Exposure to environmentally relevant concentrations of deltamethrin renders the Chinese rare minnow (Gobiocypris rarus) vulnerable to Pseudomonas fluorescens infection

miR-29b-triggered epigenetic regulation of cardiotoxicity following exposure to deltamethrin in zebrafish

Deltamethrin is a classical pyrethroid insecticide that is frequently detected in aquatic environments and organisms. Furthermore, deltamethrin has been detected in samples related to human health and is a potential risk to public health. This study aimed to investigate the mechanism of cardiotoxicity induced by deltamethrin. Zebrafish were exposed to 0.005, 0.05, or 0.5 μg/L deltamethrin for 28 days. The results showed a significant reduction in male reproduction compared to female reproduction. Additionally, the heart rate decreased by 15.75 % in F1 after parental exposure to 0.5 μg/L deltamethrin. To evaluate cardiotoxicity, deltamethrin was administered to the zebrafish embryos. By using miRNA-Seq and bioinformatics analysis, it was discovered that miR-29b functions as a toxic regulator by targeting dnmts. The overexpression of miR-29b and inhibition of dnmts resulted in cardiac abnormalities, such as pericardial edema, bradycardia, and abnormal expression of genes related to the heart. Similar changes in the levels of miR-29b and dnmts were also detected in the gonads of F0 males and F1 embryos, confirming their effects. Overall, the results suggest that deltamethrin may have adverse effects on heart development in early-stage zebrafish and on reproduction in adult zebrafish. Furthermore, epigenetic modifications may threaten the cardiac function of offspring.

Immune response of Rhinogobio ventralis to Ichthyophthirius multifiliis infection: Insights from histopathological and real-time gene expression analyses

Ichthyophthirius multifiliis is a parasite that poses a considerable threat to aquaculture and the ornamental fish industry, but with limited effective treatment options available. This study employed RT-qPCR to detect and analyze the expression changes of partial toll-like receptor (TLR) genes (TLR1 and TLR21), adapter protein and signal transduction molecule genes (MyD88, TRIF, NF-κB, IRAK4, and IRF3), and cytokines (IL-6, IL-8, IL-13, CXC-α and CXCR1), as well as complement C3, in the skin, gill, fin, liver, head kidney and spleen of Rhinogobio ventralis under different infection conditions. Additionally, tissue sections and scanning electron microscopy were utilized to observe the pathological changes in the gills and fins of R. ventralis after infection with I. multifiliis. The expression patterns of TLR-related DEGs (differentially expressed genes) in diseased wild fish were analyzed, revealing upregulation of TLR1, TLR21, MyD88, NF-κB, IRAK4, TRIF, IRF3, IL-6, IL-8, IL-13, CXC-α, CXCR1, and C3 genes in various tissues, indicating that these genes may be involved in the immune response of R. ventralis to I. multifiliis infection. To further analyze the gene expression of sampled from the field, an artificial infection model of R. ventralis was established under laboratory conditions, with additional sampling from the skin and fins. These genes continued to show varying degrees of upregulation, but the results were not entirely consistent with those from Wudongde samples, which may be due to the more complex environment in the wild or differences in the degree of I. multifiliis infection in wild fish. The infection of I. multifiliis caused severe damage to the gills and fins of R. ventralis, characterized by extensive secretions on the gill and fin surfaces, with the presence of attached I. multifiliis trophonts, including damage and loss of gill filaments, swollen gill lamellae, and deformed gill plates, as well as cell proliferation and necrosis of gill epithelial cells. This study sheds light on the role of the TLR signaling pathway in resisting I. multifiliis infection and its associated histopathological changes in R. ventralis, providing valuable insights for the prevention and treatment of I. multifiliis infection in R. ventralis.

Environmentally relevant concentrations of naphthenic acids initiate intestinal injury and gut microbiota dysbiosis in marine medaka (Oryzias melastigma)

Naphthenic acids (NAs) are important pollutants in marine crude oils and have obvious toxic effects on marine organisms. However, the effects of NAs on the intestine are largely unknown. Thus, we evaluated the effects of NAs exposure in the intestines of marine medaka. Fish were experimentally exposed to NAs (0.5 mg/L, 5 mg/L, and 10 mg/L) for 96 h and monitored for changes in intestinal histology, markers of oxidative stress, and intestinal microbiome responses. Significant mucosal damage, inflammation, and oxidative stress were observed in the intestines of marine medaka after exposure to NAs. In addition, significant changes in the gut microbiota were observed. Specifically, the relative abundance of Proteobacteria decreased, while that of Verrucomicrobiota increased in the high-concentration exposure group. In addition, nutrient synthesis and metabolism in the gut were affected. The results of this study contribute to a better understanding of the ecological risk of different concentrations of NAs to marine organisms. CAPSULE ABSTRACT: Changes in the gut microbial community of marine medaka (Oryzias melastigma) caused by naphthenic acids in the marine environment were investigated through the assessment of gut inflammatory factors and comprehensive analysis using 16S rDNA high-throughput sequencing. The results indicated the induction of intestinal inflammation and changes in the structural composition of the intestinal flora.

Contribution of Immune Responses to the Cardiotoxicity and Hepatotoxicity of Deltamethrin in Early Life Stage Zebrafish (Danio rerio)

Deltamethrin (DM) is a widely used insecticide that has demonstrated developmental toxicity in the early life stages of fish. To better characterize the underlying mechanisms, embryos from Tg(cmlc2:RFP), Tg(apo14:GFP), and Tg(mpx:GFP) transgenic strains of zebrafish were exposed to nominal DM concentrations of 0.1, 1, 10, 25, and 50 μg/L until 120 h post-fertilization (hpf). Heart size increased 56.7%, and liver size was reduced by 17.1% in zebrafish exposed to 22.7 and 24.2 μg/L DM, respectively. RNA sequencing and bioinformatic analyses predicted that key biological processes affected by DM exposure were related to inflammatory responses. Expression of IL-1 protein was increased by 69.0% in the 24.4 μg/L DM treatment, and aggregation of neutrophils in cardiac and hepatic histologic sections was also observed. Coexposure to resatorvid, an anti-inflammatory agent, mitigated inflammatory responses and cardiac toxicity induced by DM and also restored liver biomass. Our data indicated a complex proinflammatory mechanism underlying DM-induced cardiotoxicity and hepatotoxicity which may be important for key events of adverse outcomes and associated risks of DM to early life stages of fish.

Niclosamide subacute exposure alters the immune response and microbiota of the gill and gut in black carp larvae, Mylopharyngodon piceus

Niclosamide (NIC) is a commonly used insecticide and molluscicide in the prevention and treatment of parasitic diseases in fish. The utilization of NIC has the potential to disrupt the microbial community present on the mucosal tissue of fish, leading to localized inflammatory responses. The objective of this study was to evaluate the impact of NIC on the immune system and bacterial populations within the gill and gut of Mylopharyngodon piceus. Fish were subjected to varying concentrations of NIC, including a control group (0 μg/L), a low NIC group (15% 96 h LC50, LNG, 9.8 μg/L), and a high NIC group (80% 96 h LC50, HNG, 52.5 μg/L). Gill and gut samples were collected 28 days post-exposure for analysis. The findings revealed that the 96-h LC50 for NIC was determined to be 65.7 μg/L, and histopathological examination demonstrated that exposure to NIC resulted in gill filament subepithelial edema, exfoliation, degeneration, and a decrease in gill filament length. Furthermore, the gut exhibited apical enterocyte degeneration and leucocyte infiltration following NIC exposure. Additionally, NIC exposure led to a significant elevation in the levels of immunoglobulin M (IgM), complement component 3 (C3), and complement component 4 (C4) in both gill and gut tissues. Moreover, the activity of lysozyme (LYZ) was enhanced in the gill, while the activities of peroxidase (POD) and immunoglobulin T (IgT) were increased in gut tissue. The exposure to NIC resulted in enhanced mRNA expression of c3, c9, tnfα, il6, il8, and il11 in the gill tissue, while decreasing c3 and il8 expression in the gut tissue. Furthermore, the natural resistance-associated macrophage protein (nramp) mRNA increased, and liver-expressed antimicrobial peptide 2 (leap2) mRNA decreased in gill and gut tissues. And hepcidin (hepc) mRNA levels rose in gill but fell in gut tissue. NIC exposure also led to a decrease in gill bacterial richness and diversity, which significantly differed from the control group, although this separation was not significant in the gut tissue. In conclusion, the administration of NIC resulted in alterations in both the immune response and mucosal microbiota of fish. Furthermore, it was noted that gills displayed a heightened vulnerability to sublethal effects of NIC in comparison to gut tissues.

Implications of deltamethrin on hematology, cardiac pathology, and gene expression in Nile tilapia (Oreochromis niloticus) and its possible amelioration with Shatavari (Asparagus racemosus)

Deltamethrin (DM) is one of the extensively used pyrethroids for controlling ectoparasites. Unfortunately, DM is highly toxic to fish as it primarily targets the sodium channels of the plasma membrane thereby affecting their cardiac and nervous systems. The present study investigated the protective efficacy of Shatavari (Asparagus racemosus) against DM-induced cardiotoxicity in Nile tilapia (Oreochromis niloticus). The fish were segregated into nine groups having 36 fish/group maintained in triplicates exposed to DM (1 µg/L) and fed with a diet containing three different concentrations (10 g, 20 g, and 30 g/kg feed) of aqueous extract of A. racemosus (ARE) for 21 days. DM caused significant alterations in the blood and serum parameters, and expression of cardiac and apoptotic genes compared to the control group. The ARE cotreatment significantly reduced the increase in serum transaminases, creatine kinase, and lactate dehydrogenase levels induced by DM. ARE facilitated the regain of electrolyte (sodium, potassium, chloride) homeostasis and antioxidants such as catalase, superoxide dismutase, glutathione peroxidase, and glutathione in DM-exposed fish. The cardiac histology exhibited loose separation of the cardiomyocytes and myofibrillar loss in the DM group which was ameliorated in the DM-ARE cotreatment group. Significant modulations were observed in the expression of cardiac-specific genes (gata4, myh6, tnT, cox1) and apoptosis signaling genes and proteins (HSP70, bax, bcl-2, caspase3), in the cotreatment group compared to the DM-exposed group. The current study suggests that ARE possesses potential cardioprotective properties that are effective in mitigating the toxic effects induced by DM via ameliorating oxidative stress, electrolyte imbalance, and apoptosis in tilapia.

A review of cumulative toxic effects of environmental endocrine disruptors on the zebrafish immune system: Characterization methods, toxic effects and mechanisms

Environmental endocrine disrupting chemicals (EDCs), are a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Currently, in addition to neurological, endocrine, developmental and reproductive toxicity, ecotoxicology studies on immunotoxicity are receiving increasing attention. In this review, the composition of immune system of zebrafish, the common indicators of immunotoxicity, the immunotoxicity of EDCs and their molecular mechanism were summarized. We reviewed the immunotoxicity of EDCs on zebrafish mainly in terms of immune organs, immunocytes, immune molecules and immune functions, meanwhile, the possible molecular mechanisms driving these effects were elucidated in terms of endocrine disruption, dysregulation of signaling pathways, and oxidative damage. Hopefully, this review will provide a reference for further investigation of the immunotoxicity of EDCs.

Novel protective aspects of dietary polyphenols against pesticidal toxicity and its prospective application in rice-fish mode: A Review

The rice fish system represents an innovative and sustainable approach to integrated farming, combining rice cultivation with fish rearing in the same ecosystem. However, one of the major challenges in this system is the pesticidal pollution resulting from various sources, which poses risks to fish health and overall ecosystem balance. In recent years, dietary polyphenols have emerged as promising bioactive compounds with potential chemo-preventive and therapeutic properties. These polyphenols, derived from various plant sources, have shown great potential in reducing the toxicity of pesticides and improving the health of fish within the rice fish system. This review aims to explore the novel aspects of using dietary polyphenols to mitigate pesticidal toxicity and enhance fish health in the rice fish system. It provides comprehensive insights into the mechanisms of action of dietary polyphenols and their beneficial effects on fish health, including antioxidant, anti-inflammatory, and detoxification properties. Furthermore, the review discusses the potential application methods of dietary polyphenols, such as direct supplementation in fish diets or through incorporation into the rice fields. By understanding the interplay between dietary polyphenols and pesticides in the rice fish system, researchers can develop innovative and sustainable strategies to promote fish health, minimize pesticide impacts, and ensure the long-term viability of this integrated farming approach. The information presented in this review will be valuable for scientists, aqua-culturists, and policymakers aiming to implement eco-friendly and health-enhancing practices in the rice fish system.

Assessment of deltamethrin-induced DNA damage, neurotoxic and neuroimmune effects in the brain tissue of brown trout (Salmo trutta fario)

This study investigated the impact of deltamethrin (DM) toxicity on brown trout (Salmo trutta fario), examining its effects on the immune system, including the white blood cell (WBC), lymphocyte (Lym), total immunoglobulin (T. Ig), and lysozyme levels, as well as its neurotoxic consequences on the brain tissue. The neurotoxic effects encompassed oxidative stress, the activity of the antioxidant enzymes, such as the superoxide dismutase (SOD) and catalase (CAT), acetylcholinesterase (AChE) activity, and DNA damage using 8-hydroxy-2-deoxyguanosine (8-OHdG). The DM exposure led to elevated levels of malondialdehyde (MDA), and 8-OHdG, while concurrently causing a reduction in the AChE activity, protein and lipid content, WBC count, Lym, lysozyme activity, T. Ig levels, as well as the SOD and CAT levels in the brain tissues of groups 2 and 3 when compared to those in group 1. In summary, the findings of this study strongly indicate that DM induces DNA damage, immunotoxicity, and neurotoxicity in the brain tissue of brown trout, primarily due to the excessive production of reactive oxygen species (ROS). Moreover, the observed dose-dependent responses of DM to the environmental concentrations on all the investigated parameters suggest its potential utility in aquaculture risk assessment.

Effect of chronic deltamethrin exposure on brain transcriptome and metabolome of juvenile crucian carp

Deltamethrin (Del), a widely administered pyrethroid insecticide, has been established as a common contaminant of the freshwater environment and detected in many freshwater ecosystems. In this study, we investigated the changes in brain transcriptome and metabolome of crucian carp after exposure to 0.6 μg/L Del for 28 days. Elevated MDA levels and inhibition of SOD activity indicate damage to the antioxidant system. Moreover, a total of 70 differential metabolites (DMs) were identified using the liquid chromatography-mass spectrometry, including 32 upregulated and 38 downregulated DMs in the Del-exposed group. The DMs associated with chronic Del exposure were enriched in steroid hormone biosynthesis, fatty acid metabolism, and glycerophospholipid metabolism for prostaglandin G2, 5-oxoeicosatetraenoic acid, progesterone, androsterone, etiocholanolone, and hydrocortisone. Transcriptomics analysis revealed that chronic Del exposure caused lipid metabolism disorder, endocrine disruption, and proinflammatory immune response by upregulating the pla2g4, cox2, log5, ptgis, lcn, and cbr expression. Importantly, the integrative analysis of transcriptomics and metabolomics indicated that the arachidonic acid metabolism pathway and steroid hormone biosynthesis were decisive processes in the brain tissue of crucian carp after Del exposure. Furthermore, Del exposure perturbed the tight junction, HIF-1 signaling pathway, and thyroid hormone signaling pathway. Overall, transcriptome and metabolome data of our study offer a new insight to assess the risk of chronic Del exposure in fish brains.

Adverse effects of fenpropathrin on the intestine of common carp (Cyprinus carpio L.) and the mechanism involved

Fenpropathrin (FEN), a pyrethroid pesticide, is frequently detected in natural water bodies, unavoidable pose adverse effects to aquatic organisms. However, the harmful effects and potential mechanisms of FEN on aquatic species are poorly understood. In this study, common carp were treatment with FEN at 0.45 and 1.35 μg/L for 14 d, and the toxic effects and underlying mechanisms of FEN on the intestine of carp were revealed. RNA-seq results showed that FEN exposure cause a wide range of transcriptional alterations in the intestine and the differentially expressed genes were mainly enrichment in the pathways related to immune and metabolism. Specifically, FEN exposure induced pathological damage and altered submicroscopic structure of the intestine, elevated the levels of Bacteroides fragilis enterotoxin, altered the contents of claudin-1, occludin, and zonula occluden-1 (ZO-1), and causing injury to the intestinal barrier. In addition, inflammation-related index TNF-α in the serum and IL-6 in the intestinal tissues were generally increased after FEN exposure. Moreover, FEN exposure promoted an increase in reactive oxygen species (ROS), altered the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), upregulated the contents of malondialdehyde (MDA) in the intestines. The apoptosis-related parameter cytochrome c, caspase-9, and caspase-3 were significantly altered, indicating that inflammation reaction, oxidative stress, and apoptosis may be involved in the toxic mechanism of FEN on carp. Moreover, FEN treatment also altered the intestinal flora community significantly, which may affect the intestinal normal physiological function and thus affect the growth of fish. Overall, the present study help to clarify the intestinal reaction mechanisms after FEN treatment, and provide a basis for the risk assessment of FEN.

Flunitrazepam and its metabolites compromise zebrafish nervous system functionality: An integrated microbiome, metabolome, and genomic analysis

The psychotropic drug flunitrazepam (FLZ) is frequently detected in aquatic environments, yet its neurotoxicity to aquatic organisms has not received sufficient attention. In this study, microbiome, metabolome, and genome analyses were conducted to study the effects of FLZ and its metabolite 7-aminoflunitrazepam (7-FLZ) on the zebrafish nervous system and understand their toxic mechanisms. The results demonstrated that drug exposure induced gut dysbiosis, decreased short-chain fatty acids and promoted the production of lipopolysaccharides (LPS). LPS entered the brain and interacted with Toll-like receptors to cause neuroinflammation by upregulating the expression of proinflammatory cytokines TNFα and NF-κB. The increased ratio of S-adenosylmethionine to S-adenosylhomocysteine in brain tissues indicated abnormal expression of Dnmt1 gene. Whole-genome bisulfite sequencing displayed an increase in differentially methylated regions (DMRs) associated-genes and pertinent biological pathways encompassed the MAPK signaling pathway, calcium signaling pathway, and Wnt signaling pathway. Correlation analysis confirmed connections between gut microbiota, their metabolites, inflammatory factors, and DNA methylation-related markers in brain tissue. These findings indicate that while the toxicity is somewhat reduced in metabolized products, both FLZ and 7-FLZ can induce DNA methylation in brain tissue and ultimately affect the biological function of the nervous system by disrupting gut microbiota and their metabolites.

The role of marine pollution on the emergence of fish bacterial diseases

Marine pollution and bacterial disease outbreaks are two closely related dilemmas that impact marine fish production from fisheries and mariculture. Oil, heavy metals, agrochemicals, sewage, medical wastes, plastics, algal blooms, atmospheric pollutants, mariculture-related pollutants, as well as thermal and noise pollution are the most threatening marine pollutants. The release of these pollutants into the marine aquatic environment leads to significant ecological degradation and a range of non-infectious disorders in fish. Marine pollutants trigger numerous fish bacterial diseases by increasing microbial multiplication in the aquatic environment and suppressing fish immune defense mechanisms. The greater part of these microorganisms is naturally occurring in the aquatic environment. Most disease outbreaks are caused by opportunistic bacterial agents that attack stressed fish. Some infections are more serious and occur in the absence of environmental stressors. Gram-negative bacteria are the most frequent causes of these epizootics, while gram-positive bacterial agents rank second on the critical pathogens list. Vibrio spp., Photobacterium damselae subsp. Piscicida, Tenacibaculum maritimum, Edwardsiella spp., Streptococcus spp., Renibacterium salmoninarum, Pseudomonas spp., Aeromonas spp., and Mycobacterium spp. Are the most dangerous pathogens that attack fish in polluted marine aquatic environments. Effective management strategies and stringent regulations are required to prevent or mitigate the impacts of marine pollutants on aquatic animal health. This review will increase stakeholder awareness about marine pollutants and their impacts on aquatic animal health. It will support competent authorities in developing effective management strategies to mitigate marine pollution, promote the sustainability of commercial marine fisheries, and protect aquatic animal health.

Trimethyltin chloride induces apoptosis and DNA damage via ROS/NF-κB in grass carp liver cells causing immune dysfunction

Trimethyltin chloride (TMT), a common component in fungicides and plastic stabilizers, presents environmental risks, particularly to fish farming. The precise toxicological mechanisms of TMT in L8824 grass carp liver cells remain undefined. Our study investigates TMT's effects on these cells, focusing on its potential to induce hepatotoxicity via oxidative stress and NF-κB pathway activation. First, we selected 0, 3, 6, and 12 μM as the challenge doses, according to the inhibitory concentration of 50% (IC50) of TMT. Our results demonstrate that TMT decreases cell viability dose-dependently and triggers oxidative stress, as evidenced by increased ROS staining and MDA content. Concurrently, it inhibited the antioxidant activities of T-AOC, T-SOD, CAT, and GSH. The activation of the NF-κB pathway was confirmed by gene expression changes. Furthermore, we observed an increase in cell apoptosis rate by AO/EB staining and cell flow cytometry, and the downregulation of Bcl-2 and the upregulation of Bax, Cytc, Caspase-9, and casp3 verified that TMT passed through the BCL2/BAX/casp3 pathway induces apoptosis. DNA damage was validated by the comet assay and γH2AX gene overexpression. Lastly, our data showed increased expression of TNF-α, IL-1β, IL-6, and INF-γ and decreased antimicrobial peptides, validating immune dysfunction. In conclusion, our findings establish that TMT induces apoptosis and DNA damage via ROS/NF-κB in grass carp liver cells, causing immune dysfunction. This study provides novel insights into the toxicology research of TMT and sheds light on the immunological effects of TMT toxicity, enriching our understanding of the immunotoxicity of TMT on aquatic organisms and contributing to the protection of ecosystems.

Conventional Anthelmintic Concentration of Deltamethrin Immersion Disorder in the Gill Immune Responses of Crucian Carp

Current treatment strategies for parasitic infectious diseases in crucian carp primarily rely on chemotherapy. As a commonly used antiparasitic agent, deltamethrin (DEL) may have the potential adverse effects on external mucosa of fish such as gills. In this study, 180 healthy juvenile crucian carp (Carassius auratus) (average weight: 8.8 ± 1.0 g) were randomly divided into three groups for 28 days, which were immersed in 0 μg/L, 0.3 μg/L, and 0.6 μg/L of DEL, respectively. The results of histological analysis revealed that severe hyperplasia in the secondary lamellae of gills was observed, and the number of goblet (mucus-secreting) cells increased significantly after DEL immersion. TUNEL staining indicated that the number of apoptotic cells increased in crucian carp gill. At the molecular level, the mRNA expression analysis revealed significant upregulation of apoptosis (caspase 3, caspase 8, and bax), autophagy (atg5 and beclin-1), and immune response (lzm, muc5, il-6, il-8, il-10, tnfα, ifnγ, tgfβ, tlr4, myd88, and nf-kb), whereas tight junction-related genes (occludin and claudin12) were downregulated after DEL immersion, suggesting that DEL immersion altered innate immunity responses and promoted mucus secretion. Moreover, tandem mass tag (TMT)-based proteomics revealed that a total of 428 differentially expressed proteins (DEPs) contained 341 upregulated DEPs and 87 downregulated DEPs with function annotation were identified between the control and DEL groups. Functional analyses revealed that the DEPs were enriched in apoptotic process, phagosome, and lysosome pathways. Additionally, DEL immersion also drove gill microbiota to dysbiosis and an increase in potentially harmful bacteria such as Flavobacterium. Overall, this study showed that DEL elicited shifts in the immune response and changes in the surface microbiota of fish. These results provide new perspectives on the conventional anthelmintic concentration of DEL immersion disorder of the gill immune microenvironment in crucian carp and theoretical support for future optimization of their practical application.

Efficiency of hematological, enzymological and oxidative stress biomarkers of Cyprinus carpio to an emerging organic compound (alphamethrin) toxicity

Alphamethrin is one of the extensively used pyrethroids. Its non-specific mode-of-action might affect the non-target-organisms. Its toxicity data on aquatic organisms are lacking. We determined the toxicity (35 days) of alphamethrin (0.6µg/L and 1.2µg/L) on non-target-organisms by evaluating the efficiency of hematological, enzymological and antioxidants biomarkers of Cyprinus carpio. Compared with the control group, the efficiency of the biomarkers studied was significantly (p<0.05) impaired in the alphamethrin groups. Alphamethrin-toxicity altered hematology, transaminases and the potency of LDH of fish. ACP and ALP activity and biomarkers of oxidative stress in the gills, liver and muscle tissues were affected. IBRv2 index reveals that the biomarkers were inhibited. The observed impairments were the toxicity effects of alphamethrin with respect to concentration and time. The effectiveness of biomarkers for alphamethrin toxicity was like the toxicity data available on other banned insecticides. Alphamethrin could cause multiorgan toxicity on aquatic organisms at µg/L level.

Modulatory effect of thymol on the immune response and susceptibility to Aeromonas hydrophila infection in Nile tilapia fish exposed to zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO-NPs) have many exciting properties that make their use in a continuous increase in various biomedical, industrial, and agricultural applications. This is associated with accumulation in the aquatic ecosystems and fish exposure with consequent deleterious effects. To determine the potential of thymol to counteract the immunotoxic effects of ZnO-NPs, Oreochromis niloticus was exposed to ZnO-NPs (⅕ LC₅₀ =1.14 mg/L, for 28 days) with or without feeding a thymol-incorporated diet (1 or 2 g/kg diet). Our data demonstrated a reduction of aquaria water quality, leukopenia, and lymphopenia with a decrease in serum total protein, albumin, and globulin levels in exposed fish. At the same time, the stress indices (cortisol and glucose) were elevated in response to ZnO-NPs exposure. The exposed fish also revealed a decline in serum immunoglobulins, nitric oxide, and the activities of lysozyme and myeloperoxidase, in addition to reduced resistance to the Aeromonas hydrophila challenge. The RT-PCR analysis showed downregulation of antioxidant (SOD) superoxide dismutase and (CAT) catalase gene expression in the liver tissue with overexpression of the immune-related genes (TNF-α and IL-1β). Importantly, we found that thymol markedly protected against ZnO-NPs-induced immunotoxicity in fish co-supplemented with thymol (1 or 2 g/kg diet) in a dose-dependent manner. Our data confirm the immunoprotective and antibacterial effects of thymol in ZnO-NPs exposed fish, supporting the potential utility of thymol as a possible immunostimulant agent.

Integrative time series of cellular, humoral and molecular response revealed immunotoxicity of bifenthrin to Chinese rare minnow (Gobiocypris rarus) following Pseudomonas fluorescens challenge

Bifenthrin is a common pesticide that is widespread in aquatic environments. Although it has been shown to be toxic to aquatic organisms, its immunotoxicity and mechanism are unclear. Herein, we reported the immunotoxicity of bifenthrin on adult Chinese rare minnow (Gobiocypris rarus) after 28 days of exposure to different concentrations of bifenthrin (0.1, 0.3, and 1.0 μg/L) and 36-h Pseudomonas fluorescens challenge. Bifenthrin inhibited the fish humoral immune response to bacteria by altering the lymphocyte and neutrophil ratios and decreasing the production of lysozyme, complement component 3, immunoglobulin M, and C-reactive protein, particularly were 1.0 μg/L. Bifenthrin caused intestinal damage and significantly reduced the volume of intestinal mucus at 12 and 36 hours postinjection (hpi) (p < 0.05). Moreover, 1.0 μg/L bifenthrin significantly increased the fish mortality and bacterial loads at 12 and 36 hpi (p < 0.05). RNA-seq analysis revealed several enriched genes involved in pathogen attachment and recognition, inflammatory responses, and complement system at the early-to-mid stage of infection (4-12 hpi). Overall, our results corroborated that bifenthrin induced immunotoxicity in Gobiocypris rarus, resulting in immune dysfunction of fish and increasing their sensitivity to bacterial infection and accelerating mortality. Moreover, 4-12 hpi was better than 36 hpi for analyzing immune responses against pathogen infection in fish exposed to bifenthrin.

Redox Status, Immune Alterations, Histopathology, and Micronuclei Induction in Labeo rohita Dwelling in Polluted River Water

In this study, we measured various parameters of oxidative stress, immune response, and abnormalities in the erythrocyte nucleus of Labeo rohita inhabiting the polluted Kshipra River, India. The river water contains heavy metals in this order: Ni > Fe > Cd > Cr > Mn > Zn > Cu. Fe showed the highest accumulation in gills, liver, and gut, whereas Ni (gills and gut) and Cd (liver) were lowest accumulated. The superoxide dismutase (SOD) and catalase (CAT) were found to be increased significantly (p < 0.05) in the gills (SOD: 211%; CAT: 150%), liver (SOD: 447%; CAT: 304%), and gut (SOD: 98.11%; CAT: 58.69%) in comparison with the reference fish. However, glutathione S transferase (GST) showed significantly (p < 0.05) higher activity in the gills (25.5%) but lower activity in the liver (- 49.22%) and the gut (- 30.57%). Moreover, reduced glutathione (GSH) decreased significantly (p < 0.05) in the gills (- 46.66%), liver (- 33.20%), and gut (- 39.87%). Despite the active response of the antioxidant enzymes, the highest lipid peroxidation was observed in the liver (463%). The effect of heavy metals was also observed on the immunity of the fish, causing immunosuppression as evident by significantly (p < 0.05) lower values of acid phosphatase (- 50%), myeloperoxidase (- 48.33%), and nitric oxide synthase (- 50%) in serum. Histopathological findings showed gill lamellae shortening, hyperplasia, club-shaped lamellar tip in exposed gills and necrosis, vacuolization, and pyknosis in the exposed liver. Furthermore, polluted river water was also found to induce micronuclei (2.1%) and lobed nuclei (0.72%) in erythrocytes (0.65%). These results indicate the potential of heavy metal-induced oxidative stress and other forms of stress in inhabiting fish, highlighting the need to control the pollution of this river water.

Acute deltamethrin exposure induces oxidative stress, triggers endoplasmic reticulum stress, and impairs hypoxic resistance of crucian carp

Deltamethrin (Del) has been widely used for effectively controlling ectoparasites of crucian carp and was also strictly prohibited in a hypoxic environment. A previous study indicated that Del exposure causes gill injury in Carassius auratus, which is associated with oxidative stress and endoplasmic reticulum stress (ER stress), but the precise mechanism is not well understood. Here, crucian carp were exposed to Del (0.61, 1.22, 2.44, 4.88 μg/L) for 24 h and then subjected to acute hypoxia challenge (1.0 mg/L) for 24 h. The results revealed that acute exposure to Del notably increased MDA content but markedly decreased CAT activities. Moreover, the T-AOC and SOD activities first increased and then decreased in the 4.88 μg/L Del group. Likewise, the mRNA levels of Nrf2 signaling and its target genes (ho-1, mt, sod, cat, and gpx1) were significantly downregulated in the high concentration exposure groups, while the mRNA levels of keap1 showed the opposite change trend. Meanwhile, Del exposure evoked the PERK-ATF4-CHOP and IRE1 signaling pathways and triggered ER stress in a dose-dependent manner in crucian carp. Importantly, we found that Del exposure significantly decreased the survival rate of crucian carp after hypoxia challenge by reducing oxygen uptake, modifying energy metabolism, and promoting lactate accumulation. Additionally, Del exposure aggravated gill damage and apoptosis under hypoxic stress, which was confirmed by histological assays. Collectively, we inferred that acute exposure to deltamethrin induces oxidative stress and ER stress and impairs hypoxic resistance of crucian carp.

Tannic acid antagonizes atrazine exposure-induced autophagy and DNA damage crosstalk in grass carp hepatocytes via NO/iNOS/NF-κB signaling pathway to maintain stable immune function

Atrazine (ATR) is a herbicide widely used in grass crops. The pollution of the soil and water environment is extremely harmful to aquatic animals and their offspring. iNOS/NO upregulation, DNA damage and cellular autophagy affect the immune function of fish liver cells. The effects of ATR at exposure doses on grass carp hepatocytes in terms of autophagy and DNA damage effects in genotoxicity, as well as the antagonistic effects of TAN on the above phenotypes and the internal mechanisms are not known. Therefore, we constructed control (Con group), ATR exposure (ATR group), TAN exposure (TAN group) and mixed group (ATR + TAN group) models on grass carp hepatocytes. Validation was performed by comet assay, MDC staining, qRT-PCR and protein blotting assay as well as iNOS/NO indicator levels and expression of immune factors as these experimental methods. Our data indicate that iNOS/NO assay kit measured that ATR treatment resulted in a significant increase in iNOS/NO activity and levels in grass carp hepatocytes (p < 0.05). We also found that NO/iNOS/NF-κB pathway genes were significantly activated (p < 0.05) at the exposure dose of ATR (3 μg mL-1). In addition, the proportion of cells that died due to DNA damage, autophagy, and immunotoxic effects was significantly increased at the exposure dose of ATR. Comet assay protein blotting detected increased DNA damage in cells at the ATR exposure dose (p < 0.05). MDC staining and qRT-PCR and protein blotting to detect the proportion of autophagic cells and autophagy-related genes also appeared upregulated at the exposed dose of ATR (p < 0.05). In brief, this study showed that ATR exposure caused cellular DNA damage and autophagy via the NO/iNOS/NF-κB axis, which led to immunotoxic effects and eventual death of grass carp hepatocytes. The present study facilitates the demonstration of the molecular mechanism of TAN alleviation of ATR cytotoxicity from the perspective of NO-mediated iNOS/NF-κB axis. It provides insights into the protection of farmed fish from agricultural contaminants and opens up new horizons in the use of natural plant-derived monomers for the clinical treatment of antagonistic triazine pesticide poisoning.

Environmental concentrations of 2, 4-DTBP cause immunotoxicity in zebrafish (Danio rerio) and may elicit ecological risk to wildlife

Synthetic phenolic antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) has gained growing concerns due to relatively high concentrations in aquatic ecosystems. There are, however, significant knowledge gaps regarding its potential toxicity to aquatic organisms. In this study, zebrafish (Danio rerio) larvae were exposed to 0.01, 0.1, or 1 μM 2,4-DTBP for 6 d. Transcriptomic analysis of larvae revealed that biological processes related to anti-inflammatory function of macrophage M2 lineage were inhibited by 0.01 μM 2,4-DTBP. Decreases of transcripts related to the IL1B-MYD88-NF-κB pathway (i.e., il1b, il1rl1, myd88, irak4, irak1, traf6, ikbkg, nfkbia, nfkb) and protein levels of NF-κB in larvae intestine confirmed anti-inflammatory effects of 2,4-DTBP. Subsequently, larvae exposed to 2,4-DTBP were challenged with E. coli and showed higher survival rate, suggesting sustained activation of inflammation via LPS can be attenuated by 2,4-DTBP. Moreover, histological examination revealed that intestine barrier was compromised and there was an imbalance of intestine macrophage homeostasis. Food intake was also reduced following exposure to 0.1 and 1 μM 2,4-DTBP. In addition, a risk assessment revealed that 2,4-DTBP in surface water pose low to high ecological risks to aquatic organisms. Taken together, exposure to environmentally relevant concentrations of 2,4-DTBP could negatively affect immune response in zebrafish and may elicit ecological risk in fish population.

Deposition of polystyrene microplastics on bare or biofilm-coated silica analysed via QCM-D

The mobility of microplastics (MPs) in aqueous media is closely related to their environmental risk. The naturally occurring silica substrate surface in the aquatic environment is easily colonized by microorganisms and forms a biofilm, which may affect the migration and distribution of MPs. Herein, a typical MP, polystyrene (PS), and Pseudomonas fluorescens (P. fluorescens) biofilms were selected to study the deposition and release of pristine or ultraviolet (UV)-aged PS MPs on silica and biofilms under different ionic strengths using a quartz crystal microbalance dissipation (QCM-D) system. Statistical analyses of the deposition experiments revealed a significant impact of P. fluorescens biofilms on deposition (p = 0.0042). The deposition rate of weathered MPs on the biofilms was 4.0 ± 0.1 to 16.3 ± 0.6 times that on silica. A release experiment revealed that the biofilm reduced the release fraction (f_r) of weathered MPs by 34.5 ± 0.3 % compared to bare silica. In addition, the UV-ageing treatment reduced the deposition mass of MPs on the surface of silica by 27.6 ± 0.21 % compared to pristine microspheres. The analysis of the deposition mechanism revealed that the promotion and inhibition of biofilm or UV-ageing treatment on the deposition of microspheres could be attributed to the non-Derjaguin-Landau-Verwey-Overbeek (DLVO) force and the decreased electrostatic repulsion or the increased hydration repulsion, respectively.

Integrated biomarker approach strongly explaining in vivo sub-lethal acute toxicity of butachlor on Labeo rohita

Butachlor herbicide belongs to the family of chloroacetanilide group, widely used for control of grass and broadleaf weeds in paddy fields however, its repeated application may result in aquatic pollution. Butachlor residue has been detected in aquatic environments, which may produce toxic effects on non-target organisms including fish. Keeping this in mind, the present study was designed to estimate the LC₅₀ of butachlor (Shaktiman®), and to evaluate the sub-lethal toxicity at two concentrations (12.42 μg L^-1 and 62.10 μg L^-1) in Labeo rohita for a period of 24, 48, and 72 h. Fish exposed to butachlor reduced the counts of red blood cells (RBC), haemoglobin (HGB), hematocrit (HCT), and white blood cells (WBC). A significant (p < 0.05) increase in the antioxidant enzyme (superoxide dismutase-SOD, glutathione-s-transferase-GST), and hepatic enzyme (glutamate-oxaloacetate transaminase-GOT, glutamate-pyruvate transaminase-GPT) were noticed in butachlor exposed fish. Heat shock protein 70 (HSP70) and HSP90 in gill; cortisol, protein, albumin, globulin, and triglyceride in serum were increased upon exposure of butachlor. On the contrary, complement 3 (C3) and immunoglobulin (IgM) in serum was found to be decreased compared to control fish. The findings thus suggest that the fish upon exposure to butachlor disrupts the biomarkers which ultimately leads to growth retardation in fish.

Asparagus racemosus improves immune-related parameters in Nile tilapia (Oreochromis niloticus) and mitigates deltamethrin-induced toxicity

Deltamethrin (DM) is one of the most toxic but widely used pyrethroid insecticides. Even though a non-target animal, fish are at high risk as they are deficient in the enzyme system that hydrolyses pyrethroids. Enhancing the immune system is a potential method in preventing fish diseases. The present investigation aims to study the modulations in the immune response-related parameters in Oreochromis niloticus that were exposed to DM, by dietary supplementation of aqueous root extract of Asparagus racemosus (ARE). The experiment compared fish in control, DM (1 μg/L) exposed (added to water), ARE (10 g, 20 g, and 30 g ARE/kg of feed) supplemented, and DM-ARE cotreated groups. After 21 days of experimental period, serological, histopathological, and immune response related-gene and protein analysis were carried out. The DM-ARE cotreated group showed significant increase in weight gain, specific growth rate, and decreased feed conversion ratio compared to the DM exposed group. The ARE cotreatment could significantly revert the alteration induced by DM in lysozyme, respiratory burst, myeloperoxidase, C-reactive protein, glucose, cortisol, total protein, albumin, and triglyceride levels. The liver histopathology showed membrane breakage, severe necrosis, infiltration of inflammatory cells, melano-macrophages, and nuclear atrophy, and the kidney showed tubular necrosis, hematopoietic necrosis, Bowman's capsule edema, and glomerulus degeneration in DM exposed group. In ARE cotreated group, the liver showed regenerative cellular changes and only mild to moderate cellular damages, and the kidney tubules and glomerulus had intact structure. ARE discernibly regulated the expression of immune-related genes and proteins (IgM, TNFα, IFN-γ, IL-1β, and IL-8) in fish. The DM-ARE cotreated groups showed reduced cumulative mortality and higher relative percent survival on experimental challenge with Aeromonas hydrophila compared to the DM group. Thus, ARE possess protective potential against DM-induced toxicity, and can be used as a cost-effective technique in aquafarming.

Environmentally relevant concentrations of fenvalerate induces immunotoxicity and reduces pathogen resistance in Chinese rare minnow (Gobiocypris rarus)

Fenvalerate is a broadly used type II pyrethroid with a potential toxic effect in fish. However, information on the immunotoxicity of fenvalerate in fish is scarce. Here, to discover the immunotoxicity of fenvalerate and its underlying mechanism in fish, adult Chinese rare minnow was exposed to fenvalerate at 0, 0.3, 1, and 3 μg/L for 28 days and then subjected to Pseudomonas fluorescens (P. fluorescens) challenge. Fenvalerate induced significant pathological changes, with disintegration of cell boundaries in the intestine, epithelial hyperplasia in gills, and vacuolation of hepatocytes at 3 μg/L treatment. Additionally, the pathological characteristics were more serious during P. fluorescens infection after fenvalerate exposure. A significant increase in neutrophil counts was observed after 3 μg/L fenvalerate exposure for 28 days (p < 0.05), whereas significantly increased monocyte and neutrophil counts and greatly decreased lymphocyte counts were detected at 24 h post-injection (hpi) with P. fluorescens (p < 0.05). Furthermore, obvious decreases in LYS, IgM, ALP, and C3 levels were detected in plasma after 3 μg/L fenvalerate exposure for 28 days, which was consistent with the results at 24 and 48 hpi. Notably, fish exposed to fenvalerate suppressed the transcription of TLR-NF-κB signaling pathway-relevant genes in response to P. fluorescens, accompanied by high mortalities and bacterial loads. Therefore, our results demonstrate that fenvalerate at environmentally relevant concentrations caused immunotoxicity in fish. This study highlights the importance of considering the combined effects of chemicals and pathogens to refine our ability to predict the effects of environmental contaminants on aquatic organisms.

Dietary α-lipoic acid alleviates deltamethrin-induced immunosuppression and oxidative stress in northern snakehead (Channa argus) via Nrf2/NF-κB signaling pathway

The goal of the study was to determine the ameliorative effects of dietary alpha-lipoic acid (α-LA) on deltamethrin (DEL)-induced immunosuppression and oxidative stress in northern snakehead (Channa argus). The northern snakeheads (15.38 ± 0.09 g) were exposed to DEL (0.242 μg/L) and fed with diets supplemented α-LA at 300, 600, and 900 mg/kg. After the 28-day exposure test, we obtained the following results: i) α-LA alleviates DEL-induced liver injury by reversing the increase of the serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels and liver cytochrome P450 enzymes (Cytochrome P450 (cyp)1a and cyp1b) expression levels. ii) α-LA can reverse the DEL-induced reduction of serum complement 4 (C4), C3, immunoglobulin M (IgM), and lysozyme (LYS) levels and the increase of liver and intestine nuclear factor kappa B (nf-κb) p65, tumor necrosis factor (tnf)-α, interleukin (il)-1β, il-8, and il-6 gene expressions, while il-10 expression levels showed the opposite result. iii) α-LA reversed the reduction of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione-S-transferase (GST) and glutathione peroxidase (GSH-Px) levels in the liver and intestine induced by DEL, while malondialdehyde (MDA) showed the opposite result. iv) α-LA reversed the reduction of Cu/Zn sod, nuclear factor erythroid 2-related factor 2 (nrf2), NAD (P)H: quinone oxidoreductase (nqo)1, and heme oxygenase (ho)-1 antioxidant gene expression levels in the liver and intestine induced by DEL. Therefore, our study indicated that optimal α-LA (600 mg/kg) could attenuate DEL-induced toxicity (including liver damage, immunotoxicity, and oxidative stress) in northern snakehead via Nrf2/NF-κB signaling pathway. This is the first research that explores the alleviated effects of α-LA on DEL-induced toxicity damage in fish. This study provides a positive measure to reduce the toxicity damage caused by DEL to aquatic animals, and provides a theoretical basis for exploring the regulation mechanism of α-LA in toxic substances.

Chronic exposure to deltamethrin disrupts intestinal health and intestinal microbiota in juvenile crucian carp

The indiscriminate use of deltamethrin in agriculture and aquaculture can lead to residues increased in many regions, which poses negative impacts on intestinal health of aquatic organisms. Although the potential toxicity of deltamethrin have recently attracted attention, the comprehensive studies on intestinal injuries after chronic deltamethrin exposure remain poorly understood. Herein, in a 28-day chronic toxicity test, crucian carp expose to different concentrations of deltamethrin (0, 0.3, and 0.6 μg/L) were used as the research object. We found that the morphology changes and increased goblet cells in intestinal tissue, and the extent of tissue injury increased along with the increasing exposure dose of deltamethrin. Additionally, the genes expression of antioxidant activity (Cu/Zn superoxide dismutase (Cu-Zn SOD), glutathione peroxidase 1 (GPX1), and catalase (CAT)), inflammatory response (tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), and interleukin 1 beta (IL-1β)), and tight junctions (Claudin 12 (CLDN12), and tight junction protein 1 (ZO-1)) dramatically increased. Meanwhile, the apoptosis and autophagy process were triggered through caspase-9 cascade and autophagy related 5 (ATG5)- autophagy related 12 (ATG12) conjugate. Besides, chronic deltamethrin exposure increased the amount of Proteobacteria and Verrucomicrobiota, while decreased Fusobacteriota abundance, resulting in intestinal microbiota function disorders. In summary, our results highlight that chronic exposure to deltamethrin cause serious intestinal toxicity and results in physiological changes and intestinal flora disturbances.

Zinc alters behavioral phenotypes, neurotransmitter signatures, and immune homeostasis in male zebrafish (Danio rerio)

Anthropogenic activities discharge zinc into aquatic ecosystems, and the effects of long-term and low-concentration zinc exposure on fish behavior are unclear. We evaluated the behavior and physiology of male zebrafish (Danio rerio) after a 6-week exposure to 1.0 or 1.5 ppm (mg/L) zinc chloride. The exposure caused anxiety-like behaviors and altered the social preferences in both exposure groups. Analysis of transcriptional changes suggested that in the brain, zinc exerted heterogenetic effects on immune and neurotransmitter functions. Exposure to 1.0 ppm zinc chloride resulted in constitutive immune dyshomeostasis, while exposure to 1.5 ppm zinc chloride impaired the neurotransmitter glutamate. In the intestine, zinc dysregulated self-renewal of intestinal cells, a potential loss of defense function. Moreover, exposure to 1.5 ppm zinc chloride suppressed intestinal immune functions and dysregulated tyrosine metabolism. These behavioral alterations suggested that the underlying mechanisms were distinct and concentration-specific. Overall, environmental levels of zinc can alter male zebrafish behaviors by dysregulating neurotransmitter and immunomodulation signatures.

RNA-Seq and 16S rRNA Analysis Revealed the Effect of Deltamethrin on Channel Catfish in the Early Stage of Acute Exposure

Deltamethrin (Del) is a widely used pyrethroid insecticide and a dangerous material that has brought serious problems to the healthy breeding of aquatic animals. However, the toxicological mechanisms of Del on channel catfish remain unclear. In the present study, we exposed channel catfish to 0, 0.5, and 5 μg/L Del for 6 h, and analyzed the changes in histopathology, trunk kidney transcriptome, and intestinal microbiota composition. The pathological analyses showed that a high concentration of Del damaged the intestine and trunk kidney of channel catfish in the early stage. The transcriptome analysis detected 32 and 1837 differentially expressed genes (DEGs) in channel catfish trunk kidneys after exposure to 0.5 and 5 μg/L Del, respectively. Moreover, the KEGG pathway and GO enrichment analyses showed that the apoptosis signaling pathway was significantly enriched, and apoptosis-related DEGs, including cathepsin L, p53, Bax, and caspase-3, were also detected. These results suggested that apoptosis occurs in the trunk kidney of channel catfish in the early stage of acute exposure to Del. We also detected some DEGs and signaling pathways related to immunity and drug metabolism, indicating that early exposure to Del can lead to immunotoxicity and metabolic disorder of channel catfish, which increases the risk of pathogenic infections and energy metabolism disorders. Additionally, 16S rRNA gene sequencing showed that the composition of the intestinal microbiome significantly changed in channel catfish treated with Del. At the phylum level, the abundance of Firmicutes, Fusobacteria, and Actinobacteria significantly decreased in the early stage of Del exposure. At the genus level, the abundance of Romboutsia, Lactobacillus, and Cetobacterium decreased after Del exposure. Overall, early exposure to Del can lead to tissue damage, metabolic disorder, immunotoxicity, and apoptosis in channel catfish, and affect the composition of its intestinal microbiota. Herein, we clarified the toxic effects of Del on channel catfish in the early stage of exposure and explored why fish under Del stress are more vulnerable to microbial infections and slow growth.

Multi-biomarkers approach to assess the toxicity of novel insecticide (Voliam flexi®) on Clarias gariepinus: From behavior to immunotoxicity

This study was conducted to determine for the first time the immunological, histopathological, histochemical, and ultrastructural changes; hematological and biochemical alterations; and poikilocytosis induced in Clarias gariepinus by Voliam flexi® 40% WG (thiamethoxam + chlorantraniliprole). Beside control fish, juvenile C. gariepinus were subjected to three sublethal concentrations of Voliam flexi® (43.5, 87.5, and 175 mg/L) for 15 days. Voliam flexi® induced immunotoxic impairments in C. gariepinus, such as a decrease in some immunity variables (lysozyme and phagocyte activity, immunoglobulin concentration, and nitro blue tetrazolium level). It also caused an extreme increase in the levels of primary cytokines (interleukin-1β and IL-6), compared with the control. The toxic effects of Voliam flexi® increased gradually with the increasing concentrations tested. Histological examination of the liver demonstrated necrosis, vacuolated hepatocytes (fatty deposition), melanomacrophage centers, foci of inflammatory cells, congested and dilated blood sinusoids, hepatic degeneration, fibrosis increment (Sirius Red stain), and glycogen depletion, as well as cytopathological alterations. We conclude that the toxic effects of Voliam flexi® must be restricted or prevented by using control mechanisms in aquatic systems.

miRNAs: A potentially valuable tool in pesticide toxicology assessment-current experimental and epidemiological data review

miRNAs are responsible for the regulation of many cellular processes such as development, cell differentiation, proliferation, apoptosis, and tumor growth. Several studies showed that they can also serve as specific, stable, and sensitive markers of chemical exposure. In this review, current experimental and epidemiological data evidencing deregulation in miRNA expression in response to fungicides, insecticides or herbicides were analyzed. As shown by Venn's diagrams, miR-363 and miR-9 deregulation is associated with fungicide exposure in vitro and in vivo, while let-7, miR-155, miR-181 and miR-21 were found to be commonly deregulated by at least three different insecticides. Furthermore, let-7, miR-30, miR-126, miR-181 and miR-320 were commonly deregulated by 3 different herbicides. Notably, these 5 miRNAs were also found to be deregulated by one or more insecticides, suggesting their participation in the cellular response to pesticides, regardless of their chemical structure. All these miRNAs have been proposed as potential biomarkers for fungicide, insecticide, or herbicide exposure. These results allow us to improve our understanding of the molecular mechanisms of toxicity upon pesticide exposure, although further studies are needed to confirm these miRNAs as definitive (not potential) biomarkers of pesticide exposure.

Histopathology and transcriptome analysis reveals the gills injury and immunotoxicity in gibel carp following acute deltamethrin exposure

More and more evidences proved that deltamethrin (Del) exposure induced adverse effects and damaged immune function to the aquatic animals in the parasite killing process with increasing insecticide application. However, little is currently known of the negative effect on mucosal immunity, especially in gills tissue. Therefore, this study was aimed to reveal the tissue injury and immunotoxicity in the gill of gibel carp following acute deltamethrin exposure. The LC50 of deltamethrin on gibel carp at 96 h was determined to be 6.194 μg/L, and then juvenile gibel carp (Carassius auratus gibelio) (8.8 ± 1.0 g) were exposed to four Del exposure groups (0.61, 1.22, 2.44, and 4.88 μg/L) for 12 h and 24 h. We measured the lysozyme (LYZ) contents and myeloperoxidase (MPO) activities and found that with increased concentration of Del exposure, the LYZ contents were found to increase in the 1.22 μg/L Del group initially significantly and then gradually significantly decrease in the 4.88 μg/L Del group. And the activities of MPO were significantly lifted in a dose-dependent manner. The histological analysis showed that Del exposure caused serious desquamation and necrosis in the surface of epithelial cells, accompanied by interlamellar cellular mass degenerative. In addition, the mucous cells were significantly decreased in the high Del concentration group (2.44 μg/L and 4.88 μg/L Del group) by AB-PAS staining. Additionally, totally 2857 DEGs (including 1624 up-regulated and 1233 down-regulated genes) were identified between the control group and 4.88 μg/L Del exposure group using transcriptional analysis. Among these, some genes involved in innate immune molecules, complement activation, apoptosis-related molecules, cytokine, and adaptive immune molecules, were also down-regulated. Importantly, we found immune system process and tumor necrosis factor receptor (superfamily) binding pathways were downregulated based on the GO and KEGG enrichment analysis. Meanwhile, we detected the expression of pro-inflammatory cytokines (TNF-α, IFN-γ, IL-1β, and IL-8), anti-inflammatory cytokines (TGF-β), LYZ, IgM, and Hsp70 in the gills tissue at 12 h and 24 h after Del exposure, which were consistent with our sequencing results. Collectively, these results demonstrated that the gills injury and immunotoxicity were induced by Del exposure and provided novel insight for explaining to some extent why Del-exposure fish are more susceptible to concurrent or secondary viral or bacterial infections.

Aquatic toxicity and aquatic ecological risk assessment of wastewater-derived halogenated phenolic disinfection byproducts

Increasing number of wastewater-derived aliphatic and phenolic disinfection byproducts (DBPs) were discharged into aquatic environment with the discharge of disinfected wastewater. However, the currently available aquatic toxicity data and the aquatic ecological risk information of them are limited, especially for wastewater-derived phenolic DBPs. In this study, we investigated the acute toxicity of 7 phenolic DBPs that selected from the typical five groups of phenolic DBPs (2,4,6-trihalo-phenols, 2,6-dihalo-4-nitrophenols, 3,5-dihalo-4-hydroxybenzaldehydes, 3,5-dihalo-4-hydroxybenzoic acids and halo-salicylic acids) and 4 aliphatic DBPs to Gobiocypris rarus and also assessed their potential aquatic ecological risk. Experimental results indicated that the half lethal concentration (LC₅₀) values of 2,4,6-trihalo-phenols and 2,6-dihalo-4-nitrophenols ranged from 1 to 10 mg/L; While that of 3,5-dihalo-4-hydroxybenzaldehydes was between 10 and 100 mg/L, and 3,5-dihalo-4-hydroxybenzoic acids and halo-salicylic acids was >100 mg/L. The toxicity mode of action (MOA) identification results from three methods suggested that no clear and consistent MOA were obtained for those 11 DBPs currently. The species-specific aquatic toxicity analysis results highlighted that no aquatic species would be considered as the most sensitive species for all 11 DBPs. However, crustacean and fish were more sensitive than that of algae for most of tested compounds. Lastly, the aquatic ecological risk assessment results of those 11 DBPs revealed that all 7 phenolic and 2 aliphatic DBPs (2-bromoacetamide and bromodichloromethane) had low aquatic ecological risk, while dichloroacetic acid and dibromoacetonitrile had high aquatic ecological risk. The low environmental concentration was the main reason why high toxic phenolic DBPs (2,4,6-trihalo-phenols and 2,6-dihalo-4-nitrophenols) exhibited low ecological risk. Their ecological risk may increase with the increases of corresponding environmental concentration. Thus, more efforts should be made to determine other potential harmful effects of those high toxic phenolic DBPs and to minimize their potential ecological risk by taking appropriate measures.

Assessment of the effect of sub-lethal acute toxicity of Emamectin benzoate in Labeo rohita using multiple biomarker approach

Emamectin benzoate (EMB) is a potent neurotoxin agent, widely used for ectoparasites control in aquaculture, but their detailed toxicological implications in Labeo rohita are unknown. Thus, this study was conceptualized to determine the LC₅₀ and to investigate the effects of two sub-lethal concentrations 1/50th of 96 h LC₅₀ (1.82 μgL^-1) and 1/10thof 96 h LC₅₀ (9.1 μgL^-1) on hemato-immunological and biochemical responses in L. rohita (mean weight 25.54 ± 2.3 g and length 10.35 ± 2.4 cm) for a period of 24 h, 48 h, and 72 h. LC₅₀ of EMB were 163 μgL^-1, 112 μgL^-1, 99 μgL^-1 and 91 μgL^-1 at 24 h, 48 h, 72 h, and 96 h respectively. The safe limit at 96 h LC₅₀ of EMB was 2.30 μgL^-1. In EMB treated fish, red blood cells, white blood cells, hemoglobin, and hematocrit counts were reduced (p < 0.05) significantly. Superoxide dismutase (SOD) activity in the liver and kidney declined (p < 0.05) at 72 h while in gill and muscle the activity increased significantly. Glutathione-s-transferase (GST) activity in the liver, gill, and kidney increased (p < 0.05) while muscle decreased significantly. Catalase (CAT) activity in liver, gill, and muscle decreased while in kidney increases. Glutamic-oxaloacetic acid transaminase (GOT) activity and Glutamate pyruvate transaminase (GPT) activity were increased in liver, kidney, and muscle tissue. The change in serum triglycerides, serum protein level was noticed. The level of cortisol, heat shock protein 70 (HSP70), and HSP90 increased (p < 0.05) while the immunological responses like immunoglobulin M (IgM) and complement 3(C3) activity decreased (p < 0.05) in EMB exposed fish. Thus, EMB exposure at two sub-lethal concentrations in L. rohita induces several hemato-immuno, and biochemical alterations in blood, serum, and different organs. The overall result of the present study indicated that EMB is toxic to fish even for a short-term exposure and low doses, and therefore utmost caution should be taken to prevent their drainage into water bodies.

Estrogen receptor: A potential linker of estrogenic and dopaminergic pathways in zebrafish larvae following deltamethrin exposure

Deltamethrin (DM), a type II pyrethroid insecticide, is widely used to control agricultural pests. However, its excessive use exerts a detrimental effect on the ecological environment and human health, indicating the need to study its potential risks in detail. In the present study, zebrafish embryos were exposed to varying concentrations of DM (0.1, 1, 10, and 25 μg/L) for 96 h to assess the alterations in the transcript levels of proteins of the estrogenic and dopaminergic pathways. In addition, its effect on zebrafish locomotor activity was studied. The mRNA expression of cyp19a1b, erα, erβ2, fshr, gnrh2, gnrhr3, vtg3, dat, and dr1 significantly changed after exposing the embryos to DM. Deltamethrin at 10 and 25 μg/L significantly reduced the average swimming speed of zebrafish larvae. In addition, embryos injected with zebrafish estrogen receptor α (erα) and β (erβ) morpholinos and co-exposed to 25 μg/L DM for 96 h showed reduced expression of vtg3 mRNA compared to embryos exposed to 25 μg/L DM only. The locomotor activity of erα and erβ knockdown zebrafish following DM exposure was increased significantly when compared with that of larvae exposed to 25 μg/L DM only. Our results demonstrated that DM altered the locomotor activity of zebrafish larvae and the transcript levels of the components of estrogenic and dopaminergic pathways; erα and erβ knockdown weakened these effects.

Effects of acute deltamethrin exposure on kidney transcriptome and intestinal microbiota in goldfish (Carassius auratus)

As a widely used synthetic pyrethroid insecticide, deltamethrin (DM) causes serious health problems to aquatic organisms. However, the comprehensive understanding of the adverse effect of DM on aquatic organisms has received limited attention. In this study, goldfish (Carassius auratus) were exposed to 0 (control group), 0.2 and 2 µg/L DM for 96 h. The kidney transcriptome and intestinal microbiota were investigated. Comparative transcriptome analysis identified 270 and 711 differentially expressed genes (DEGs) in goldfish kidneys after exposure to 0.2 and 2 µg/L DM, respectively. KEGG pathway analysis revealed that the apoptosis pathway was markedly regulated and the regulation of programmed cell death was significantly enriched by the GO analysis. Several apoptosis-related genes including cathepsin L and cytochrome c were also detected. These results indicated that apoptosis occurred in the goldfish kidney after acute exposure to sublethal concentration of DM. Besides, some immune and drug metabolism-related DEGs were identified, indicating that exposure to DM caused immunotoxicity and metabolic disruption in goldfish. Additionally, 16 S rRNA gene sequencing analysis revealed a remarkable alteration in the composition of the intestinal microbial community of DM-treated goldfish. At the phylum level, the abundance of Proteobacteria, Firmicutes and Fusobacteria was increased, whereas the abundance of Bacteroidetes was reduced significantly after DM exposure. At the genus level, the abundance of Aeromonas, Cetobacterium, Dielma and Pseudorhodobacter was reduced, whereas Akkermansia was increased after DM exposure. In summary, exposure to DM could induce apoptosis and immunotoxicity in goldfish kidneys and affect the composition of the intestinal microbiota in goldfish. This study provides a comprehensive analysis of the adverse effect of DM exposure on the goldfish and will be helpful for understanding the toxicological mechanisms of DM in fish.

Toxicological effects of deltamethrin on quail cerebrum: Weakened antioxidant defense and enhanced apoptosis

Deltamethrin is the most common type II synthetic pyrethroid insecticide, and has posed widespread residues to environment. However, whether deltamethrin has potential toxic effects on quail cerebrum remains greatly obscure. Accordingly, we investigated the impact of chronic exposure to deltamethrin on oxidative stress and apoptosis in quail cerebrum. Quails upon 12-week exposure of deltamethrin (0, 15, 30, or 45 mg/kg body weight intragastric administration) were used as a cerebrum injury model. The results showed that deltamethrin treatment led to cerebral injury dose-dependently through the weakened antioxidant defense by downregulating nuclear factor erythroid-2-related factor 2 (Nrf2) and its downstream proteins levels and mRNA expression. Furthermore, deltamethrin treatment induced apoptosis in cerebrum by decreasing B-cell lymphoma gene 2 (Bcl-2) level, as well as increasing Jun N-terminal kinase3, caspase-3, and Bcl-2-associated X protein levels. Simultaneously, toll-like receptor 4 (TLR4) downstream inflammation-related genes or proteins were significantly up-regulated by deltamethrin dose-dependently. Altogether, our study demonstrated that chronic exposure to deltamethrin induces inflammation and apoptosis in quail cerebrums by promoting oxidative stress linked to inhibition of the Nrf2/TLR4 signaling pathway. These results provide a novel knowledge on the chronic toxic effect of deltamethrin, and establish a theoretical foundation for the evaluation of pesticide-induced health risk.

Immunotoxicological effects of insecticides in exposed fishes

Biologically active compounds used in agriculture that develop near aquatic environments easily spill into rivers or lakes. As a result, insecticides, herbicides and fungicides are observed worldwide in aquatic environments and accumulated in aquatic organism. Many insecticides, including organochlorine and organophosphate, have long been banned long ago because of their high persistence and non-target toxicity. However, previous studies have shown that persistent pesticides remain in aquatic organisms. The immune system is the first defense mechanism against exposure to persistent organic pollutants or pesticides that have been released into the aquatic environment. Many insecticides have been reported to cause immunotoxicity, which is represented by alteration of phagocytic and lysozyme activity. Recent studies show that immunotoxicity by insecticides exerts a more complex mechanism in fish. Insecticides induce immunotoxic effects, such as the release of inflammatory cytokines from head kidney macrophages and inhibition of immune cell proliferation in fish, which can lead to death in severe cases. Even currently used pesticides, such as pyrethroid, with low bioaccumulation have been shown to induce immunotoxicological effects in fish when exposed continuously. Therefore, this review describes the types and bioaccumulation of insecticides that cause immunotoxicity and detailed immunotoxicological mechanisms in fish tissues.

Short-term intake of deltamethrin-contaminated fruit, even at low concentrations, induces testicular damage in fruit-eating bats (Artibeus lituratus)

Deltamethrin (DTM) is a pyrethroid insecticide widely used for agricultural purposes. Exposure to DTM has proven to be harmful to humans, but whether low, environmental concentrations of this pesticide also poses a threat to wild mammals is still unknown. In Neotropical areas, bats play important roles in contributing to forest regeneration. We investigated the effects of DTM exposure on the reproductive function of male Neotropical fruit-eating bats (Artibeus lituratus), known for contributing to reforestation through seed dispersal in Neotropical Forests. Bats were assigned to 3 groups: control (fed with papaya); DTM2 (fed with papaya treated with DTM at 0.02 mg/kg) and DTM4 (fed with papaya treated with DTM at 0.04 mg/kg) for seven days. Bats from DTM2 and DTM4 groups showed increased testicular levels of nitric oxide and superoxide dismutase and catalase activities. The germinal epithelium from DTM4 bats showed non-viable cells and cell desquamation, indicating microscopic lesions and Leydig cells atrophy. Our results demonstrate the onset of cell degeneration that may affect the reproductive function in DTM exposed bats.

Polystyrene microplastics induce apoptosis via ROS-mediated p53 signaling pathway in zebrafish

Microplastic (MP) pollution is ubiquitous and has become an emerging threat to aquatic biota. Recent scientific reports have recorded their toxic impacts at the cellular and organism levels, but the underlying molecular mechanism of their toxicity remains unclear. The present study elucidates an array of molecular events underlying apoptosis in the gills of polystyrene microplastics (PS-MPs) exposed zebrafish (Danio rerio). PS-MPs at different concentrations (10 and 100 μg L^-1) induced the reactive oxygen species (ROS) generation, in turn affecting the oxidative and immune defense mechanism. The expression profile of antioxidant genes cat, sod1, gpx1a and gstp1 were altered significantly. PS-MPs also significantly inhibited the neurotransmission in zebrafish. In addition, the PS-MPs exposure upregulated the expression of p53, gadd45ba, and casp3b resulting in apoptosis. We demonstrate that PS-MPs significantly upregulate the transcriptional pattern of tnfa and ptgs2a which are essential gene markers in inflammatory mechanism. Further, the oxidative damage induced by PS-MPs exposure could lead to cytological damage resulting in altered lamellar structures, capillary dilation, and necrosis in gill histomaps. In conclusion, the findings of this work strongly suggest that PS-MPs induce dose-and time-dependent ROS mediated apoptotic responses in zebrafish. Furthermore, the physiological responses observed in the gills correlate with the above observations and helps in unravelling the potential molecular mechanism underpinning the PS-MPs toxicity in zebrafish.

Immune response and susceptibility of Nile tilapia fish to Aeromonas hydrophila infection following the exposure to Bifenthrin and/or supplementation with Petroselinum crispum essential oil

Bifenthrin (BF) is a widely used 3rd generation type I pyrethroid with a potential toxic effect in fish. Nevertheless, its effect on the immune system remains unclear. In the present study, Oreochromis niloticus was exposed to BF at 0.68 μg/L for 60 days, followed by evaluating the hematological, biochemical, and immunological responses. Additionally, the potential of parsley (Petroselinum crispum) essential oil (PEO) to ameliorate the BF-induced toxic insults was explored. Our data have shown reductions in the growth performance with alterations observed in the hematological variables, protein profile and serum biomarkers of stress. DNA oxidative damage was evidenced by elevation of serum 8-hydroxy-2-deoxyguanosine (8-OHdG) content. BF-exposed fish presented also decline in serum lysozyme activity and levels of immunoglobulins (IgG and IgM) and nitric oxide (NO), with diminished resistance to Aeromonas hydrophila challenge. Furthermore, the RT-PCR analysis showed an upregulated expression pattern of immune -related genes including interleukin 1β (IL-1β), interferon - γ (IFN-γ) and tumor necrosis factor - α (TNF-α) genes in the liver tissue. Dietary co-supplementation of PEO at 1 or 2 mL/kg diet with concomitant BF exposure, alleviated the adverse effects of the insecticide in a dose-dependent manner. The observations from this study demonstrate the immunomodulation by BF and provide further insight into the protective properties of PEO and strengthen its applicability as a promising feed supplement to fish.

Effects of deltamethrin subacute exposure in snakehead fish, Channa argus: Biochemicals, antioxidants and immune responses

To evaluate the effects on biochemicals, antioxidants, immune responses and disease resistance of the snakehead fish, following exposure to deltamethrin at 0.061, 0.121, 0.242, 0.485 and 0.970 μg/L. After 28 d, the biochemical, the levels of antioxidant enzymes and immune enzymes in liver, spleen, kidney and intestine were negatively related to the concentrations of deltamethrin exposure. Likewise, the survival rates of the fish after 7 d challenge with Aeromonas veronii were negatively related. The levels of IL-1β, IL-8, TNF-α, Hsp70 and malondialdehyde in liver, spleen, kidney and intestine were positively connected to the concentrations of deltamethrin exposure. Results demonstrated that environmentally relevant concentrations (0.121, 0.242, 0.485 and 0.970 μg/L) inhibited the biochemicals, antioxidants and immune responses and disease resistance of snakehead fish.

Grass carps co-exposed to environmentally relevant concentrations of cypermethrin and sulfamethoxazole bear immunodeficiency and are vulnerable to subsequent Aeromonas hydrophila infection

The aquatic ecosystem is seriously damaged because of the heavy use of pesticides and antibiotics. Fish is the indispensable link between environmental pollution and human health. However, the toxic effects of environment-related concentrations of pesticides and antibiotics in fish have not been thoroughly studied. In this study, grass carps exposed to cypermethrin (CMN, 0.651 μg/L) or/and sulfamethoxazole (SMZ, 0.3 μg/L) for 42 days caused oxidative stress, apoptosis and immunodeficiency in the spleen of grass carps. CMN or/and SMZ exposure led to oxidative damage (consumption of antioxidant enzymes (superoxide dismutase and catalase)) and lipid peroxidation (accumulation of malondialdehyde), induced apoptosis (increases in TUNEL index, Bax/bcl-2, p53, puma and Caspase family expression). In addition, the levels of immunoglobulin M (IgM), complement 3 (C3) were significantly decreased in all treatment groups, which trend was also found in C-reactive protein in CMN and MIX group, and lysozyme in MIX group. Transcription of almost all genes involved in the Toll-like receptors (TLR) signaling pathway was up-regulated under CMN or/and SMZ exposure. However, when subsequently attacked by Aeromonas hydrophila for 2 days, the TLR pathway was inhibited in spleens of all treatment groups accompanied by higher mortality. Overall, the environmentally relevant concentration of CMN and SMZ damages the immune system, triggering oxidative stress and apoptosis in carps. And by affecting the conduction of TLR signaling pathway, CMN or/and SMZ exposure inhibits the innate immune response of fish and reducing their disease resistance. This study highlights the importance of rational and regulated use of these pesticides and antibiotics.