Fish Toxicity Research Articles

Absorption and Distribution of Imidacloprid and Its Metabolites in Goldfish (Carassius auratus Linnaeus).

Imidacloprid (IMI) is the first-generation neonicotinoid insecticide. But, the long-term use of IMI as a pesticide has caused severe water pollution. Recently, the toxicity of IMI to aquatic organisms has received increasing attention. This study aimed to investigate the absorption and distribution of IMI in various tissues (gills, intestine, liver, muscle, brain and gonads) of goldfish through short-term and continuous exposure tests over 28 days. The results of short-term exposure indicated that the concentration of IMI and its metabolites in tissues at the transfer stage decreased steadily after 1 day of 40 mg/L IMI water treatment and was below the detection limit after 3 days. Continuous exposure for 28 days at various treatment concentrations showed that the concentrations of IMI and its metabolites differed significantly among the different tissues of the goldfish. In the 20 mg/L treatment group (S1), the highest concentration of IMI was found in the liver (12.04 μg/gtissue), followed by the intestine (9.91 μg/gtissue), muscle (6.20 μg/gtissue), gill (6.11 μg/gtissue), gonads (5.22 μg/gtissue) and brain (2.87 μg/gtissue). In the 40 mg/L treatment group (S2), the order of the tissue concentrations was similar to that of the S1 group, with the highest concentration observed in the liver (12.04 μg/gtissue), followed by the intestine (9.91 μg/gtissue), muscle (6.20 μg/gtissue), gill (6.11 μg/gtissue), gonads (5.22 μg/gtissue) and brain (2.87 μg/gtissue). Furthermore, the study detected 5-hydroxy-IMI, IMI urea and 6-chloronicotinic acid in IMI metabolites in all tissues, while IMI was detected only in the intestine and liver. Overall, the results of this study contribute to a better understanding of the metabolic behavior of IMI in organisms and provide new data to support the assessment of IMI toxicity in fish.

Toxicity assessment of poultry-waste biosynthesized nanosilver in Anabas testudineus (Bloch, 1792) for responsible and sustainable aquaculture development-A multi-biomarker approach

The current study investigates the potential utilization of poultry intestines for the synthesis of stable silver nanoparticles (AgNPs) and their impact on fish physiology. The AgNPs were synthesized and characterized using various analytical techniques. The toxicity of AgNPs on Anabas testudineus was evaluated, determining a 96-h LC50 value of 25.46 mg l−1. Subsequently, fish were exposed to concentrations corresponding to 1/10th, 1/25th, 1/50th, and 1/100th of the estimated LC50 for a duration of 60 days in a sub-acute study. A comprehensive range of biomarkers, including haematological, serum, oxidative stress, and metabolizing markers, were analyzed to assess the physiological responses of the fish. Additionally, histopathological examinations were conducted, and the accumulation of silver in biomarker organs was measured. The results indicate that silver tends to bioaccumulate in all biomarker organs in a dose- and time-dependent manner, except for the muscle tissue, where accumulation initially increased and subsequently decreased, demonstrating the fish's inherent ability for natural attenuation. Analysis of physiological data and integrated biomarker responses reveal that concentrations of 1/10th, 1/25th, and 1/50th of the LC50 can induce stress in the fish, while exposure to 1/100th of the LC50 shows minimal to no stress response. Overall, this study provides valuable insights into the toxicity and physiological responses of fish exposed to poultry waste biosynthesized AgNPs, offering potential applications in aquaculture while harnessing their unique features.

Possible ameliorative effect of dietary curcumin against water copper toxicity in Clarias gariepinus fish

Possible ameliorative effect of dietary curcumin against water copper toxicity in Clarias gariepinus fish

Salinity-dependent mitigation of naphthalene toxicity in migratory Takifugu obscurus juveniles: Implications for survival, oxidative stress, and osmoregulation

Naphthalene, an environmental pollutant classified as a polycyclic aromatic hydrocarbon (PAH), can induce toxicity in fish and other aquatic organisms. Through our investigation, we determined how Takifugu obscurus juveniles were affected by naphthalene (0, 2 mg L−1) exposure in terms of oxidative stress biomarkers and Na+/K+-ATPase activity in various tissues (gill, liver, kidney and muscle) under dissimilar salinities (0, 10 psu). Results suggest that naphthalene exposure significantly affects the survival of T. obscurus juveniles and leads to significant changes in the levels of malondialdehyde, superoxide dismutase, catalase, glutathione, and Na+/K+-ATPase activity, which are indicative of oxidative stress and emphasized the risks associated with osmoregulatory function. The higher salinity affected on the noxious effects of naphthalene can be observed, resulting in decreased biomarker levels and increased Na+/K+-ATPase activity. Salinity levels affected the uptake of naphthalene and its impact on different tissues, with high salinity conditions having mitigating effects on oxidative stress and naphthalene uptake in the liver and kidney tissues. Increased Na+/K+-ATPase activity was observed in all tissues treated with 10 psu and 2 mg L−1 naphthalene. Our findings deepen the understanding of T. obscurus juveniles' physiological responses to naphthalene exposure, and highlight the potential mitigating effects of salinity. These insights can inform the development of appropriate conservation and management practices to protect aquatic organisms from susceptibility.

Seasonal variation in non-point source heavy metal pollution in Satpara Lake and its toxicity in trout fish.

Heavy metal contamination in surface water is widespread throughout the world as a result of numerous anthropogenic activities and geo-genic mechanisms. This contamination is also affecting aquatic life, as fish have the potential to acquire heavy metals in their tissues making them vulnerable. Worldwide lakes are an important source of water for the inhabitants of the area. So, in the present study, we have focused on the Satpara Lake to check the extent of heavy metal pollution and their accumulation in fish to provide baseline data for metal pollution management. Samples were collected from three locations (inflow, center, and outflow sites) during two seasons (summer and winter). Inductively coupled plasma optical emission spectrometry (ICP-OES) was applied to analyze heavy metals concentration. Among the metals, Cd, Pb, As, and Fe revealed relatively higher concentrations. The highest concentration of heavy metal found in water and fish was of Cd, i.e., 8.87mg L-1 and 18.19mg L-1 in summer season, respectively. Arsenic concentration was also higher than the permissible limits in both water (0.76) and fish (1.17mg L-1). The water quality assessment showed that in the summer season, the HPI (heavy metal pollution index) value 253.01 was more than 100, indicating the bad quality of water for drinking purposes. However, the HPI value 35.72 was less than 100 in winter. Toxicity hazard calculation of fish in summer seasons gives Hi values greater than 10.0, indicating the acute effect on human health as compared to winter.

The Exploitation of Toxic Fish from the Terminal Pleistocene in Maritime Southeast Asia: A Case Study from the Mindoro Archaeological Sites, Philippines.

Representatives of the Diodontidae family (porcupinefish) are known to have been fished by prehistoric Indo-Pacific populations; however, the antiquity of the use of this family is thus far unknown. We report here on the presence of Diodontidae in the archaeological sites of Bubog I, II, and Bilat in Mindoro, Philippines, dating back to c. 13,000 BP (Before Present). This evidence demonstrates the early exploitation by islanders of poisonous fish. Every part of porcupinefish can be toxic, but the toxicity is mostly concentrated in some organs, while other parts are edible. The continuous presence of Diodontidae remains throughout the stratigraphic record of these Philippines shell middens suggests that porcupinefish were prepared by human inhabitants of the sites to render them safe for consumption, indicating an advanced cultural knowledge of the preparation needed to separate the toxic principle from the edible parts. This constitutes one of the rare examples of poison processing by humans, aside from the contentious wooden stick poison applicator from Border Cave (South Africa).

Potential toxicity of landfill leachate to zebrafish and mung beans.

Landfill leachate has become a major public health concern due to its adverse health effects. However, its toxicological effects have not been thoroughly determined because of its complex composition. To address this issue, two model organisms were used in this study, including mung beans and zebrafish. Bean seedlings were exposed to different concentrations of landfill leachate (1%, 5%, 10%, 15%, and 20%, v/v, leachate/deionized water) for 7days. Low concentrations (1%) of landfill leachate increased the growth of mung beans, whereas high concentrations (15% and 20%) of landfill leachate inhibited the growth and development of seedlings. Furthermore, landfill leachate reduced chlorophyll levels but increased malondialdehyde levels, leading to an increased rate of root-tip micronuclei. Zebrafish embryos were exposed to different concentrations of landfill leachate (0.5%, 1.0%, 1.2%, and 1.5%, v/v, leachate/E3 medium) for 120h. The results showed that landfill leachate significantly decreased lower levels of hatching rate and heart rate but increased the mortality and malformation rates of embryos. Moreover, 1.0% landfill leachate reduced the frequency of spontaneous movement and the light stimulation reaction of embryos. Embryos exposed to leachate showed less exploratory behavior and fewer mirror attacks in the black and white areas. Our results suggest that exposure to landfill leachate could cause developmental toxicity and genotoxicity in plants and fish. The findings can improve our understanding of the environmental toxicity of landfill leachate and provide additional evidence for its risk assessment and management.

Acute exposure to realistic concentrations of Bisphenol-A trigger health damage in fish: Blood parameters, gene expression, oxidative stress

Despite much information regarding BPA toxicity in fish and other aquatic organisms, data is still misleading as most studies have utilized concentrations several orders of magnitude higher than those typically found in the environment. As an illustration, eight of the ten studies investigating the impact of BPA on the biochemical and hematological parameters of fish have employed concentrations on the order of mg/L. Therefore, the results may not accurately represent the effects observed in the natural environment. Considering the information above, our study aimed to 1) determine whether or not realistic concentrations of BPA might alter the biochemical and blood parameters of Danio rerio and trigger an inflammatory response in the fish liver, brain, gills, and gut and 2) determine which organ could be more affected after exposure to this chemical. Findings pinpoint that realistic concentrations of BPA prompted a substantial increase in antioxidant and oxidant biomarkers in fish, triggering an oxidative stress response in all organs. Likewise, the expression of different genes related to inflammation and apoptosis response was significantly augmented in all organs. Our Pearson correlation shows gene expression was closely associated with the oxidative stress response. Regarding blood parameters, acute exposure to BPA generated biochemical and hematological parameters increased concentration-dependent. Thus, it can be concluded that BPA, at environmentally relevant concentrations, threatens aquatic species, as it prompts polychromasia and liver dysfunction in fish after acute exposure.

Growth, Reproduction, and Transgenerational Effects of Kinoprene on Moina macrocopa.

Juvenile hormone analogues (JHAs) are a kind of effective insecticide. These compounds have relatively low toxicity for fish, birds, and mammals, so they are increasingly used in insect pest control. However, JHAs may cause various adverse effects in crustaceans as in insects, because they have a close evolutionary relationship and possess similar juvenile hormone systems. To date, the chronic toxicities of JHAs over generations lacked intensive investigation. The present study evaluated the acute, chronic, and transgenerational effects of a terpenoid JHA, kinoprene, using the water flea Moina macrocopa. The result of acute exposure shows that kinoprene exhibited high toxicity to M. macrocopa. The chronic results indicate that kinoprene inhibited the survivorship, development, and reproduction of the organism. Moreover, the adverse effects induced by kinoprene continued in the F2 generation with no direct exposure but recovered in the F3 generation.

Effects of Alkylation on Potency of Benz[a]anthracene for AhR2 Transactivation in Nine Species of Freshwater Fish.

Polycyclic aromatic hydrocarbons (PAHs) are naturally occurring or anthropogenic organic chemicals that can activate the aryl hydrocarbon receptor 2 (AhR2) and induce toxicity in fishes. Alkyl PAHs are more abundant than nonalkylated PAHs in certain environmental matrices and there is growing evidence that alkylation can increase potency, dependent on the position of alkylation. However, it is unknown if the effect of alkylation on potency is conserved across species. In addition, relatively little is known regarding the extent of interspecies variation in sensitivity to PAHs and alkyl PAHs. Therefore, objectives of the present study were to characterize potency of benz[a]anthracene (BAA) and three alkylated homologues representing different alkylation positions in nine phylogenetically diverse species of fish using a standardized in vitro AhR2 transactivation assay. BAA and each alkylated homologue activated the AhR2 in a concentration-dependent manner in each species. Position-dependent effects on potency were observed in every species, but these effects were not consistent across species. Interspecies variation in sensitivity to AhR2 activation by each PAH was observed and ranged by up to 561-fold. Alkylation both increased and decreased the range of interspecies variation and sensitivity, but the potency of each alkylated homologue relative to BAA ranged by less than an order of magnitude among species. These results represent an early step toward the consideration of alkylated homologues for more objective ecological risk assessments of PAHs to native fishes. Environ Toxicol Chem 2023;42:1575-1585. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A meta-analysis on the toxicity of microcystin-LR to fish and mammals

Microcystin-leucine arginine (MC-LR), the most prevalent and dangerous microcystin, poses high risks to living organisms, especially fish and mammals. Although many studies have focused on the toxic effect on fish and mammals exposed to MC-LR, works that incorporate published data into a comprehensive comparison and analysis are still limited. Here, the adverse effects of oxidative stress markers, health, functional traits, and performance traits in fish and mammals were systematically verified by collecting data from 67 studies for the first time. Notably, we first found that the activities of malondialdehyde (MDA) (p < 0.05) and lactoperoxidase (LPO) always showed increases, whereas the growth (performance traits) always had a significant decrease (p < 0.001) under all variables of MC-LR exposure, i.e., exposure time, exposure concentration, exposure route, and even life stage. Additionally, our study first verified that the activities of MDA and LPO can be employed as oxidative stress indicators of MC-LR effects in fish and mammals instead of other biomarkers of oxidative stress, such as superoxide dismutase (SOD) and catalase (CAT), considered by previous studies. Growth may be regarded as a highly sensitive indicator of MC-LR toxicity in mammals and fish. At the same time, we first found that the impact of MC-LR exposure concentration on LPO, MDA, and growth is higher than that of exposure time, exposure route, and different life stages using the random forest (RF) model. In short, this work sheds light on the potential biochemical and individual toxicity of MC-LR exposure in fish and mammals.

Acute Toxicity Assessment and Prediction Models of Four Heavy Metals.

Water quality criteria (WQC) are developed to protect aquatic organisms. Toxicity data of local fish are essential to improve the applicability of WQC derivatives. However, the paucity of local cold-water fish toxicity data limits the development of WQC in China. Brachymystax lenok is a representative Chinese-endemic cold-water fish, which plays an important role in the characterization of metal toxicity in the water environment. Whereas, the ecotoxicological effects of copper, zinc, lead and cadmium, as well as its potential as a test species for the metal WQC, remain to be investigated. In our study, acute toxicity tests of copper, zinc, lead and cadmium were performed on this fish according to the OECD method and 96 h-LC50 values were calculated. The results showed that the 96 h-LC50 values of Cu2+, Zn2+, Pb2+ and Cd2+ for B. lenok were 134, 222, 514 and 734 μg/L, respectively. Toxicity data for freshwater species and Chinese-native species were collected and screened, and the mean acute values of each metal for each species were ranked. The results showed that the accumulation probability of zinc by B. lenok was the lowest and less than 15%. Thus, B. lenok was sensitive to Zn and can be considered as the test cold-water fish for derivation of Zn WQC. In addition, B. lenok in comparison with warm-water fish, we found that cold-water fish are not always more sensitive to heavy metals than warm-water fish. Finally, the models for toxic effects prediction of different heavy metals on the same species were constructed and evaluated the reliability of the model. We suggest that the alternative toxicity data provided by the simulations can be used to derive WQC for metals.

Therapeutic Role of Hemp (Cannabis sativa) Against Copper-Induced Toxicity in Labeo rohita and Cirrhinus mrigala.

For decades hemp has been used as a therapeutic agent for enhancing immunity in animals. Current study was conceptualized to find out the protective role of dietary hemp seed products (hemp seed oil (HO) and hemp seed (HS)) against copper-induced toxicity in fish. Fingerlings of Labeo rohita (Rohu) and Cirrhinus mrigala (Mrigal) were exposed to copper at 20% of the 96 h LC50 (1.34 and 1.52 ppm, respectively) for 30 days. Following Cu exposure, fish were maintained on two types of hemp (Cannabis sativa)-supplemented feeds, on graded levels of hemp seed oil (HO: 1%, 2%, 3%) and hemp seed (HS: 5%, 10%, 15%) for 50 days, while one group was the control (without any copper exposure as well as any supplementation). Copper exposure significantly increased (P < 0.05) WBCs, hematocrit, MCHV, eosinophils, and lymphocytes in L. rohita and also in C. mrigala as compared to control. Copper exposure also significantly (P < 0.05) changed lysozymes, plasma protein, and IgM in both species, in comparison to control. Moreover, alkaline phosphatase, bilirubin, serum glutamic-pyruvic transaminase, and aspartate transaminase were significantly (P < 0.05) changed by copper exposure in comparison to control in both species. Additionally, Antioxidant enzymes like catalase, superoxide dismutase, glutathione reductase, and glutathione peroxidase were also significantly (P < 0.05) increased in the brain, gills, liver, and muscle of copper-exposed group in both species as compared to control. Interestingly, all the altered parameter of blood, serum, liver function tests, and antioxidant enzymes (in different organs) because of copper toxicity were successfully reverted to normal level in hemp seed oil (HO) and hemp seed (HS)-supplemented fed groups of both species. In conclusion, hemp seed supplementation showed significant (P < 0.05) improved results against copper toxicity. Thus, it could be recommended as an animal feed ingredient for its therapeutic role.

Investigation of Selected Heavy Metals, Histopathological and Oxidative Stress Responses of Nile Tilapia, Oreochromis niloticus in Water from the Hadejia-Nguru Wetlands Nigeria

Hadejia-Nguru wetland has been known to be a productive area of Agricultural engagements and fisheries activities allowing for intensive farming and fishing activities, effluents from agricultural activities, sewage, and chemical seepages enter this water body. This study investigated the levels of several heavy metals Mercury (Hg), Lead (Pb), Cadmium (Cd),Chromium (Cr), and Aluminum (Al) in O. niloticus tissues (gills, liver, muscle) collected from five sampling sites in the study area. Tissue histology and the presence of antioxidant enzymes revealed the degree of tissue damage and stress in fish. The results for heavy metals showed concentrations in the order Hg&gt;Cr&gt;Pb&gt;Al&gt;Cd, which are higher than the maximum residue limits recommended by FAO and WHO. Superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and reduced glutathione (GSH) activities were observed at high concentrations in gills, liver, and muscle. Liver of the fish showed a high level of SOD concentration of 18.3μg/ml, followed by a concentration of 16.93 μg/ml in the gills, and CAT with a concentration of 1.48 U/ml was observed in the liver, MDA was highest in the liver with a concentration level of 1.08n/mol and there was no significant difference between MDA concentrations in liver and other organs (P &lt; 0.05). Reduced glutathione levels of 18.36 μg/ml was seen in the liver of the fish. Histopathology of the select organs i.e. gills, liver and muscle cells showed that the organs of the fish were affected by the level of toxicity in the Hadejia-Nguru environment. The presence of metal toxicity, antioxidant enzymes, and tissue damage in fish is an indication of contamination and serves as a means for monitoring the safety of freshwater organisms.

Local and Traditional Ecological Knowledge of Fish Poisoning in Fiji.

Fish poisoning (FP) affects human health, trade and livelihood in Fiji, where management has depended mainly on traditional ecological knowledge (TEK). This paper investigated and documented this TEK through a 2-day stakeholder workshop, group consultation, in-depth interviews, field observations, and analyses of survey data from the Ministry of Fisheries, Fiji. Six TEK topics were identified and classified as preventative and treatment options. The preventive approach involves identifying toxic reef fishes, the spawning season of edible seaworms, hotspot areas of toxic fishes, folk tests, and locating and removing toxic organs. For example, 34 reef fish species were identified as toxic. The FP season was associated with the spawning of balolo (edible seaworm) and the warmer months of October to April (cyclone seasons). Two well-known toxic hotspots associated with an abundance of bulewa (soft coral) were identified. Folk tests and locating and removing toxic fish organs are also practised for moray eels and pufferfish. At the same time, various locally available herbal plants are used to treat FP as the second line of defence. The TEK collated in this work can help local authorities better identify the sources of toxicity, and applying TEK preventive measures could stem the tide of fish poisoning in Fiji.

Nutritional profile and heavy metal contamination of nursery, grower, and finisher feeds of tilapia (Oreochromis niloticus) in Bangladesh

Tilapia, the third most cultured fish, is a part of the daily diet of more than 50% of the population of Bangladesh. Thus, adequate nutrition and toxic metal-free tilapia fish feeds are the prerequisites of sustainable aquaculture. The present study was carried out to investigate the nutritional profile and heavy metal pollution in nursery, grower, and finisher types of feeds of tilapia commercially available in Bangladesh. The proximate composition (moisture, protein, lipid, ash, crude fibre, and carbohydrate), mineral nutrients, fatty acid profile, and heavy metals (Pb, Cd, Cr, Ni, Cu, and Zn) of feed samples were assessed. Low protein content and the absence of essential fatty acids mark the feeds as low-quality diets. A significant amount of trace metals were also detected in the feeds, posing a direct threat to the health of the fish and, ultimately, to consumers. The results revealed the highest Zn concentration in all tilapia feed samples. The descending order of heavy metal concentrations was identified as Zn>Ni>Pb>Cu>Cr in nursery feeds, Zn>Cu>Cr in grower feeds, and Zn>Ni>Cu>Cr>Cd in finisher feeds. Pb and Cr values were higher than the recommended values set by FAO. Therefore, strong monitoring is recommended to ensure the optimum quality and safety feeds.

The metabolites could not be ignored: A comparative study of the metabolite norfluoxetine with its parent fluoxetine on zebrafish (Danio rerio)

The ubiquitous pharmaceuticals in aquatic environments have attracted huge attention due to their significant risks to humans and ecosystems. However, even though the knowledge of the negative effects induced by the parent pharmaceuticals is quite extensive, little is known about their metabolites for a long time. This study provides systematical knowledge about the potential toxicity of metabolite norfluoxetine and its parent fluoxetine on zebrafish (Danio rerio) at the early life stage. The results showed that the metabolite norfluoxetine had similar acute toxicity in fish with the parent fluoxetine. For the altered fish development, there was no significant difference in most cases between the two pharmaceuticals. Compared to the control, the metabolite markedly inhibited the locomotor behavior under light-to-dark transitions, which was comparable to the parent. Norfluoxetine could easily accumulate but hardly eliminate from fish, relative to fluoxetine. In addition, the accumulated fluoxetine in zebrafish may rapidly metabolize to norfluoxetine and then be eliminated through different metabolic pathways. The functional genes related to serotonergic process (5-ht1aa, 5-ht2c, slc6a4b, and vmat), early growth (egr4), and circadian rhythm (per2) were downregulated by both the norfluoxetine and fluoxetine, indicative of the same mode-of-action of norfluoxetine with its parent in these functions. Meanwhile, the alterations caused by norfluoxetine were more pronounced than that of fluoxetine in the genes of 5-ht2c, slc6a4b, vmat, and per2. The molecular docking also confirmed that norfluoxetine could bind with serotonin transporter protein in the same as fluoxetine with a lower binding free energy. Overall, the metabolite norfluoxetine could induce similar and even more toxic effects on zebrafish with the same mode of action. The different and binding energy of the metabolite norfluoxetine and its parent fluoxetine on zebrafish may be responsible for the differentiated effects. It highlights the risks of the metabolite norfluoxetine in the aquatic environment could not be ignored.

Reproductive toxicity in marine medaka (Oryzias melastigma) due to embryonic exposure to PCB 28 or 4’-OH-PCB 65

Previous studies have shown that juvenile or adult exposure to polychlorinated biphenyls (PCBs) induces alterations in reproductive functions (e.g., reduced fertilization rate) and behavior (e.g., reduced nest maintenance) in fish. Embryonic exposures to other endocrine disrupting chemicals have been reported to induce long-term reproductive toxicity in fish. However, the effects of embryonic exposure to PCBs or their metabolites, OH-PCBs, on long-term reproductive function in fish are unknown. In the present study, we used the marine medaka fish (Oryzias melastigma) as a model to assess the reproductive endpoints in response to embryonic exposure to either PCB 28 or 4’-OH-PCB 65. Our results showed that the sex ratio of marine medaka was feminized by exposure to 4’-OH-PCB 65. Fecundity was decreased in the medaka treated with either PCB 28 or 4’-OH-PCB 65, whereas the medaka from embryonic exposure to 4’-OH-PCB 65 additionally exhibited reduced fertilization and a reduction in the hatching success rate of offspring, as well as decreased sperm motility. Serum 11-KT concentrations were reduced in the PCB 28-treated medaka, and serum estradiol (E2)/testosterone (T) and E2/11-ketotestosterone (11-KT) ratios were decreased in the 4’-OH-PCB 65-treated medaka. To explain these observations at the molecular level, transcriptomic analysis of the gonads was performed. Bioinformatic analysis using Gene Ontology and Ingenuity Pathway Analysis revealed that genes involved in various pathways potentially involved in reproductive functions (e.g., steroid metabolism and cholesterol homeostasis) were differentially expressed in the testes and ovaries of either PCB- or OH-PCB-treated medaka. Thus, the long-term reproductive toxicity in fish due to embryonic exposure to PCB or OH-PCB should be considered for environmental risk assessment.

Responses of oxidative stress biomarkers of freshwater fish (Oreochromis niloticus) exposed to Cr6+, Hg2+, Ni2+ and Zn2+ in differing calcium levels

Freshwaters from different geographical locations show different hardness, affecting metal uptake and toxicity in fish. The most important ion that determines water hardness is calcium. In this study, acute and chronic effects of metals on the oxidative stress biomarkers in the liver of freshwater fish (Oreochromis niloticus) were investigated in differing Ca2+ (30, 60 and 120 mg Ca2+/L) levels. Fish were exposed to Cr6+, Ni2+ and Zn2+ (30 μM) and Hg2+ (0.3 μM) for 3 days in acute experiments, while they were exposed to Cr6+, Ni2+ and Zn+2 (10 μM) and Hg2+ 0.03 μM) for 30 days in chronic experiments. Data showed that the oxidative stress biomarkers significantly (p < 0.05) altered after metal exposures at all calcium levels, though there was no significant change (p > 0.05) among calcium controls. In both acute and chronic exposures, catalase CAT) and superoxide dismutase (SOD) activities increased significantly, while glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione S-transferase (GST) activities decreased. There were significant decreases in total glutathione (GSH) levels in acute exposures, though GSH levels increased in chronic exposures. Malondialdehyde (MDA) levels significantly increased in both durations. The highest significant alterations in the biomarkers occurred at the lowest Ca2+ levels. GPX and GST were found to be the most sensitive enzymes in all exposures and the least alterations in biomarker response occurred in fish exposed to Ni2+. This study demonstrated that calcium levels (hardness) were important factors in the evaluation of metal toxicity for freshwater fish.

Differential Cell Metabolic Pathways in Gills and Liver of Fish (White Seabream Diplodus sargus) Coping with Dietary Methylmercury Exposure

Mercury (Hg) is a dangerous and persistent trace element. Its organic and highly toxic form, methylmercury (MeHg), easily crosses biological membranes and accumulates in biota. Nevertheless, understanding the mechanisms of dietary MeHg toxicity in fish remains a challenge. A time-course experiment was conducted with juvenile white seabreams, Diplodus sargus (Linnaeus, 1758), exposed to realistic levels of MeHg in feed (8.7 μg g-1, dry weight), comprising exposure (E; 7 and 14 days) and post-exposure (PE; 28 days) periods. Total Hg levels increased with time in gills and liver during E and decreased significantly in PE (though levels of control fish were reached only for gills), with liver exhibiting higher levels (2.7 times) than gills. Nuclear magnetic resonance (NMR)-based metabolomics revealed multiple and often differential metabolic changes between fish organs. Gills exhibited protein catabolism, disturbances in cholinergic neurotransmission, and changes in osmoregulation and lipid and energy metabolism. However, dietary MeHg exposure provoked altered protein metabolism in the liver with decreased amino acids, likely for activation of defensive strategies. PE allowed for the partial recovery of both organs, even if with occurrence of oxidative stress and changes of energy metabolism. Overall, these findings support organ-specific responses according to their sensitivity to Hg exposure, pointing out that indications obtained in biomonitoring studies may depend also on the selected organ.