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This review summarizes the current knowledge on the contribution of metals to the development of oxidative stress in fish. Metals are important inducers of oxidative stress in aquatic organisms, promoting formation of reactive oxygen species through two mechanisms. Redox active metals generate reactive oxygen species through redox cycling, while metals without redox potential impair antioxidant defences, especially that of thiol-containing antioxidants and enzymes. Elevated levels of reactive oxygen species lead to oxidative damage including lipid peroxidation, protein and DNA oxidation, and enzyme inactivation. Antioxidant defences include the enzyme system and low molecular weight antioxidants. Metal-binding proteins, such as ferritin, ceruloplasmin and metallothioneins, have special functions in the detoxification of toxic metals and also play a role in the metabolism and homeostasis of essential metals. Recent studies of metallothioneins as biomarkers indicate that quantitative analysis of mRNA expression of metallothionein genes can be appropriate in cases with elevated levels of metals and no evidence of oxidative damage in fish tissue. Components of the antioxidant defence are used as biochemical markers of oxidative stress. These markers may be manifested differently in the field than in results found in laboratory studies. A complex approach should be taken in field studies of metal contamination of the aquatic environment.

The present study aimed to evaluate the biochemical and antioxidant responses of common carp after exposure to the antiepileptic and analgesic drug gabapentin at concentrations of 0.1, 1, 10, and 100 μg/l for 4 weeks. The exposure to the highest two concentrations resulted in significant changes in plasma indices such as glucose (only group 100 μg/l), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), lipase, creatine kinase (CK), amylase as well as butyrylcholinesterase (BChE). Similar trends were found in both groups exposed to the environmentally relevant concentrations (i.e., 0.1 and 1 μg/l). In addition, a significant increase in the ferric-reducing power of the plasma was noted in all treated groups. Numerous changes in antioxidant enzymes, superoxide dismutase, catalase, glutathione-S-transferase, as well as lipid peroxidation, were observed especially in the caudal kidney in the group exposed to 100 μg/l. Significant findings were also confirmed in the group exposed to an environmentally relevant concentration (1 μg/l), with a decrease in superoxide dismutase in the gill and an increased lipoperoxidation in the caudal kidney. Our research shows that subchronic exposure to gabapentin may pose a significant risk to non-target aquatic organisms, such as disruption of metabolic pathways or induction of oxidative stress, even at environmentally relevant concentrations.

The use of  (fish cell lines) is a cost-effective, very rapid, and informative tool for toxicological assessments. Using the neutral red (NR) assay, we compared the acute toxicity (20hEC50) of twenty-six chemical substances on a rainbow trout gonad cell line (RTG-2) with their acute toxicity to Barbados Millions (48hLC50, OECD 203) and crustacean (48hEC50, OECD 202). The 20hEC50 values obtained by the NR assay were higher in nearly all the cases when compared to the 48hLC50 in  and the 48hEC50 in  indicating that the sensitivity of the RTG-2 cell line was lower compared to  and . A high (  = 0.89) and significant ( 0.001) correlation was recorded between the 20hEC50 values of the RTG-2 and the 48hEC50 values of  . The correlation between the 20hEC50 values of the RTG-2 and the 48hLC50 values of  was lower (  = 0.65; 0.001), but also significant. The authors recommend use of the NR assay on the RTG-2 cell lines as a screening protocol to evaluate the toxicity of xenobiotics in aquatic environments to narrow the spectrum of the concentrations for the fish toxicity test.

The occurrence of human as well as veterinary drug residues in surface water is caused by their insufficient removal ability from wastewater. Drug residues disturb the natural balance of water ecosystem, have a negative effect on non-target organisms and pose a significant risk for human health. The main aim of this study was to determine the concentration of residues of eight drugs from the group of sulfonamides (sulfathiazole, sulfadiazine, sulfamethazine, sulfamethoxazole, sulfadimethoxine, sulfadoxine, sulfamerazine, sulfachlorpyridazine), four drugs from the non-steroidal anti-inflammatory drug group (ibuprofen, ketoprofen, naproxen, diclofenac) and one representative of the analgesics-antipyretics group [paracetamol (acetaminophen)] in the surface water of the Elbe river basin. A total of 65 samples of surface water from the Elbe river basin were taken during August 2018 when the weather was constant without any significant fluctuations. The analysis was performed by means of liquid chromatography with tandem mass spectrometry (LC-MS/MS). The results have shown the numerous occurrences of sulfamethoxazole, ibuprofen, naproxen, diclofenac and paracetamol (acetaminophen). A statistically significant negative correlation between the river flow rate in the monitored locations and the residue concentration was found for ibuprofen, naproxen, diclofenac and paracetamol (acetaminophen). The most significant findings of the monitored drug residues were mostly determined in samples from small streams below larger urban settlements with a hospital or other health facilities.

Contamination of Pansky Pond, in March 2013, with 119 mg/l aluminium, and 87 mg/l iron by acidic (pH 3.17) inflow from a nearby quarry caused fish die-off, while exhibiting symptoms of suffocation. Transformation of soluble forms of aluminium and iron into insoluble forms occurred on fish gill where the content of aluminium and iron was 100-fold and 12-fold, respectively, that found in control fish in an unaffected pond. In addition to insoluble aluminium and iron, gills showed presence of iron bacteria. Histopathology was characterised by expression of reactive processes and regressive alterations resulting in gill tissue necrosis. Impairment of the excretory function of gills was reflected in significantly (P < 0.01) higher concentrations of ammonia in the blood plasma of exposed fish compared to the control. Damage to parenchymatous tissues (kidney, liver, spleen) of the exposed fish was manifested as dystrophic alterations, higher aluminium and iron content, and enhanced activity of transaminases in blood plasma compared to the control.

This study describes a case of poisoning by pyrrolizidine alkaloids in a horse. To the best of the author's knowledge, this is the first confirmed case of  poisoning. A six-year-old 450-kg Irish cob mare was presented to the Equine Clinic of the University of Veterinary Sciences Brno (Czechia) with symptoms of hepatic encephalopathy, which progressively worsened with time despite intensive therapy and led to euthanasia. A complex diagnostic and therapeutic approach including the post-mortem patoanatomical and histopathological examination is described here. Regarding the histopathology of the liver, there was necrosis with haemorrhage, fatty changes and inflammation. A later inspection of the grazing area revealed the presence of  (wood ragwort). A sensitive chromatographic method was used to determine the pyrrolizidine alkaloids and their metabolites in the plasma and the liver. In both of the samples, metabolites of pyrrolizidine alkaloids were detected. Although pyrrolizidine alkaloid poisoning was proven, the histopathological findings typical for this disease were absent. It is clear from our case that the histopathology in cases of poisoning by pyrrolizidine alkaloids may not always be conclusive.

In the present study, the effects of sub-lethal sub-chronic doses of ibuprofen, diclofenac, and carbamazepine alone, and in combination (concentration range 0.02–60 µg/l), on the early life stages of tench (Tinca tinca) were investigated. The lower concentrations of pharmaceuticals tested (0.02, 0.2, 2 µg/l) represent the concentration values of these substances commonly present in surface waters or effluents from wastewater treatment plants. Multiple biomarkers of biotransformation, antioxidant defence systems, and lipid peroxidation were determined in fish after 35 days of exposure. The evaluated pharmaceuticals induced oxidative stress in fish both alone and in combination with each other. Generally, 60 µg/l of each single pharmaceutical influenced the activity of antioxidant enzymes significantly (P < 0.05), whereas the same concentration of these pharmaceuticals in combination (1 : 1 : 1) did not have any impact on the activity of these enzymes. However, changes in biotransformation and antioxidant enzymes were apparent if lower concentrations of these pharmaceuticals were administered in the mixture. Significant changes (P < 0.05) in the activities of glutathione reductase, glutathione peroxidase, and glutathione-S-transferase were observed even at environmental concentration ranges. A significant effect (P < 0.05) on lipid peroxidation levels was found only in the experimental group exposed to carbamazepine.

Malachite green has been used as an effective compound to control external fungal and protozoan infections of fish since 1933 but it has never been registered as a veterinary drug for use in food fish because of its potential carcinogenicity, mutagenicity and teratogenicity in mammals. The present paper reviews negative side-effects of malachite green including its accumulation and persistence in fish that have been treated and describes other alternative substances for the treatment of fish and fish eggs.

Cadmium is one of the most important environmental contaminants. Animals grazing on natural pastures are particularly exposed to cadmium. Sheep are mostly reared in extensive and grazing systems. Therefore, sheep may accumulate larger amounts of cadmium compared to other ruminant species and are a good indicator of exposure to cadmium contamination in a given area. The determination of cadmium concentrations in the muscles, livers and kidneys of lambs and sheep was carried out in the Czech Republic during the period 2001-2022. The average cadmium content in the livers and kidneys of all the lambs was 0.037 ± 0.006 and 0.061 ± 0.013 mg.kg , respectively. The average cadmium content in the livers and kidneys of all the sheep was 0.319 ± 0.047 and 1.255 ± 0.204 mg.kg , respectively. The maximum limit for human consumption was not exceeded in any of the 24 samples in the lambs but was exceeded in 5 of 33 liver samples and 12 of 33 kidney samples in the adult sheep. The average value of cadmium in the muscles of the lambs and sheep was 0.004 ± 0.001 mg.kg . The maximum limit for human consumption was not exceeded in any muscle sample. The cadmium content in both the liver and in the kidney differs significantly between the lambs and sheep, being higher in the sheep (  < 0.001 for both comparisons). No statistically significant trend of a decrease in the cadmium content in the lamb and sheep tissues was found during the observed time (  > 0.05). We can sum up that there is an evident need for further monitoring of the cadmium concentration in lamb and sheep tissues in the Czech Republic.

In the European Union, the use of the insecticide NeemAzal T/S (standardised variant 1% of the active ingredient azadirachtin) is authorised in organic agriculture. The objective of this study was to determine the toxic effects of NeemAzal T/S at concentrations of 3, 10, 30, and 60 mg/lon the morphometric and condition characteristics, mortality, hatching, and histopathology of early-life stages of common carp (Cyprinus carpio L.) as a non-target aquatic organism, as well as related effects of NeemAzal T/S on selected indices of oxidative stress in the same organism. The embryo-larval toxicity test was performed according to OECD Guidelines 210 (Fish, Early-life Stage Toxicity Test). NeemAzal T/S exposure induced slow hatching on the first day and increased cumulative mortality in groups exposed to the insecticide. No effect on morphometric or condition characteristics was observed after 31 days of exposure. Histopathological changes of the gills were found at the highest concentration of 60 mg/lof NeemAzal T/S. Exposure at 30 mg/lwas associated with significantly (P < 0.01) increased glutathione peroxidase and glutathione S-transferase (P < 0.05) activities compared to the control group. The content of oxidised lipids was significantly higher (P < 0.05) in the 3, 10, and 30 mg/l experimental groups than in the controls. NeemAzal T/S exerted a significant negative influence on histopathological parameters in the embryo and larvae of common carp, as well as on the indices of oxidative stress in the same organism.