 1.5% inclusion as the optimal dosage for aquafeeds biofortification with A. taxiformis, and confirmed that this seaweed species is a promising cost-effective ingredient with functional properties and great potential for usage in a climate-smart context.

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

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

Ecotoxicological responses of juvenile Sparus aurata to BDE-99 and BPA exposure: A multi-biomarker approach integrating immune, endocrine and oxidative endpoints

Pentabromodiphenyl ether (BDE-99) and bisphenol A (BPA) are synthetic organic compounds present in several daily use products. Due to their physicochemical properties, they are ubiquitously present in aquatic ecosystems and considered highly persistent. Recent evidence has confirmed that both emerging compounds are toxic to humans and terrestrial mammals eliciting a wide range of detrimental effects at endocrine and immune levels. However, the ecotoxicological responses that they can trigger in vertebrate marine species have not yet been established. Hence, this study aimed to investigate the ecotoxicological responses of juvenile Sparus aurata upon chronic (28 days) dietary exposure to BDE-99 and BPA (alone and combined) following an integrated multi-biomarker approach that combined fitness indicators (Fulton's K and splenosomatic indexes) with endocrine [cortisol, 17β-estradiol (E2), 11-ketotestosterone (11-KT) concentrations] and immune (peroxidase and antiprotease activities) endpoints in fish plasma, and oxidative stress [superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) activities, and lipid peroxidation (LPO)] endpoints in the fish spleen. The mixture of BDE-99 and BPA yielded the highest IBR index value in both plasma and spleen biomarkers, therefore, suggesting that the effects of these compounds are more severe when they act together. Endocrine biomarkers were the most responsive in the three contaminated treatments. Fitness indicators were not affected by the individual nor the interactive effects of BDE-99 and BPA. These findings highlight the relevance of accounting for the interactive effects of emerging chemical contaminants and integrating responses associated with distinct biological pathways when investigating their impacts on marine life, as such a multi-biomarker approach provides a broader, more realistic and adequate perspective of challenges faced by fish in a contaminated environment.

Single and combined effects of increased temperature and methylmercury on different stages of the marine rotifer Brachionus plicatilis

Rapid, anthropogenic activity-induced global warming is a severe problem that not only raises water temperatures but also shifts aquatic environments by increasing the bioavailability of heavy metals (HMs), with potentially complicated effects on aquatic organisms, including small aquatic invertebrates. For this paper, we investigated the combined effects of temperature (23 and 28 °C) and methylmercury (MeHg) by measuring physiological changes, bioaccumulation, oxidative stress, antioxidants, and the mitogen-activated protein kinase signaling pathway in the marine rotifer Brachionus plicatilis. High temperature and MeHg adversely affected the survival rate, lifespan, and population of rotifers, and bioaccumulation, oxidative stress, and biochemical reactions depended on the developmental stage, with neonates showing higher susceptibility than adults. These findings demonstrate that increased temperature enhances potentially toxic effects from MeHg, and susceptibility differs with the developmental stage. This study provides a comprehensive understanding of the combined effects of elevated temperature and MeHg on rotifers. ENVIRONMENTAL IMPLICATION: Methylmercury (MeHg) is a widespread and harmful heavy metal that can induce lethal effects on aquatic organisms in even trace amounts. The toxicity of metals can vary depending on various environmental conditions. In particular, rising temperatures are considered a major factor affecting bioavailability and toxicity by changing the sensitivity of organisms. However, there are few studies on the combinational effects of high temperatures and MeHg on aquatic animals, especially invertebrates. Our research would contribute to understanding the actual responses of aquatic organisms to complex aquatic environments.

Effects of cadmium exposure on haemocyte immune function of clam Ruditapes philippinarum at different temperatures

Haemocytes are crucial for the immune defence of mollusks. It is important to explore the immune performance of haemocytes of mollusks under the stress of heavy metals with global warming. In order to study the effects of cadmium (Cd) exposure and temperature stress on the haemocyte immune function of clam Ruditapes philippinarum, clams were exposed to different Cd concentrations (0.05, 0.10 and 0.25 mg/L) at 20 °C, 25 °C and 30 °C respectively. Haemocyte mortality, reactive oxygen species (ROS) and superoxide dismutase (SOD) activity were measured at day 1, day 3, day 5 and day 7. The results showed that the changes of the three indexes were not obvious when exposed to 0.05 mg/L of Cd at 20 °C, while significant differences were observed with the increase of temperature, Cd concentration and exposure time. Under a condition of relative high temperature coupling with high concentration of Cd, the clams were significantly influenced, showing an obvious synergistic effect. Selected indexes reflect the clam's response to the combined stress of temperature and Cd. Moreover, R. philippinarum might be an ideal biological index species to the Cd pollution.

A Meta-analysis Reveals Global Change Stressors Potentially Aggravate Mercury Toxicity in Marine Biota

Growing evidence demonstrates that global change can modulate mercury (Hg) toxicity in marine organisms; however, the consensus on such effect is lacking. Here, we conducted a meta-analysis to evaluate the effects of global change stressors on Hg biotoxicity according to the IPCC projections (RCP 8.5) for 2100, including ocean acidification (-0.4 units), warming (+4 °C), and their combination (acidification-warming). The results indicated an overall aggravating effect (ln RRΔ = -0.219) of global change on Hg toxicity in marine organisms, while the effect varied with different stressors; namely, acidification potentially alleviates Hg biotoxicity (ln RRΔ = 0.117) while warming and acidification-warming have an aggravating effect (ln RRΔ = -0.328 and -0.097, respectively). Moreover, warming increases Hg toxicity in different trophic levels, i.e., primary producers (ln RRΔ = -0.198) < herbivores (ln RRΔ = -0.320) < carnivores (ln RRΔ = -0.379), implying increasing trends of Hg biomagnification through the food web. Notably, ocean hypoxia appears to boost Hg biotoxicity, although it was not considered in our meta-analysis because of the small sample size. Given the persistent global change and combined effects of these stressors in marine environments, multigeneration and multistressor research is urgently needed to fully disclose the impacts of global change on Hg pollution and its risk.

Effect of elevated temperature, sea water acidification, and phenanthrene on the expression of genes involved in the shell and pearl formation of economic pearl oyster (Pinctada radiata)

Our study aims to examine the effect of some stressors on the gene expression levels of shell matrix proteins in a pearl oyster. Oysters were exposed to the different combinations of the temperature, pH, and phenanthrene concentration is currently measured in the Persian Gulf and the predicted ocean warming and acidification for 28 days. The expression of all the studied genes was significantly downregulated. Time and temperature had the greatest effects on the decreases in n19 and n16 genes expression, respectively. Aspein and msi60 genes expression were highly influenced by pH. Pearlin was affected by double interaction temperature and phenanthrene. Moreover, a correlation was observed among the expression levels of studied genes. This study represents basic data on the relationship between mRNA transcription genes involved in the shell and pearl formation and climate changes in pollutant presence conditions and acclimatizing mechanism of the oyster to the future scenario as well.

Co-exposure of environmental contaminants with unfavorable temperature or humidity/moisture: Joint hazards and underlying mechanisms

In the context of global climate change, organisms in their natural habitats usually suffer from unfavorable climatic conditions together with environmental pollution. Temperature and humidity (or moisture) are two central climatic factors, while their relationships with the toxicity of contaminants are not well understood. This review provides a synthesis of existing knowledge on important interactions between contaminant toxicity and climatic conditions of unfavorable temperature, soil moisture, and air humidity. Both high temperature and low moisture can extensively pose severe combined hazards with organic pollutants, heavy metal ions, nanoparticles, or microplastics. There is more information on the combined effects on animalia than on other kingdoms. Prevalent mechanisms underlying their joint effects include the increased bioavailability and bioaccumulation of contaminants, modified biotransformation of contaminants, enhanced induction of oxidative stress, accelerated energy consumption, interference with cell membranes, and depletion of bodily fluids. However, the interactions of contaminants with low temperature or high humidity/moisture, particularly on plants and microorganisms, are relatively vague and need to be further revealed. This work emphasizes that the co-exposure of chemical and physical stressors results in detrimental effects generally greater than those caused by either stressor. It is necessary to take this into consideration in the ecological risk assessment of both environmental contamination and climate change.

Combined threats of climate change and contaminant exposure through the lens of bioenergetics

Organisms face energetic challenges of climate change in combination with suites of natural and anthropogenic stressors. In particular, chemical contaminant exposure has neurotoxic, endocrine-disrupting, and behavioral effects which may additively or interactively combine with challenges associated with climate change. We used a literature review across animal taxa and contaminant classes, but focused on Arctic endotherms and contaminants important in Arctic ecosystems, to demonstrate potential for interactive effects across five bioenergetic domains: (1) energy supply, (2) energy demand, (3) energy storage, (4) energy allocation tradeoffs, and (5) energy management strategies; and involving four climate change-sensitive environmental stressors: changes in resource availability, temperature, predation risk, and parasitism. Identified examples included relatively equal numbers of synergistic and antagonistic interactions. Synergies are often suggested to be particularly problematic, since they magnify biological effects. However, we emphasize that antagonistic effects on bioenergetic traits can be equally problematic, since they can reflect dampening of beneficial responses and result in negative synergistic effects on fitness. Our review also highlights that empirical demonstrations remain limited, especially in endotherms. Elucidating the nature of climate change-by-contaminant interactive effects on bioenergetic traits will build toward determining overall outcomes for energy balance and fitness. Progressing to determine critical species, life stages, and target areas in which transformative effects arise will aid in forecasting broad-scale bioenergetic outcomes under global change scenarios.

Review of warming and acidification effects to the ecotoxicity of pharmaceuticals on aquatic organisms in the era of climate change

An increase in the temperature and the acidification of the aquatic environment are among the many consequences of global warming. Climate change can also negatively affect aquatic organisms indirectly, by altering the toxicity of pollutants. Models of climate change impacts on the distribution, fate and ecotoxicity of persistent pollutants are now available. For pharmaceuticals, however, as new environmental pollutants, there are no predictions on this issue. Therefore, this paper organizes the existing knowledge on the effects of temperature, pH and both stressors combined on the toxicity of pharmaceuticals on aquatic organisms. Besides lethal toxicity, the molecular, physiological and behavioral biomarkers of sub-lethal stress were also assessed. Both acute and chronic toxicity, as well as bioaccumulation, were found to be affected. The direction and magnitude of these changes depend on the specific pharmaceutical, as well as the organism and conditions involved. Unfortunately, the response of organisms was enhanced by combined stressors. We compare the findings with those known for persistent organic pollutants, for which the pH has a relatively low effect on toxicity. The acid-base constant of molecules, as assumed, have an effect on the toxicity change with pH modulation. Studies with bivalves have been were overrepresented, while too little attention was paid to producers. Furthermore, the limited number of pharmaceuticals have been tested, and metabolites skipped altogether. Generally, the effects of warming and acidification were rather indicated than explored, and much more attention needs to be given to the ecotoxicology of pharmaceuticals in climate change conditions.

Aquaponics as a Promising Strategy to Mitigate Impacts of Climate Change on Rainbow Trout Culture

Simple Summary

Climate change and overexploitation of natural resources drive the need for innovative food production within a sustainability corridor. Aquaponics, combining the technology of recirculation aquaculture systems (RAS) and hydroponics in a closed-loop network, could contribute to addressing these problems. Aquaponic systems have lower freshwater demands than agriculture, greater land use efficiency, and decreased environmental impact combined with higher fish productivity. Rainbow trout is one of the major freshwater fish cultured worldwide, which, however, has not yet been commercially developed in aquaponics. Nevertheless, research conducted so far indicates that the trout species represents a good candidate for aquaponics.

Abstract

The impact of climate change on both terrestrial and aquatic ecosystems tends to become more progressively pronounced and devastating over the years. The sector of aquaculture is severely affected by natural abiotic factors, on account of climate change, that lead to various undesirable phenomena, including aquatic species mortalities and decreased productivity owing to oxidative and thermal stress of the reared organisms. Novel innovative technologies, such as aquaponics that are based on the co-cultivation of freshwater fish with plants in a sustainable manner under the context of controlled abiotic factors, represent a promising tool for mitigating the effect of climate change on reared fish. The rainbow trout (Oncorhynchus mykiss) constitutes one of the major freshwater-reared fish species, contributing to the national economies of numerous countries, and more specifically, to regional development, supporting mountainous areas of low productivity. However, it is highly vulnerable to climate change effects, mainly due to the concrete raceways, in which it is reared, that are constructed on the flow-through of rivers and are, therefore, dependent on water’s physical properties. The current review study evaluates the suitability, progress, and challenges of developing innovative and sustainable aquaponic systems to rear rainbow trout in combination with the cultivation of plants. Although not commercially developed to a great extent yet, research has shown that the rainbow trout is a valuable experimental model for aquaponics that may be also commercially exploited in the future. In particular, abiotic factors required in rainbow trout farming along, with the high protein proportion required in the ratios due to the strict carnivorous feeding behavior, result in high nitrate production that can be utilized by plants as a source of nitrogen in an aquaponic system. Intensive farming of rainbow trout in aquaponic systems can be controlled using digital monitoring of the system parameters, mitigating the obstacles originating from extreme temperature fluctuations.

Investigation on Immune-Related Protein (Heat Shock Proteins and Metallothionein) Gene Expression Changes and Liver Histopathology in Cadmium-Stressed Fish

Heat shock proteins (HSP) are highly conserved in their structure and released in case of stress. Increased metallothionein (MT) synthesis is associated with increased capacity for binding heavy metals. Healthy juveniles of grass carp were exposed to sublethal dose (1.495 mg L⁻¹) of cadmium for 28 days. Simultaneously, a control group was also run to compare difference of total RNA expression levels in cadmium-treated and control groups. The cadmium levels in the tissues of treated fish recorded were 1.78 ± 0.10 mg L⁻¹, 1.60 ± 0.04 mg L⁻¹, and 2.00 ± 0.05 mg L⁻¹, respectively. Several histological alterations including edema, hemorrhage, dilated sinusoids, hypertrophy, hyperplasia, congestion of central vein, and nuclear alterations were observed in cadmium-exposed fish. Stress gene (metallothionein and heat shock proteins) mRNA transcription levels were studied by mRNA extraction and cDNA preparation by using PCR. The expression level of heat shock protein gene was higher as compared to metallothionein and beta-2-microglobulin gene after cadmium exposure. This study reports various stress-related immune-responsive changes of immune proteins, heat shock proteins, metallothionein, and histopathological changes in fish due to cadmium toxicity that make the fish immunocompromised which may be considered as the biomarkers of cadmium toxicity in other experimental species.

Assessment of deep eutectic solvents toxicity in zebrafish (Danio rerio)

Deep Eutectic Systems (DES) have emerged as a "green alternative" to organic solvents and have been coined as biocompatible and biodegradable. However, the number of studies concerning the real biodegradability and biocompatibility are scarce. Thus, to study the toxicity of certain DES, two different approaches were used: i) zebrafish exposure via water, where the system (DES) was tested at potentially realistic environmental concentrations and ii) via intraperitoneal injection, where the system was tested in different concentrations, relevant to the pharmaceutical industry. These studies were performed using zebrafish, a standardized animal model often used in biomedicine and toxicological assays. The results show low toxicity according to tested concentrations (up to 73.47 μM), when the system CA:T:W, with a 2:1:3 molar ratio, was tested through exposure via water and also in the intraperitoneal injection tests with concentrations up to 6000 μM. The activity of different enzymes involved in antioxidant pathways (glutathione S-transferase, catalase, glutathione peroxidase), the total antioxidant capacity (TAC) and lipoperoxidation (MDA content) were determined suggesting low toxicity of the tested system (DES). The promising results herein presented show that DES present the potential to be used as the new class of green solvents, not only for use in the pharmaceutical industry, but also in cosmetic and chemical engineering processes without causing negative impact on living organisms.

Response mechanism of gut microbiome and metabolism of European seabass (Dicentrarchus labrax) to temperature stress

In animals, the gut microbiome is vital to growth, and changes in the composition of these microbial communities may affect growth and adaptability to the environment. Temperature is another important factor that influences the healthy growth of animals. To date, the mechanism by which juvenile European seabass (Dicentrarchus labrax) and their symbiotic flora adapt to changes in environmental temperature is not well understood. Therefore, we evaluated the effect of temperature on the gut microbiota and metabolism of European seabass juveniles. We used 16S rRNA gene amplicon sequencing and non-targeted liquid chromatography with tandem mass spectrometry (LC-MS/MS)-based metabolomics to study the gut microbes of European seabass after 60 days of rearing of water temperature at 10 °C (T1), 15 °C (T2) and 20 °C (T3). At the phylum level, the abundance of the gut microbiota did not differ significantly among the three groups after 60 days of cultivation. At the genus level, however, the abundance of Faecalibacterium, Filifactor, Butyricicoccus, and Erysipelotrichaceae UCG-006 in the intestines differed significantly among the temperature groups. Compared with T2, the relative abundance of Filifactor in T1 was significantly increased, while Faecalibacterium was significantly decreased, while the relative abundance of Butyricicoccus and Erysipelotrichaceae UCG-006 in T3 was significantly increased. The LC-MS/MS analysis revealed 107 metabolites in the 10 °C group and 68 metabolites in the 20 °C group that differed significantly from those in the intestines of fish in the 15 °C control group. These metabolites are closely related to several metabolic pathways, including amino acid metabolism, glucose and lipid metabolism, and the tricarboxylic acid cycle. Correlation analysis of the Intestine microbiota, metabolic pathways, and metabolites identified metabolic pathways and metabolites that were strongly related to the observed significant differences in the microbiome among the temperature groups. These results show that temperature can induce significant changes in the gut microbiota and metabolism of European seabass juveniles, and that significant changes in metabolites may be mediated through the interaction of the microbiome and metabolic pathways.

How efficient is graphene-based nanocomposite to adsorb Hg from seawater. A laboratory assay to assess the toxicological impacts induced by remediated water towards marine bivalves

Advanced investigations on the use of graphene based nanomaterials have highlighted the capacity of these materials for wastewater treatment. Research on this topic revealed the efficiency of the nanocomposite synthetized by graphene oxide functionalized with polyethyleneimine (GO-PEI) to adsorb mercury (Hg) from contaminated seawater. However, information on the environmental risks associated with these approaches are still lacking. The focus of this study was to evaluate the effects of Hg in contaminated seawater and seawater remediated by GO-PEI, using the species Ruditapes philippinarum, maintained at two different warming scenarios: control (17 °C) and increased (22 °C) temperatures. The results obtained showed that organisms exposed to non-contaminated and remediated seawaters at control temperature presented similar biological patterns, with no considerable differences expressed in terms of biochemical and histopathological alterations. Moreover, the present findings revealed increased toxicological effects in clams under remediated seawater at 22 °C in comparison to those subjected to the equivalent treatment at 17 °C. These results confirm the capability of GO-PEI to adsorb Hg from water with no noticeable toxic effects, although temperature could alter the responses of mussels to remediated seawater. These materials seem to be a promise eco-friendly approach to remediate wastewater, with low toxicity evidenced by remediated seawater and high regenerative capacity of this nanomaterial, keeping its high removal performance after successive sorption-desorption cycles.

Extreme winter cold-induced osmoregulatory, metabolic, and physiological responses in European seabass (Dicentrarchus labrax) acclimatized at different salinities

Despite climate-change challenges, for most aquaculture species, physiological responses to different salinities during ambient extreme cold events remain unknown. Here, European seabass acclimatized at 3, 6, 12, and 30 PSU were subjected to 20 days of an ambient extreme winter cold event (8 °C), and monitored for growth and physiological performance. Growth performance decreased significantly (p < 0.05) in fish exposed at 3 and 30 PSU compared to 6 and 12 PSU. During cold stress exposure, serum Na+, Cl-, and K+ concentrations were significantly (p < 0.05) increased in fish exposed at 30 PSU. Serum cortisol, glucose, and blood urea nitrogen (BUN) were increased significantly (p < 0.05) in fish exposed at 3 and 30 PSU. In contrast, opposite trends were observed for serum protein, lactate, and triglycerides content during cold exposure. Transaminase activities [glutamic-pyruvate transaminase (GPT), glutamic oxaloacetic transaminase (GOT), lactic acid dehydrogenase (LDH), gamma-glutamyl-transaminase (γGGT)] were significantly higher in fish exposed at 3 and 30 PSU on days 10 and 20. The abundance of heat shock protein 70 (HSP70), tumor necrosis factor-α (TNF-α), cystic fibrosis transmembrane conductance (CFTR) were significantly (p < 0.05) increased in fish exposed at 3 and 30 PSU during cold shock exposure. In contrast, insulin-like growth factor 1 (Igf1) expression was significantly lower in fish exposed at 3 and 30 PSU. Whereas, on day 20, Na+/K+ ATPase α1 and Na+/K+/Cl- cotransporter-1 (NKCC1) were significantly upregulated in fish exposed at 30 PSU, followed by 12, 6, and 3 PSU. Results demonstrated that ambient extreme winter cold events induce metabolic and physiological stress responses and provide a conceivable mechanism by which growth and physiological fitness are limited at cold thermal events. However, during ambient extreme cold (8 °C) exposure, European seabass exhibited better physiological fitness at 12 and 6 PSU water, providing possible insight into future aquaculture management options.

Metabolomics analysis of the effects of temperature on the growth and development of juvenile European seabass (Dicentrarchus labrax)

Temperature variations have significant impacts on the growth and development of fish. In this study, the effects of temperature on the growth and development of European seabass (Dicentrarchus labrax) were investigated using ultra-performance liquid chromatography-tandem mass spectrometry-based metabolomics. Three groups of fish were exposed to various temperatures for 60 days: T1-E (10 °C), T2-E (15 °C), and T3-E (20 °C). Afterward, the temperature of all groups was increased to 20 °C and maintained for 62 days (T1-S, T2-S, T3-S). The livers were extracted for subsequent analysis. In the first stage of the experiment, the growth rate was highest in the T3-E group, followed by the T1-E and T2-E groups. The following metabolites identified by comparative analysis were found to be elevated: L-thyroxine, cysteamine, uridine diphosphate (UDP)-glucose, α-ketoglutaric acid, carbamoyl phosphate, and guanidine acetic acid of the T1-E group. Pathway analysis of the altered metabolites suggested changes in glucose metabolism, arginine and proline metabolism, the tricarboxylic acid cycle, the ornithine cycle, histidine metabolism, and taurine metabolism, which were involved with growth and development. Meanwhile, partial compensatory growth was observed in fish in the T1-S and T2-S groups. Metabolites identified as potential markers of growth included L-cysteine, taurocholic acid, UDP-glucose, and L-thyroxine. The significantly changed metabolic pathways were cysteine and methionine metabolism, bile secretion, tyrosine metabolism, and hypotaurine metabolism. We screened out the marker metabolites and metabolic pathway could provide important insights into the potential mechanisms of temperature affects the growth and development of European seabass. All in all, our research can provide theoretical basis and technical guidance for efficiently culturing European seabass.

A Multi-Biomarker Approach in European Sea Bass Exposed to Dynamic Temperature Changes under Dietary Supplementation with Origanum vulgare Essential Oil

A feeding trial for 150 days was carried out to evaluate the cross-effects between oregano essential oil (EO) dietary supplementation and dynamic temperature change in sea bass. Under exposure to rising temperature (13-25 °C), fish were fed with a control diet (CD) and two experimental diets supplemented with 100 (D100) and 200 ppm (D200) of EO. Feed inclusion of EO promoted the activity of antioxidant enzymes in sea bass exposed to increasing temperature. Consistently with the temperature rise, TBARS concentrations increased in CD and D200 groups, whereas were almost stable in D100. Trend of blood glucose in fish fed on CD was likely affected by glycogenolysis and gluconeogenesis. Similarly, the depletion of triglycerides and cholesterol in fish fed on CD likely supported the energy cost of gluconeogenesis. On the other hand, the reduction of glucose, triglycerides, and cholesterol in D100 and D200 was mainly attributable to the hypoglycemic and hypolipidemic effects of EO. The higher levels of serum protein observed in D100 and D200 groups were also associated to a reduced thermal stress compared to CD. EO dietary supplementation may be a promising strategy to alleviate the negative effects of temperature shift on sea bass physiological and oxidative state.

Effects of methylmercury on the early life stages of an estuarine forage fish using two different dietary sources

Marine fish accumulate methylmercury (MeHg) to elevated concentrations, often higher than in freshwater systems. As a neurotoxic compound, high MeHg tissue concentrations could affect fish behavior which in turn could affect their populations. We examined the sublethal effects of MeHg on larvae of the Sheepshead minnow (Cyprinodon variegatus), an estuarine fish, using artificial or natural diets with varying MeHg concentrations (0-4.8 ppm). Larvae were fed control and MeHg-contaminated diets at low or normal (10% of their body mass) daily food rations from 7 to 29 days when they reached juvenile stage. Growth, respiration, swimming activity and prey capture ability were assessed. Food ration affected Hg toxicity in our study. Natural diets containing 3.2 ppm MeHg had no impacts on growth and swimming in fish that were fed normal food rations but depressed growth and swimming at low food rations. MeHg toxicity did not differ between artificial and natural foods, however fish accumulated more MeHg from the former. Artificial food containing 4.8 ppm MeHg only affected prey capture after 21 days of exposure. Sheepshead minnows, a forage fish species occupying a low trophic level in coastal waters, can be MeHg tolerant, especially when food is abundant, and can serve as an enriched Hg source for higher trophic level predators.

What metabolic, osmotic and molecular stress responses tell us about extreme ambient heatwave impacts in fish at low salinities: The case of European seabass, Dicentrarchus labrax

Unprecedented shifts in temperature and precipitation patterns in recent decades place multiple abiotic stressors on the fish. In teleosts, metabolic, osmoregulatory, and molecular potential as tolerance responses to extreme ambient heatwave events at different salinities are poorly understood. The study was performed to evaluate the physio-biochemical stress responses and acclimation potential of European seabass, Dicentrarchus labrax maintained at four different salinities followed by an extreme ambient heatwave exposure. Fish were kept at 32, 12, 6, and 2 psu for 35 days followed by a simulated extreme ambient heatwave (33 °C) exposure for 10 days. Fish growth performances, physio-biochemical and molecular responses were recorded. Fish acclimated at 32 and 2 psu exhibited significantly (p < 0.05) decreased growth performance. Serum [Na⁺] and [Cl^-] ions were significantly lowered (p < 0.05) in 32 psu fish on day 10 of heatwave exposure. While serum glucose, triglycerides, and protein tended to decrease during the extreme ambient heatwave exposure, lactate content increased significantly (p < 0.05) in 32 psu fish on day 10. In 32 and 2 psu fish, serum metabolic enzymes, and cortisol levels increased significantly (p < 0.05) during the extreme heatwave exposure. On days 5 and 10, HSP70 mRNA was significantly (p < 0.05) upregulated in kidneys and gills of 32 and 2 psu fish, while Igf1 showed downregulation. In gills of 2 psu fish, ATPase Na⁺/K⁺-α1 and NKCC1 expression decreased significantly (p < 0.05) in 2 psu, in contrast, significant upregulation was observed at 32 psu fish during extreme ambient heatwave exposure. On days 5 and 10, cystic fibrosis transmembrane conductance (CFTR) upregulation was significantly lower (p < 0.05) in 32 and 2 psu fish. Results suggest that European seabass held at 12 and 6 psu water fare better physiological fitness during the tested extreme ambient heatwave event (33 °C), providing possible insights into options for future aquaculture management in a warming environment.

Multi-organ characterisation of B-esterases in the European sea bass (Dicentrarchus labrax): Effects of the insecticide fipronil at two temperatures

In fish, the study of cholinesterases (ChEs) and carboxylesterases (CEs), apart from their involvement in neural activity and xenobiotic metabolism, respectively, requires to be further explored. The European sea bass (Dicentrarchus labrax) was the fish model used to characterise B-esterases in several matrices and organs, as well as to assess the impacts of the insecticide fipronil at two temperatures: the natural temperature at the time of sampling (13 °C) and at 16 °C (based on climate change-related predictions for the Mediterranean region). Fipronil exerts harmful effects in non-target species; however, some countries are reluctant to implement regulations without additional evidence on their toxicity. A comprehensive study was performed in fish pre-acclimated to the two targeted temperatures for 15 days. B-esterases were evaluated in multiple samples after 7 and 14 day exposures to fipronil in feed (dose of 10 mg/kg) and after a 7-day depurative period. Based on hydrolysis rates, results showed that CEs were measurable in all matrices while ChEs were more abundant in muscle and, particularly, acetylcholinesterase (AChE) in the brain. A + 3 °C increase in temperature had little influence on B-esterase activity; however, fipronil caused a significant increase in brain AChE (1.5-fold) and CE (3-fold) activities. Other matrices and organs also experienced alterations in their B-esterase activities that could compromise their physiological functions.

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

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

Effects of extreme ambient temperature in European seabass, Dicentrarchus labrax acclimated at different salinities: Growth performance, metabolic and molecular stress responses

Extreme weather events are becoming more intense and frequent as a result of climate change. The modulation of hemato-physiological potential as a compensatory response to extreme warm events combined with different salinities is poorly understood. This study aimed to assess the hemato-physiological and molecular response of European seabass, Dicentrarchus labrax exposed to extreme warm temperature (33 °C) after prior acclimatization at 32 psu, 12 psu, 6 psu, and 2 psu water. Fish were acclimated to 32 psu, 12 psu, 6 psu, and 2 psu followed by 10 days extreme warm (33 °C) exposure. Along with growth performance and survival, hemato-physiological response and molecular response of fish were recorded. Fish held at 32 psu and 2 psu exhibited significantly lower growth performance and survival than those at 12 psu and 6 psu (p < 0.05). Red blood cells (RBC), hematocrit, and hemoglobin content were significantly decreased, while white blood cells (WBC), erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) were found to increase significantly in 32 psu and 2 psu fish (p < 0.05). Plasma lactate was found to increase significantly in 32 psu fish on day 10 (p < 0.05). Activities of glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and TNF-α expression increased significantly in 32 psu and 2 psu fish (p < 0.05). Most of the repeated measured parameters indicated limited acclimation capacity during the extreme warm exposure at all four salinity groups. However, overall results indicate that European seabass acclimatized at 12 psu and 6 psu salinities, can cope better during extreme warm exposure (33 °C).

Effects of thermal stress-induced lead (Pb) toxicity on apoptotic cell death, inflammatory response, oxidative defense, and DNA methylation in zebrafish (Danio rerio) embryos

Lead (Pb) is a toxic environmental pollutant that is frequently present in effluents from urban, mining, and industrial sources. The combinatorial effects of heavy metal exposure and temperature in aquatic organisms have received considerable attention as heat stress occurs simultaneously in conjunction with several contaminants in a natural environment. In this study, we examined the potential effects of Pb exposure in conditions of thermal stress (34 °C) in zebrafish (Danio rerio) embryos. Thermal stress at 34 °C induced a dramatic decrease in the survival rate, although exposure to Pb at 26 °C decreased the survival rate of the embryos. Malformations, such as the curved body shape, were increased in response to exposure to a combination of Pb and heat stress. The combination of Pb and heat stress also caused a decrease in the heart rate. Moreover, Pb and high-temperature exposure induced the upregulation of SOD, CAT, TNF-α, IL-1β, p53, and BAX transcripts, and downregulation of Dnmt1 and Dnmt3b transcripts. Thermal stress enhanced transcriptional responses of eight indicator genes following Pb toxicity. The induction of cell death in response to combined exposures was also confirmed in the body of zebrafish by fluorescence intensity image analysis. These data indicated that thermal stress enhanced the poisonous effects of Pb exposure on antioxidant defense, inflammation, and apoptotic mechanisms. Transcriptional inhibition of DNA methylation-related genes might serve as a crucial factor contributing to the possibility of epigenetic adaptation by altering combined stress. We suggest that a careful evaluation of the potential effects of climate change (especially temperature) should be considered when investigating the toxic levels of metal pollution, such as Pb, in an aquatic environment.

Impacts of nanoplastics on bivalve: Fluorescence tracing of organ accumulation, oxidative stress and damage

The outcomes of this research offer novel insights into the toxic effects of nanoparticles (i.e., nanoplastics or other nanomaterials) on the benthos. Herein, this study aimed to evaluate the accumulation pathway, distribution characteristics and potential biotoxicity of polystyrene nanoplastics in C. fluminea. The results revealed that nanoplastics could accumulate in the mantle through adherence, in the visceral mass through ingestion and in the gill through respiration. The gill, intestine and stomach were the main accumulation organs for nanoplastics. The aggregation of nanoplastics was observed in C. fluminea, which may exacerbate their biotoxicity. Moreover, oxidative stress was observed in the visceral mass, gill and mantle. Liver damage, neurotoxicity and intestinal inflammation were caused by imbalance in the antioxidation system. Analysis of IBR values showed that the visceral mass had a more effective response to oxidative stress than the gill and mantle after exposure to nanoplastics.

Effects of combined stressors to cadmium and high temperature on antioxidant defense, apoptotic cell death, and DNA methylation in zebrafish (Danio rerio) embryos

Fish are frequently affected by environmental stressors, such as temperature changes and heavy metal exposure, in aquatic ecosystems. In this study, we evaluated the combined effects of cadmium (Cd) toxicity and temperature (rearing temperature of 26 °C and heat stress at 34 °C) on zebrafish (Danio rerio) embryos. The survival and heart rates of zebrafish embryos decreased at relatively high Cd concentrations of 0.07 and 0.1 mg L^-1. Abnormal morphology was induced by exposure to a combination of Cd toxicity and heat stress. The yolk sac edema size was not significantly different between the control- and Cd-treated groups. Cd exposure induced reactive oxygen species (ROS) production and cell death in the live zebrafish. High temperature (34 °C) triggered Cd-induced cell death and intracellular ROS production to a greater extent than the rearing temperature of 26 °C. Transcriptional levels of six genes-CAT, SOD, p53, BAX, Dnmt1, and Dnmt3b-were investigated. The mRNA expression of CAT and SOD, molecular indicators of oxidative stress, was increased significantly at 34 °C after Cd exposure. The mRNA expression of CAT was more sensitive to temperature than that of SOD in Cd-treated zebrafish. p53 and BAX, apoptosis-related genes, were upregulated upon combined exposure to high temperature and Cd. In addition, at 34 °C, the expression of Dnmt1 and Dnmt3b transcripts, markers of DNA methylation, was increased upon exposure of zebrafish to all concentrations of Cd. Overall, these results suggest that high temperature facilitates the potential role of Cd toxicity in the transcriptional regulation of genes involved in the antioxidant system, apoptosis, and DNA methylation.

Mercury in Juvenile Solea senegalensis: Linking Bioaccumulation, Seafood Safety, and Neuro-Oxidative Responses under Climate Change-Related Stressors

Mercury (Hg) is globally recognized as a persistent chemical contaminant that accumulates in marine biota, thus constituting an ecological hazard, as well as a health risk to seafood consumers. Climate change-related stressors may influence the bioaccumulation, detoxification, and toxicity of chemical contaminants, such as Hg. Yet, the potential interactions between environmental stressors and contaminants, as well as their impacts on marine organisms and seafood safety, are still unclear. Hence, the aim of this work was to assess the bioaccumulation of Hg and neuro-oxidative responses on the commercial flat fish species Solea senegalensis (muscle, liver, and brain) co-exposed to dietary Hg in its most toxic form (i.e., MeHg), seawater warming (ΔT°C = +4 °C), and acidification (pCO2 = +1000 µatm, equivalent to ΔpH = −0.4 units). In general, fish liver exhibited the highest Hg concentration, followed by brain and muscle. Warming enhanced Hg bioaccumulation, whereas acidification decreased this element’s levels. Neuro-oxidative responses to stressors were affected by both climate change-related stressors and Hg dietary exposure. Hazard quotient (HQ) estimations evidenced that human exposure to Hg through the consumption of fish species may be aggravated in tomorrow’s ocean, thus raising concerns from the seafood safety perspective.

Multibiomarker approach to fipronil exposure in the fish Dicentrarchus labrax under two temperature regimes

Fipronil is a phenylpyrazole insecticide widely used to control pests in agriculture even though evidence of harmful side effects in non-target species has been reported. A comprehensive study on the effects of dietary administration of Regent®800WG (80 % fipronil) in European sea bass juveniles was carried out under two temperature regimes: a) natural conditions, and b) 3 °C above the natural temperature (an increase predicted for the NW Mediterranean by the end of this century). Fipronil was added to the fish food (10 mg fipronil /Kg feed) and the effects were studied at several time points including right before administration, 7 and 14 days after daily fipronil feed and one-week after the insecticide withdrawal from the diet (depuration period). A wide array of physiological and metabolic biomarkers including feeding rate, general condition indices, plasma and epidermal mucus metabolites, immune response, osmoregulation, detoxification and oxidative-stress markers and digestive enzymes were assessed. General linear models and principal component analyses indicated that regardless of water temperature, fipronil resulted in a significant alteration of several of the above listed biomarkers. Among them, glucose and lactate levels increased in plasma and decreased in epidermal mucus as indicators of a stress response. Similarly, a depletion in catalase activity and higher lipid peroxidation in liver of fipronil-exposed fish were also indicative of an oxidative-stress condition. Fipronil induced a time dependent inhibition of Cytochrome P450-related activities and an increase of phase II glutathione-S-transferase. Moreover, fipronil administration was able to reduce the hypo-osmoregulatory capability as shown by the increase of plasmatic osmolality and altered several digestive enzymes including trypsin, lipase, alpha amylase and maltase. Finally, analyses in bile and muscle confirmed the rapid clearance of fipronil but the persistence of the metabolite fipronil-sulfone in bile even after the 7-day depuration period. Altogether, the results reveal a notable impact of this compound on the physiological condition of the European sea bass. The results should be considered in future environmental risk assessment studies since fipronil could be hazardous to fish species, particularly those inhabiting estuarine ecosystems exposed to the discharge of agriculture runoffs where this pesticide is mainly used.

Simultaneous exposure to vinylcyclohexene and methylmercury in Drosophila melanogaster: biochemical and molecular analyses

Background

Exposure to vinylcyclohexene (VCH) and methylmercury (MeHg⁺) can induce oxidative stress and gene modulation. Several studies have been evaluating the effects of VCH and MeHg⁺, but little is known about interactive effects between them. This work aimed to assess the exposure and co-exposure effects of MeHg⁺ and VCH on oxidative stress and gene modulation in Drosophila melanogaster.

Methods

Reactive species production, glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities were evaluated after exposure and co-exposure to VCH (1 mM) and MeHg⁺ (0.2 mM) for one or three days in the head and body (thorax and abdomen) of flies. The expression of genes related to redox state and inflammatory response was evaluated after exposure and co-exposure to VCH and MeHg⁺ for three days.

Results

Survival decreased only in flies co-exposed to VCH and MeHg⁺ for three days. All treatments increased total reactive species production after one day of exposure. However, no significant changes were observed in the head after three days of exposure. One day of exposure to VCH caused an increase in the head GST activity, whereas MeHg⁺ induced an increase after three days of exposure. Regarding the body, all treatments increased GST activity after one day of exposure, but only the flies exposed to MeHg⁺ presented an increase in GST activity after three days of exposure. Treatments did not alter AChE activity in the head. As for gene expression, there was a significant increase in the Relish transcription factor gene in the flies’ body, but Nrf2, Keap1, Jafrac1, TrxR1, and NF-κβ were not altered.

Conclusion

The results suggest that exposure to VCH and MeHg⁺ induce oxidative stress and activation of an inflammatory response in fruit flies.

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

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

Effects of temperature, salinity, and sediment organic carbon on methylmercury bioaccumulation in an estuarine amphipod

Mercury (Hg) is a global contaminant that poses a human health risk in its organic form, methylmercury (MeHg), through consumption of fish and fishery products. Bioaccumulation of Hg in the aquatic environment is controlled by a number of factors expected to be altered by climate change. We examined the individual and combined effects of temperature, sediment organic carbon, and salinity on the bioaccumulation of MeHg in an estuarine amphipod, Leptocheirus plumulosus, when exposed to sediment from two locations in the Gulf of Maine (Kittery and Bass Harbor) that contained different levels of MeHg and organic carbon. Higher temperatures and lower organic carbon levels individually increased uptake of MeHg by L. plumulosus as measured by the biota-sediment accumulation factor (BSAF), while the effect of salinity on BSAF differed by sediment source. Multi-factor statistical modeling using all data revealed a significant interaction between temperature and organic carbon for both sediments, in which increased temperature had a negative effect on BSAF at the lowest carbon levels and a positive effect at higher levels. Our results suggest that increased temperature and carbon loading, of a magnitude expected as a result from climate change, could be associated with a net decrease in amphipod BSAF of 50 to 71%, depending on sediment characteristics. While these are only first-order projections, our results indicate that the future fate of MeHg in marine food webs is likely to depend on a number of factors beyond Hg loading.

Paralytic Shellfish Toxins and Ocean Warming: Bioaccumulation and Ecotoxicological Responses in Juvenile Gilthead Seabream (Sparus aurata)

Warmer seawater temperatures are expected to increase harmful algal blooms (HABs) occurrence, intensity, and distribution. Yet, the potential interactions between abiotic stressors and HABs are still poorly understood from ecological and seafood safety perspectives. The present study aimed to investigate, for the first time, the bioaccumulation/depuration mechanisms and ecotoxicological responses of juvenile gilthead seabream (Sparus aurata) exposed to paralytic shellfish toxins (PST) under different temperatures (18, 21, 24 °C). PST were detected in fish at the peak of the exposure period (day five, 0.22 µg g^-1 N-sulfocarbamoylGonyautoxin-1-2 (C1 and C2), 0.08 µg g^-1 Decarbamoylsaxitoxin (dcSTX) and 0.18 µg g^-1 Gonyautoxin-5 (B1)), being rapidly eliminated (within the first 24 h of depuration), regardless of exposure temperature. Increased temperatures led to significantly higher PST contamination (275 µg STX eq. kg^-1). During the trial, fish antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; glutathione S-transferase, GST) in both muscle and viscera were affected by temperature, whereas a significant induction of heat shock proteins (HSP70), Ubiquitin (Ub) activity (viscera), and lipid peroxidation (LPO; muscle) was observed under the combination of warming and PST exposure. The differential bioaccumulation and biomarker responses observed highlight the need to further understand the interactive effects between PST and abiotic stressors, to better estimate climate change impacts on HABs events, and to develop mitigation strategies to overcome the potential risks associated with seafood consumption.

A multidimensional concept for mercury neuronal and sensory toxicity in fish - From toxicokinetics and biochemistry to morphometry and behavior

BACKGROUND

Neuronal and sensory toxicity of mercury (Hg) compounds has been largely investigated in humans/mammals with a focus on public health, while research in fish is less prolific and dispersed by different species. Well-established premises for mammals have been governing fish research, but some contradictory findings suggest that knowledge translation between these animal groups needs prudence [e.g. the relative higher neurotoxicity of methylmercury (MeHg) vs. inorganic Hg (iHg)]. Biochemical/physiological differences between the groups (e.g. higher brain regeneration in fish) may determine distinct patterns. This review undertakes the challenge of identifying sensitive cellular targets, Hg-driven biochemical/physiological vulnerabilities in fish, while discriminating specificities for Hg forms.

SCOPE OF REVIEW

A functional neuroanatomical perspective was conceived, comprising: (i) Hg occurrence in the aquatic environment; (ii) toxicokinetics on central nervous system (CNS)/sensory organs; (iii) effects on neurotransmission; (iv) biochemical/physiological effects on CNS/sensory organs; (v) morpho-structural changes on CNS/sensory organs; (vi) behavioral effects. The literature was also analyzed to generate a multidimensional conceptualization translated into a Rubik's Cube where key factors/processes were proposed.

MAJOR CONCLUSIONS

Hg neurosensory toxicity was unequivocally demonstrated. Some correspondence with toxicity mechanisms described for mammals (mainly at biochemical level) was identified. Although the research has been dispersed by numerous fish species, 29 key factors/processes were pinpointed.

GENERAL SIGNIFICANCE

Future trends were identified and translated into 25 factors/processes to be addressed. Unveiling the neurosensory toxicity of Hg in fish has a major motivation of protecting ichtyopopulations and ecosystems, but can also provide fundamental knowledge to the field of human neurodevelopment.

Living in a multi-stressors environment: An integrated biomarker approach to assess the ecotoxicological response of meagre (Argyrosomus regius) to venlafaxine, warming and acidification

Pharmaceuticals, such as the antidepressant venlafaxine (VFX), have been frequently detected in coastal waters and marine biota, and there is a growing body of evidence that these pollutants can be toxic to non-target marine biota, even at low concentrations. Alongside, climate change effects (e.g. warming and acidification) can also affect marine species' physiological fitness and, consequently, compromising their ability to cope with the presence of pollutants. Yet, information regarding interactive effects between pollutants and climate change-related stressors is still scarce. Within this context, the present study aims to assess the differential ecotoxicological responses (antioxidant activity, heat shock response, protein degradation, endocrine disruption and neurotoxicity) of juvenile fish (Argyrosomus regius) tissues (muscle, gills, liver and brain) exposed to VFX (via water or feed), as well as to the interactive effects of warming (ΔT °C = +5 °C) and acidification (ΔpCO₂ ~ +1000 µatm, equivalent to ΔpH = -0.4 units), using an integrated multi-biomarker response (IBR) approach. Overall, results showed that VFX toxicity was strongly influenced by the uptake pathway, as well as by warming and acidification. More significant changes (e.g. increases surpassing 100% in lipid peroxidation, LPO, heat shock response protein content, HSP70/HSC70, and total ubiquitin content, Ub,) and higher IBR index values were observed when VFX exposure occurred via water (i.e. average IBR = 19, against 17 in VFX-feed treatment). The co-exposure to climate change-related stressors either enhanced (e.g. glutathione S-transferases activity (GST) in fish muscle was further increased by warming) or attenuated the changes elicited by VFX (e.g. vitellogenin, VTG, liver content increased with VFX feed exposure acting alone, but not when co-exposed with acidification). Yet, increased stress severity was observed when the three stressors acted simultaneously, particularly in fish exposed to VFX via water (i.e. average IBR = 21). Hence, the distinct fish tissues responses elicited by the different scenarios emphasized the relevance of performing multi-stressors ecotoxicological studies, as such approach enables a better estimation of the environmental hazards posed by pollutants in a changing ocean and, consequently, the development of strategies to mitigate them.

Bioaccumulation and ecotoxicological responses of juvenile white seabream (Diplodus sargus) exposed to triclosan, warming and acidification

Triclosan (TCS) is a synthetic microbial compound widely used in the formulation of various personal care products. Its frequent detection in marine ecosystems, along with its physical and chemical properties, suggest that TCS can be highly persistent, being easily bioaccumulated by biota and, therefore, eliciting various toxicological responses. Yet, TCS's mechanisms of bioaccumulation and toxicity still deserve further research, particularly focusing on the interactive effects with climate change-related stressors (e.g. warming and acidification), as both TCS chemical behaviour and marine species metabolism/physiology can be strongly influenced by the surrounding abiotic conditions. Hence, the aim of this study was to assess TCS bioaccumulation and ecotoxicological effects (i.e. animal fitness indexes, antioxidant activity, protein chaperoning and degradation, neurotoxicity and endocrine disruption) in three tissues (i.e. brain, liver and muscle) of juvenile Diplodus sargus exposed to the interactive effects of TCS dietary exposure (15.9 μg kg^-1 dw), seawater warming (ΔTºC = +5 °C) and acidification (ΔpCO₂ ∼ +1000 μatm, equivalent to ΔpH = -0.4 units). Muscle was the primary organ of TCS bioaccumulation, and climate change stressors, particularly warming, significantly reduced TCS bioaccumulation in all fish tissues. Furthermore, the negative ecotoxicological responses elicited by TCS were significantly altered by the co-exposure to acidification and/or warming, through either the enhancement (e.g. vitellogenin content) or counteraction/inhibition (e.g. heat shock proteins HSP70/HSC70 content) of molecular biomarker responses, with the combination of TCS plus acidification resulting in more severe alterations. Thus, the distinct patterns of TCS tissue bioaccumulation and ecotoxicological responses induced by the different scenarios emphasized the need to further understand the interactive effects between pollutants and abiotic conditions, as such knowledge enables a better estimation and mitigation of the toxicological impacts of climate change in marine ecosystems.

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

Early life stages of marine organisms are the most sensitive stages to environment stressors including pollutants. In order to understand the toxicological effects induced by MeHg exposure on juveniles of large yellow croaker (Pseudosciaena crocea), a toxicity test was performed wherein fish were exposed to sub-lethal concentrations of MeHg under laboratory conditions (18 ± 1°C; 26 ± 1 in salinity). After 30 days of 0–4.0 μg L^-1 MeHg exposure, SOD activity was significantly decreased in the 0.25, 1.0, and 4.0 μg L^-1 treatments; while CAT activity was significantly increased in the 4.0 μg L^-1 treatments; GSH level, GPx activity were significantly elevated in the 4.0 μg L^-1 treatments, respectively. Meanwhile, malondialdehyde content was also significantly increased in the 1.0 and 4.0 μg L^-1 treatments with respect to the control. Acetylcholinesterase activity was significantly decreased by 18.3, 25.2, and 21.7% in the 0.25, 1.0, and 4.0 μg L^-1 treatments, respectively. The expression of TCTP, GST3, Hsp70, Hsp27 mRNA were all up-regulated in juveniles with a dose-dependent manner exposed to MeHg. These results suggest that large yellow croaker juveniles have the potential to regulate the levels of antioxidant enzymes and initiate immune response in order to protect fish to some extent from oxidative stress induced by MeHg.

Antidepressants in a changing ocean: Venlafaxine uptake and elimination in juvenile fish (Argyrosomus regius) exposed to warming and acidification conditions

The presence of antidepressants, such as venlafaxine (VFX), in marine ecosystems is increasing, thus, potentially posing ecological and human health risks. The inherent mechanisms of VFX uptake and elimination still require further understanding, particularly accounting for the impact of climate change-related stressors, such as warming and acidification. Hence, the present work aimed to investigate, for the first time, the effects of increased seawater temperature (ΔT°C = +5 °C) and pCO₂ levels (ΔpCO₂ ∼1000 μatm, equivalent to ΔpH = -0.4 units) on the uptake and elimination of VFX in biological tissues (muscle, liver, brain) and plasma of juvenile meagre (Argyrosomus regius) exposed to VFX through two different exposure pathways (via water, i.e. [VFX ] ∼20 μg L^-1, and via feed, i.e. [VFX] ∼160 μg kg^-1 dry weight, dw). Overall, results showed that VFX can be uptaken by fish through both water and diet. Fish liver exhibited the highest VFX concentration (126.7 ± 86.5 μg kg^-1 and 6786.4 ± 1176.7 μg kg^-1 via feed and water exposures, respectively), as well as the highest tissue:plasma concentration ratio, followed in this order by brain and muscle, regardless of exposure route. Both warming and acidification decreased VFX uptake in liver, although VFX uptake in brain was favoured under warming conditions. Conversely, VFX elimination in liver was impaired by both stressors, particularly when acting simultaneously. The distinct patterns of VFX uptake and elimination observed in the different scenarios calls for a better understanding of the effects of exposure route and abiotic conditions on emerging contaminants' toxicokinetics.

Integrated multi-biomarker responses of juvenile seabass to diclofenac, warming and acidification co-exposure

Pharmaceutical drugs, such as diclofenac (DCF), are frequently detected in the marine environment, and recent evidence has pointed out their toxicity to non-target marine biota. Concomitantly, altered environmental conditions associated with climate change (e.g. warming and acidification) can also affect the physiology of marine organisms. Yet, the underlying interactions between these environmental stressors (pharmaceutical exposure and climate change-related stressors) still require a deeper understanding. Comprehending the influence of abiotic variables on chemical contaminants' toxicological attributes provides a broader view of the ecological consequences of climate change. Hence, the aim of this study was to assess the ecotoxicological responses of juvenile seabass Dicenthrachus labrax under the co-exposure to DCF (from dietary sources, 500 ± 36 ng kg^-1 dw), warming (ΔTºC = +5 °C) and acidification (ΔpCO₂ ∼1000 μatm, equivalent to ΔpH = -0.4 units), using an "Integrated Biomarker Response" (IBR) approach. Fish were exposed to these three stressors, acting alone or combined, for 28 days in a full cross-factorial design, and blood, brain, liver and muscle tissues were subsequently collected in order to evaluate: i) animal/organ fitness; ii) hematological parameters and iii) molecular biomarkers. Results not only confirmed the toxicological attributes of dietary exposure to DCF in marine fish species at the tissue (e.g. lower HSI), cellular (e.g. increased ENAs and lower erythrocytes viability) and molecular levels (e.g. increased oxidative stress, protein degradation, AChE activity and VTG synthesis), but also showed that such attributes are altered by warming and acidification. Hence, while acidification and/or warming enhanced some effects of DCF exposure (e.g. by further lowering erythrocyte viability, and increasing brain GST activity and Ub synthesis in muscle), the co-exposure to these abiotic stressors also resulted in a reversion/inhibition of some molecular responses (e.g. lower CAT and SOD inhibition and VTG synthesis). IBRs evidenced that an overall higher degree of stress (i.e. high IBR index) was associated with DCF and warming co-exposure, while the effects of acidification were less evident. The distinct responses observed when DCF acted alone or the animals were co-exposed to the drug together with warming and acidification not only highlighted the relevance of considering the interactions between multiple environmental stressors in ecotoxicological studies, but also suggested that the toxicity of pharmaceuticals can be aggravated by climate change-related stressors (particularly warming), thus, posing additional biological challenges to marine fish populations.

Fish energy budget under ocean warming and flame retardant exposure

Climate change and chemical contamination are global environmental threats of growing concern for the scientific community and regulatory authorities. Yet, the impacts and interactions of both stressors (particularly ocean warming and emerging chemical contaminants) on physiological responses of marine organisms remain unclear and still require further understanding. Within this context, the main goal of this study was to assess, for the first time, the effects of warming (+ 5 °C) and accumulation of a polybrominated diphenyl ether congener (BDE-209, brominated flame retardant) through dietary exposure on energy budget of the juvenile white seabream (Diplodus sargus). Specifically, growth (G), routine metabolism (R), excretion (faecal, F and nitrogenous losses, U) and food consumption (C) were calculated to obtain the energy budget. The results demonstrated that the energy proportion spent for G dominated the mode of the energy allocation of juvenile white seabream (56.0-67.8%), especially under the combined effect of warming plus BDE-209 exposure. Under all treatments, the energy channelled for R varied around 26% and a much smaller percentage was channelled for excretion (F: 4.3-16.0% and U: 2.3-3.3%). An opposite trend to G was observed to F, where the highest percentage (16.0 ± 0.9%) was found under control temperature and BDE-209 exposure via diet. In general, the parameters were significantly affected by increased temperature and flame retardant exposure, where higher levels occurred for: i) wet weight, relative growth rate, protein and ash contents under warming conditions, ii) only for O:N ratio under BDE-209 exposure via diet, and iii) for feed efficiency, ammonia excretion rate, routine metabolic rate and assimilation efficiency under the combination of both stressors. On the other hand, decreased viscerosomatic index was observed under warming and lower fat content was observed under the combined effect of both stressors. Overall, under future warming and chemical contamination conditions, fish energy budget was greatly affected, which may dictate negative cascading impacts at population and community levels. Further research combining other climate change stressors (e.g. acidification and hypoxia) and emerging chemical contaminants are needed to better understand and forecast such biological effects in a changing ocean.

Effects of heat and cadmium exposure on stress-related responses in the liver of female zebrafish: Heat increases cadmium toxicity

In this study, female zebrafish (Danio rerio) were exposed to 26°C or 34°C, 0 or 197μg/L cadmium (Cd), singly or in combination for 7days. Multiple stress-related indicators were evaluated in the liver. Mortality, lipid peroxidation (LPO) and ultrastructural damage increased significantly by Cd exposure alone, and were not affected by heat alone. Interestingly, the combined exposure increased LPO, ultrastructural damage, and mortality compared with Cd exposure alone. The results indicated that elevated temperature increased Cd toxicity, which could be explained by several reasons. Firstly, Cd-exposed fish failed to activate the antioxidant defense system under heat stress. Secondly, expression levels of heat shock protein 70 (HSP70) were not significantly up-regulated by heat in Cd-exposed fish but increased by 117 times in Cd-free fish. Besides, hypermethylation of heat shock factor (HSF) binding motif in HSP70 promoter was observed during the combined exposure, indicating that simultaneous exposure may have partially suppressed the cytoprotective up-regulation of HSP70. Thirdly, heat induced an immunosuppressive effect in Cd-exposed fish, as reflected by the reduced mRNA and activity levels of nitric oxide synthase (iNOS) and interleukin-1β (IL-1β) expression levels. Finally, heat down-regulated Zir-, Irt-like protein 8 (ZIP8) and copper transporter 1 (CTR1) and up-regulated metallothioneins (MTs) in Cd-exposed fish, possibly suggesting Cu and Zn depletion and Cd accumulation. Hence, our data provide evidences that warmer temperatures can potentiate Cd toxicity, involved in the regulation of gene transcription, enzymatic activity, and DNA methylation. We found that heat indicators showed varied sensitivity between normal and Cd-exposed fish, emphasizing that the field metal pollution should be carefully considered when evaluating effects of climate change.