Effects of acute ammonia toxicity on oxidative stress, DNA damage and apoptosis in digestive gland and gill of Asian clam (Corbicula fluminea)

Harmful planktonic Microcystis and benthic Oscillatoria-induced toxicological effects on the Asian clam (Corbicula fluminea): A survey on histopathology, behavior, oxidative stress, apoptosis and inflammation

Cyanobacterial blooms are worldwide distributed and threaten aquatic ecosystems and public health. The current studies mainly focus on the adverse impacts of planktonic cyanobacteria or pure cyanotoxins, while the benthic cyanobacteria-induced ecotoxic effects are relatively lacking. The cyanobacterial cell-induced toxic effects on aquatic organisms might be more serious and complex than the pure cyanotoxins and crude extracts of cyanobacteria. This study explored the chronic effects of toxin-producing planktonic Microcystis aeruginosa (producing microcystin) and benthic Oscillatoria sp. (producing cylindrospermopsin) on the behaviors, tissue structures, oxidative stress, apoptosis, and inflammation of the Asian clams (Corbicula fluminea) under 28-d exposure. The data showed that both M. aeruginosa and Oscillatoria sp. can decrease the behaviors associated with the feeding activity and induce tissue damage (i.e. gill and digestive gland) in clams. Furthermore, two kinds of cyanobacteria can alter the antioxidant enzyme activities and increase antioxidant, lipid oxidation product, and neurotransmitter degrading enzyme levels in clams. Moreover, two kinds of cyanobacteria can activate apoptosis-related enzyme activities and enhance the proinflammatory cytokine levels of clams. In addition, two kinds of cyanobacteria can disturb the transcript levels of genes linked with oxidative stress, apoptosis, and inflammation. These results suggested harmful cyanobacteria can threaten the survival and health of clams, while the benthic cyanobacteria-induced adverse effects deserve more attention. Our finding also indicated that it is necessary to focus on the entire algal cell-induced ecotoxicity when concerning the ecological impacts of cyanobacterial blooms.

The effects of acute ammonia stress on liver antioxidant, immune and metabolic responses of juvenile yellowfin tuna (Thunnus albacares)

The impact of acute ammonia nitrogen (NH3-N) stress on the antioxidant, immune, and metabolic capabilities of the liver in juvenile yellowfin tuna (Thunnus albacares) is not yet fully understood. This study set NH3-N concentrations at 0 (natural seawater, control group), 5, and 10 mg/L, and sampled the liver at 6, 24, and 36 h for analysis. As time progresses, NH3-N exposure leads to an increase in malondialdehyde (MDA) concentrations. The activity of superoxide dismutase (SOD) and the relative expression levels of related genes, as well as the activity of immune enzymes and ATPase, decrease. The levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and interleukin-10 (IL-10) exhibit different fluctuation patterns. Low concentrations of NH3-N increase the activity of catalase (CAT) and glutathione peroxidase (GHS-PX) and the relative expression levels of the Na+K+-ATPase gene. The relative expression levels of the interleukin-6 receptor (IL-6r) gene show a decreasing trend. High concentrations of NH3-N decrease the activity of CAT, GSH-PX, and the relative expression levels of related genes. When the NH3-N concentration is below 5 mg/L, the stress duration should not exceed 36 h. When the NH3-N concentration is between 5 and 10 mg/L, the stress duration should not exceed 24 h, otherwise, it will have a negative impact on the liver of the juvenile yellowfin tuna. This study provides scientific data for the artificial breeding and recirculating aquaculture of juvenile yellowfin tuna.

Combined effects of toxic Microcystis aeruginosa and high pH on antioxidant responses, immune responses, and apoptosis of the edible freshwater bivalve Corbicula fluminea

Due to increasing anthropogenic perturbation and water eutrophication, cyanobacterial blooms (CYBs) have become a global ecological and environmental problem. Toxic CYBs and elevated pH are considered to be the two key stressors associated with eutrophication in natural waters, particularly in the event of CO2 depletion induced by dense blooms. However, previous research has been focused on investigating the impacts of toxic CYBs or pH changes in isolation, whereas the interactive effects of such stressors on edible bivalves that inhabit CYB waters still lack information. In this study, the combined effects of toxic Microcystis aeruginosa and pH shifts on the antioxidant responses, immune responses, and apoptosis of the edible freshwater bivalve Corbicula fluminea were explored. The results showed that the activity of antioxidant enzymes was significantly impacted by the interactive effects between toxic M. aeruginosa exposure and time course, yet pH shifts showed no significant effects on the activities of these antioxidant enzymes, implying that the antioxidant response in C. fluminea was mainly triggered by toxic M. aeruginosa exposure. Toxic M. aeruginosa also induced an increased production of reactive oxygen species and malondialdehyde in treated clams, particularly under high pH settings. The elevated lysosomal enzyme activity helped C. fluminea defend against toxic M. aeruginosa exposure under high pH conditions. The principal component analysis (PCA) and the integrated biomarker response (IBR) results suggested that the treated clams were subjected to the elevated toxicity of toxic M. aeruginosa in conditions of high pH. The heat shock proteins-related genes might be triggered to resist the oxidative damage in treated clams. Moreover, the upregulation of TNF and casp8 genes indicated the potential activation of the caspase8-mediated apoptotic pathway through TNF receptor interaction, potentially resulting in apoptosis. The TUNEL assay results further confirmed that apoptosis appeared in treated clams. These findings improve our understanding of the combined toxicological effects of harmful algae and pH shifts on bivalves, which will provide insights into a comprehensive ecological risk assessment of toxic CYBs to edible bivalve species.

The mechanism of reactive oxygen species generation, DNA damage and apoptosis in hemocytes of Litopenaeus vannamei under ammonia nitrogen exposure

Ammonia-N poses a significant threat to aquatic animals. However, the mechanism of ROS production leading to DNA damage in hemocytes of crustaceans is still unclear. Additionally, the mechanism that cells respond to DNA damage by activating complex signaling networks has not been well studied. Therefore, we exposed shrimp to 0, 2, 10, and 20 mg/L NH4Cl for 0, 3, 6, 12, 24, 48, and 72 h, and explored the alterations in endoplasmic reticulum stress and mitochondrial fission, DNA damage, repair, autophagy and apoptosis. The findings revealed that ammonia exposure led to an increase in plasma ammonia content and neurotransmitter content (DA, 5-HT, ACh), and significant changes in gene expression of PLC and Ca2+ levels. The expression of disulfide bond formation-related genes (PDI, ERO1) and mitochondrial fission-related genes (Drp1, FIS1) were significantly increased, and the unfolded protein response was initiated. Simultaneously, ammonia-N exposure leads to an increase in ROS levels in hemocytes, resulting in DNA damage. DNA repair and autophagy were considerably influenced by ammonia-N exposure, as evidenced by changes in DNA repair and autophagy-related genes in hemocytes. Subsequently, apoptosis was induced by ammonia-N exposure, and this activation was associated with a caspase-dependent pathway and caspase-independent pathway, ultimately leading to a decrease in total hemocytes count. Overall, we hypothesized that neurotransmitters in the plasma of shrimp after ammonia-N exposure bind to receptors on hemocytes membrane, causing endoplasmic reticulum stress through the PLC-IP3R-Ca2+ signaling pathway and leading to mitochondrial fission. Consequently, this process resulted in increased ROS levels, hindered DNA repair, suppressed autophagy, and activated apoptosis. These cascading effects ultimately led to a reduction in total hemocytes count. The present study provides a molecular support for the understanding of the detrimental toxicity of ammonia-N exposure to crustaceans.

Unraveling gene regulation mechanisms in fish: insights into multistress responses and mitigation through iron nanoparticles

The recent trend of global warming poses a significant threat to ecosystems worldwide. This global climate change has also impacted the pollution levels in aquatic ecosystems, subsequently affecting human health. To address these issues, an experiment was conducted to investigate the mitigating effects of iron nanoparticles (Fe-NPs) on arsenic and ammonia toxicity as well as high temperature stress (As+NH3+T). Fe-NPs were biologically synthesized using fish waste and incorporated into feed formulations at 10, 15, and 20 mg kg-1 diet. A total of 12 treatments were designed in triplicate following a completely randomized design involving 540 fish. Fe-NPs at 15 mg kg-1 diet notably reduced the cortisol levels in fish exposed to multiple stressors. The gene expressions of HSP 70, DNA damage-inducible protein (DDIP), and DNA damage were upregulated by stressors (As+NH3+T) and downregulated by Fe-NPs. Apoptotic genes (Cas 3a and 3b) and detoxifying genes (CYP 450), metallothionein (MT), and inducible nitric oxide synthase (iNOS) were downregulated by Fe-NPs at 15 mg kg-1 diet in fish subjected to As+NH3+T stress. Immune-related genes such as tumor necrosis factor (TNFα), immunoglobulin (Ig), and interleukin (IL) were upregulated by Fe-NPs, indicating enhanced immunity in fish under As+NH3+T stress. Conversely, Toll-like receptor (TLR) expression was notably downregulated by Fe-NPs at 15 mg kg-1 diet in fish under As+NH3+T stress. Immunological attributes such as nitro blue tetrazolium chloride, total protein, albumin, globulin, A:G ratio, and myeloperoxidase (MPO) were improved by dietary Fe-NPs at 15 mg kg-1 diet in fish, regardless of stressors. The antioxidant genes (CAT, SOD, and GPx) were also strengthened by Fe-NPs in fish. Genes associated with growth performance, such as growth hormone regulator (GHR1 and GHRβ), growth hormone (GH), and insulin-like growth factor (IGF 1X and IGF 2X), were upregulated, enhancing fish growth under stress, while SMT and MYST were downregulated by Fe-NPs in the diet. Various growth performance indicators were improved by dietary Fe-NPs at 15 mg kg-1 diet. Notably, Fe-NPs also enhanced arsenic detoxification and reduced the cumulative mortality after a bacterial infection. In conclusion, this study highlights that dietary Fe-NPs can effectively mitigate arsenic and ammonia toxicity as well as high temperature stress by modulating gene expression in fish.

The physiological response of oriental river prawn Macrobrachium nipponense to starvation-induced stress

Environmental stresses play critical roles in the physiology of crustaceans. Food deprivation is an important environmental factor and a regular occurrence in both natural aquatic habitats and artificial ponds. However, the underlying physiological response mechanisms to starvation-caused stress in crustaceans are yet to be established. In the present study, the hepatopancreas tissue of Macrobrachium nipponense was transcriptome analyzed and examined for starvation effects on oxidative stress, DNA damage, autophagy, and apoptosis across four fasting stages (0 (control group), 7, 14, and 21 days). These results indicated that a ROS-mediated regulatory mechanism is critical to the entire fasting process. At the initial stage of starvation (fasting 0 d ~ 7 d), ROS concentration increased gradually, activating antioxidant enzymes to protect the cellular machinery from the detrimental effects of oxidative stress triggered by starvation-induced stress. ROS content production (hydrogen peroxide and superoxide anion) then rose continuously with prolonged starvation (fasting 7 d ~ 14 d), reaching peak levels and resulting in autophagy in hepatopancreas cells. During the final stages of starvation (fasting 14 d ~ 21 d), excessive ROS induced DNA damage and cell apoptosis. Furthermore, autophagolysosomes and apoptosis body were further identified with transmission electron microscopy. These findings lay a foundation for further scrutiny of the molecular mechanisms combating starvation-generated stress in M. nipponense and provide fishermen with the theoretical guidance for adopting fasting strategies in M. nipponense aquaculture.

Adverse effects of Microcystis aeruginosa exudates on the filtration, digestion, and reproduction organs of benthic bivalve Corbicula fluminea

Cyanobacteria bloom and the secondary metabolites released by the microorganism are extremely harmful to aquatic animals, yet study on their adverse effects in zoobenthos is rare. Corbicula fluminea widely distributed in freshwater environment with algal blooms. It is a typical filter feeding zoobenthos that may be affected by the secondary metabolites of cyanobacteria due to its high filtering rate. In this study, C. fluminea was exposed to Microcystis aeruginosa exudates (MaE) for 96 h, which was obtained from 5 × 105 cells/mL and 2.5 × 106 cells/mL exponential stage M. aeruginosa culture solution that represented cyanobacteria cell density needs environmental risk precaution control and emergent control, respectively. The responses of C. fluminea critical organs to MaE were analyzed and evaluated based on histopathological sections, antitoxicity biomarkers, and organ function biomarkers. The results showed that all the organs underwent structural disorders, cell vacuolization, apoptosis, and necrosis, and the damage levels increased as MaE concentration increased. The detoxification and antioxidant defense systems biomarkers in each organ response to MaE exposure differently and the level of reaction improved when MaE concentration increased. The siphon rate and acetylcholinesterase activity showed that the filtration function decreased significantly as the MaE concentration increased. Increased activity of glutathione S-transferase and amylase in the digestive gland indicate that it is the major detoxification organ of C. fluminea. Increased vitellogenin concentration and enlarged oocytes in the gonad indicate that MaE may have an estrogenic effect on C. fluminea. This study demonstrates that cyanobacteria threat benthic bivalves by inducing oxidative stress, inhibiting filtering feeding system, and disturbing digestion system and reproduction potential of C. fluminea.

Response of antioxidation and immunity to combined influences of pH and ammonia nitrogen in the spotted babylon (Babylonia areolata)

Spotted babylon were exposed to three different pH levels (7.0, 8.0 and 9.0) and four different concentrations of ammonia nitrogen (0.02, 1.02, 5.10 and 10.20 mg/L) in seawater to determine their acute toxicity and physiological responses to environmental fluctuation. The study evaluated four antioxidant enzymes: catalase (CAT), alkaline, superoxide dismutase (SOD), peroxidase (POD) and glutathione peroxidase (GSH-PX), and two immunoenzymes: acid phosphatase (ACP) and phosphatase (AKP). Over time, the immunoenzyme activity was significantly affected by pH and ammonia nitrogen concentration. After being exposed to pH and ammonia nitrogen, the spotted babylon showed signs of unresponsiveness to external stimuli, reduced vitality, slow movement, and an inability to maintain an upright position. Over time, the spotted babylon exhibited a trend of increasing and then decreasing GSH-PX, CAT, and SOD activities to adapt to the changing environment and enhance its immunity. On the contrary, the POD and ACP activities exhibited a decreasing trend initially, followed by an increasing trend over time and the AKP activity showed a gradual increase with time. The combined effect of pH and ammonia was found to be stronger than the effect of either factor alone. The interaction between pH and ammonia increased the activity of the spotted babylon antioxidant enzymes, induced oxidative stress, and reduced the ability of the spotted babylon's non-specific immune system to reverse it. Thus, the reverse-back of the spotted babylon was higher when pH and ammonia stress were dual than when pH or ammonia were single-factor stresses. The study results will establish a theoretical basis for analyzing the risk of multiple factors to the spotted babylon, and also enrich the basic information about the shellfish immune system.

Impacts of acute ammonia-N exposure on the muscle quality of whiteleg shrimp (Penaeus vannamei): Novel insights into lipid and protein oxidation

This study explored the effect of ammonia-N exposure on the muscle quality of Penaeus vannamei and the underlying mechanisms based on the oxidation of lipids and proteins. Acute ammonia-N exposure reduced the hardness but increased the centrifugal loss and drip loss of the shrimp muscle. Meanwhile, reactive oxygen species and reactive nitrogen species were overproduced, thereby increasing the free fatty acid (FFA) content, fluorescent compound content, peroxide value (PV), and thiobarbituric acid reactive substance (TBAR) value. In addition, lipid peroxidation byproducts and free radicals could reduce sulfhydryl (SH) content and intrinsic fluorescence intensity. They may also increase carbonyl concentration, disulfide bond (SS) content, and surface hydrophobicity, and degrade myofibrillar protein, leading to the unfolding and conformational alterations in proteins in shrimp muscle. This study provided significant insights into the mechanisms underlying the impacts of ammonia toxicity on the quality of shrimp muscle.

The effect of astaxanthin on the alkalinity stress resistance of Exopalaemon carinicauda

Astaxanthin (Axn), a feed additive, can improve growth performance and enhance the environmental stress tolerance of shrimp at all growth stages. High carbonate alkalinity is considered a major stressor that affects the survival, growth, and reproduction of aquatic animals in saline-alkaline waters. In this study, a combined analysis of physiology, transcriptomics, and metabolomics was performed to explore the effected mechanism of Axn on Exopalaemon carinicauda (E. carinicauda) under alkalinity stress. The results revealed that dietary Axn can inhibit oxidative stress damage caused by alkalinity stress and maintain the normal cell structure and mitochondrial membrane potential. Transcriptomic data indicated that differentially expressed genes (DEGs) under alkalinity stress and those under alkalinity stress after Axn feeding were associated with apoptosis. The metabolic data suggested that alkalinity stress has adverse effects on ammonia metabolism, unsaturated fatty acid metabolism, and TCA cycle, and dietary Axn can improve the metabolic processes in E. carinicauda. In addition, transcriptomics and metabolomics analyses showed that Axn could help maintain the cytoskeletal structure and inhibit apoptosis under alkalinity stress; a TUNEL assay further confirmed these effects. Lastly, metabolic responses to alkalinity stress included changes in multiple amino acids and unsaturated fatty acids, and pathways related to energy metabolism were downregulated in the hepatopancreas of E. carinicauda under alkalinity stress. Collectively, all these results provide new insights into the molecular mechanisms underlying alkalinity stress tolerance in E. carinicauda after Axn feeding.

Toxic effects of combined exposure to homoyessotoxin and nitrite on the survival, antioxidative responses, and apoptosis of the abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) and nitrite (NO2-N), released during harmful dinoflagellate cell lysis adversely affect abalones. However, their toxicity mechanisms in shellfish remain unclear. This study investigated the economic abalone species Haliotis discus hannai exposed to varying concentrations of homo-YTX (0, 2, 5, and 10 µg L-1) and NO2-N (0, 3, and 6 mg L-1) on the basis of their 12 h LC50 values (5.05 µg L-1 and 4.25 mg L-1, respectively) and the environmentally relevant dissolved concentrations during severe dinoflagellate blooms, including mixtures. The test abalones were exposed to homo-YTX and NO2-N for 12 h. The mortality rate (D), reactive oxygen species (ROS) levels, antioxidant defense capabilities, and expression levels of antioxidant-related, Hsp-related, and apoptosis-related genes in abalone gills were assessed. Results showed that the combined exposure to homo-YTX and NO2-N increased the D and ROS levels and upregulated B-cell lymphoma-2 (BCL2)-associated X (BAX) and caspase3 (CASP3) expression levels while reducing glutathione peroxidase (GPx) activity and GPx, CuZnSOD, and BCL2 expression levels. High concentrations of homo-YTX (10 µg L-1) and NO2-N (6 mg L-1) solutions and the combinations of these toxicants inhibited the activities of superoxide dismutase (SOD) and catalase (CAT) and downregulated the expression levels of MnSOD, CAT, Hsp70, and Hsp90. The ROS levels were negatively correlated with the activities of SOD, CAT, and GPx and the expression levels of MnSOD, CuZnSOD, CAT, GPx, Hsp70, Hsp90, and BCL2. These results suggest that homo-YTX, in conjunction with NO2-N, induces oxidative stress, disrupts antioxidant defense systems, and triggers caspase-dependent apoptosis in the gills of abalone. ROS-mediated antioxidative and heat-shock responses and apoptosis emerge as potential toxicity mechanisms affecting the survival of H. discus hannai due to homo-YTX and NO2-N exposure.

Ammonia-induced oxidative stress triggered apoptosis in the razor clam (Sinonovacula constricta)

As one of the most significant contaminants and stressors in aquaculture systems, ammonia adversely jeopardizes the health of aquatic animals. Ammonia exposure affects the development, metabolism, and survival of shellfish. However, the responses of the innate immune and antioxidant systems and apoptosis in shellfish under ammonia stress have rarely been reported. In this study, razor clams (Sinonovacula constricta) were exposed to different concentrations of non-ion ammonia (0.25 mg/L, 2.5 mg/L) for 72 h and then placed in ammonia-free seawater for 72 h for recovery. The immune responses induced by ammonia stress on razor clams were investigated by antioxidant enzyme activities and degree of apoptosis in digestive gland and gill tissues at different time points. The results showed that exposure to a high concentration of ammonia greatly disrupted the antioxidant system of the razor clam by exacerbating the accumulation of reactive oxygen species ( O 2 - , H2O2) and disordering the activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and the level of activity remained at a significantly high level after recovering for 72 h (P < 0.05). In addition, there were significant differences (P < 0.05) in the expression of key genes (Caspase 7, Cyt-c, Bcl-2, and Bax) in the mitochondrial apoptotic pathway in the digestive glands and gills of razor clams as a result of ammonia stress and were unable to return to normal levels after 72 h of recovery. TUNEL staining indicated that apoptosis was more pronounced in gills, showing a dose and time-dependent pattern. As to the results, ammonia exposure leads to the activation of innate immunity in razor clams, disrupts the antioxidant system, and activates the mitochondrial pathway of apoptosis. This is important for comprehending the mechanism underlying the aquatic toxicity resulting from ammonia in shellfish.

Effects of Ocimum basilicum essential oil and ginger extract on serum biochemistry, oxidative stress and gill tissue damage of pearl gentian grouper during simulated live transport

This study explored the effects of the essential oil of Ocimum basilicum (EOOB) and ginger extract (GE) during the transportation of pearl gentian grouper from water quality, serum biochemistry, oxidative stress, meat flavor, and gill tissue morphology. Fish (450 ± 50 g) were allocated to the following 5 treatments: control group (fish transported in water only), 5 mg/LEOOB, 10 mg/LEOOB, 3 mg/LGE, and 6 mg/LGE and transported in insulation boxes (66 × 51 × 37.8 cm) for 72 h. Samples were taken at 0, 12, 36, 60, and 72 h immediately after transport. It was found that 10 mg/LEOOB and 6 mg/LGE could reduce the levels of total ammonia nitrogen (TAN), dissolved oxygen (DO), water pH, serum glucose (GLU), cortisol (COR), liver superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GPX), increase the activities of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH), as well as significantly increase the total free amino acid (TFAA) content in muscle compared to the control group (P < 0.05). In addition, by observing the microstructure of gill tissue, it was found that compared with untreated grouper, the morphological damage of gill tissue in EOOB and GE treatment was alleviated. These results indicated that adding appropriate amounts of EOOB and GE to transport water could improve the water quality, relieve stress, and lower energy metabolism of grouper during transport. The results of this research will help to improve the survival rate of grouper after transportation and decrease economic losses to fishery.

Integrated analysis of physiological, transcriptome, and metabolome analyses of the gills in Solenaia oleivora under ammonia exposure

Ammonia is a common toxicant in aquatic systems and one of the key factors affecting aquaculture. However, data on mollusks' toxic response and coping mechanisms to ammonia nitrogen, especially freshwater mollusks, are still lacking. In this study, we evaluated the tolerance of a freshwater mollusk Solenaia oleivora to ammonia and investigated its coping mechanisms by combining physiological, metabolic, and transcriptomic analyses in the gills. The acute toxicity test revealed that the LC50-96 h (temperature-20 ℃, pH-7.4) of ammonia in S. oleivora was 63.29 mg/L. The physiological and TUNEL results showed that although 10 mg/L ammonia exposure increased the activities of antioxidant, immune and ammonia detoxification-related enzymes, it still caused oxidative damage and cell apoptosis of gill tissues. A total of 97 differential metabolites (DMs) and 3431 differential expressed genes (DEGs) were identified after ammonia stress. Among them, most DMs and DEGs were involved in immune response, antioxidant, cell apoptosis, carbohydrate metabolism, amino acid metabolism, and lipid metabolism. The enhancement of glycolysis and lipid metabolisms may provide energy for immune response and ammonia detoxification. In addition, glutamine synthesis, alanine synthesis and urea cycle were involved in ammonia nitrogen detoxification in the gill tissue of S. oleivora. Our results indicate that ammonia leads to individual death in S. oleivora, as wells as oxidative damage, cell apoptosis, immune response, and metabolic changes of gill tissues. The findings will provide valuable information to assess the potential ecological risk of environmental ammonia to freshwater mollusks and theoretical guidance for the healthy aquaculture of S. oleivora.

Understanding the molecular mechanism of arsenic and ammonia toxicity and high-temperature stress in Pangasianodon hypophthalmus

The current investigation explores the mechanisms of ammonia and arsenic toxicity, along with high-temperature stress, which other researchers rarely addressed. Pangasianodon hypophthalmus was exposed to low doses of ammonia and arsenic (1/10th of LC50, 2.0 and 2.68 mg L-1, respectively) and high temperature (34 °C) for 105 days. The following treatments were applied: control (unexposed), arsenic (As), ammonia (NH3), ammonia + arsenic (NH3 + As), ammonia + temperature (NH3 + T), and NH3 + As + T. Cortisol levels significantly increased with exposure to ammonia (NH3), arsenic (As), and high temperature (34 °C) compared to the unexposed group. Heat shock protein (HSP 70), inducible nitric oxide synthase (iNOS), and metallothionein (MT) gene expressions were notably upregulated by 122-210%, 98-122%, and 64-238%, respectively, compared to the control. Neurotransmitter enzymes (acetylcholine esterase, AChE) were significantly inhibited by NH3 + As + T, followed by other stressor groups. The apoptotic (caspase, Cas 3a and 3b) and detoxifying (cytochrome P450, CYP P450) pathways were substantially affected by the NH3 + As + T group. Immune (total immunoglobulin, Ig; tumor necrosis factor TNFα; and interleukin IL) and growth-related genes (growth hormone, GH; growth hormone regulator, GHR1 and GHRβ; myostatin, MYST and somatostatin, SMT) were noticeably upregulated by NH3 + As + T, followed by other stress groups, compared to the control group. Weight gain %, protein efficiency ratio, feed efficiency ratio, specific growth rate, and other growth attributes were significantly affected by low doses of ammonia, arsenic, and high-temperature stress. Albumin, total protein, globulin, A:G ratio, and myeloperoxidase (MPO) were highly affected by the As + NH3 + T group. Blood profiling, including red blood cells (RBC), white blood count (WBC), and hemoglobin (Hb), were also impacted by stressor groups compared to the control group. Genotoxicity, as DNA damage, was significantly higher in groups exposed to NH3 + As + T (89%), NH3 + T (78%), NH3 (73), NH3 + As (71), and As (68%). The bioaccumulation of arsenic was substantially higher in liver and kidney tissues. The present study contributes to understanding the toxicity mechanisms of ammonia and arsenic, as well as high-temperature stress, through different gene expressions, biochemical attributes, genotoxicity, immunological status, and growth performance of P. hypophthalmus.

Anthropogenic underwater noise: A review on physiological and molecular responses of marine biota

The detrimental effects of anthropogenic underwater noise on marine organisms have garnered significant attention among scientists. This review delves into the research concerning the repercussions of underwater noise on marine species, with specific emphasis on the physiological and molecular responses of marine biota. This review investigates the sensory mechanisms, hearing sensitivity, and reaction thresholds of diverse marine organisms, shedding light on their susceptibility to underwater noise disturbances. The physiological and molecular effects of anthropogenic underwater noise on marine biota include oxidative stress, energy homeostasis, metabolism, immune function, and respiration. Additionally, changes in the gene expression profile associated with oxidative stress, metabolism, and immunological response are among the responses reported for marine biota. These effects pose a threat to animal fitness and potentially affect their survival as individuals and populations.

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.

Mechanisms of ammonotelism, epithelium damage, cellular apoptosis, and proliferation in gill of Litopenaeus vannamei under NH4Cl exposure

Excessive ammonia-N in coastal environment and aquaculture threatens the health of marine organisms. To explore the mechanism of gill damage induced by ammonia-N, transcriptome of Litopenaeus vannamei 's gill was carried out under 20 mg/L NH4Cl for 0, 6, and 48 h. K-means clustering analysis suggested that ammonia excretion and metabolism-related genes were elevated. GO and KEGG enrichment analysis suggested that glycosyltransferase activity and amino acid metabolism were affected by ammonia. Moreover, histological observation via three staining methods gave clues on the changes of gill after ammonia-N exposure. Increased mucus, hemocyte infiltration, and lifting of the lamellar epithelium suggested that gill epithelium was suffering damage under ammonia-N stress. Meanwhile, the composition of extracellular matrix (ECM) in connective tissue changed. Based on the findings of transcriptomic and histological analysis, we further investigated the molecular mechanism of gill damage under multiple concentrations of NH4Cl (0, 2, 10, 20 mg/L) for multiple timepoints (0, 3, 6, 12, 24, 48, 72 h). First, ammonia excretion was elevated via ion channel, transporter, and exocytosis pathways, but hemolymph ammonia still kept at a high level under 20 mg/L NH4Cl exposure. Second, we focused on glycosaminoglycan metabolism which was related to the dynamics of ECM. It turned out that the degradation and biosynthesis of chondroitin sulfate (CS) were elevated, suggesting that the structure of CS might be destructed under ammonia-N stress and CS played an important role in maintaining gill structure. It was enlightening that the destructions occurred in extracellular regions were vital to gill damage. Third, ammonia-N stress induced a series of cellular responses including enhanced apoptosis, active inflammation, and inhibited proliferation which were closely linked and jointly led to the impairment of gill. Our results provided some insights into the physiological changes induced by ammonia-N and enriched the understandings of gill damage under environmental stress.

ROS-mediated physiological activities and apoptotic effect on the survival of abalone (Haliotis discus hannai) under homoyessotoxin and ammonia stresses

Serious dinoflagellate blooms produce homoyessotoxin (homo-YTX) and ammonia (NH3-N) in eutrophic seawaters, posing threats to the healthy development of the mariculture industry. This study aimed to explore the toxicity mechanism of homo-YTX and NH3-N on the survival of abalone, which is important for the ecotoxicological research and cultivation of shellfish. The economy abalone Haliotis discus hannai was placed in homo-YTX (0, 2, 5, and 10 μg L-1) and NH3-N (0, 1.08, and 3.16 mg L-1) and a mixture of the two compounds to determine the survival rate (S), antioxidative responses, physiological activities, and apoptosis of abalone. Results show that the combination of homo-YTX and NH3-N increased the reactive oxygen species level, the malondialdehyde content, and the expression level of BCL2-associated X but decreased S; the activities of superoxide dismutase, catalase, adenosine triphosphatase, glutamic-pyruvic transaminase, xanthine oxidase, lactate dehydrogenase, and lysozyme; and the expression level of B-cell lymphoma-2. The activities of alkaline phosphatase and acid phosphatase in 10 μg L-1 of homo-YTX and 3.16 mg L-1 of NH3-N solutions and in the mixture of the two toxicants decreased. The caspase3 expression level was downregulated in 10 μg L-1 of homo-YTX. These results suggest that homo-YTX and NH3-N enhanced the oxidative stress and lipid peroxidation reactions, inhibited the energy supply, disrupted the metabolic and immune physiological functions, and activated apoptosis in the gills of abalone. ROS-mediated physiological activities and apoptosis were among the potential toxicity mechanisms of the interactive effects of homo-YTX and NH3-N on abalone.

BDE-209-induced genotoxicity, intestinal damage and intestinal microbiota dysbiosis in zebrafish (Danio Rerio)

The environmental presence of polybrominated diphenyl ethers (PBDEs) is ubiquitous due to their wide use as brominated flame retardants in industrial products. As a common congener of PBDEs, decabromodiphenyl ether (BDE-209) can pose a health risk to animals as well as humans. However, to date, few studies have explored BDE-209's toxic effects on the intestinal tract, and its relevant mechanism of toxicity has not been elucidated. In this study, adult male zebrafish were exposed to BDE-209 at 6 μg/L, 60 μg/L and 600 μg/L for 28 days, and intestinal tissue and microbial samples were collected for analysis to reveal the underlying toxic mechanisms. Transcriptome sequencing results demonstrated a dose-dependent pattern of substantial gene differential expression in the group exposed to BDE-209, and the differentially expressed genes were mainly concentrated in pathways related to protein synthesis and processing, redox reaction, and steroid and lipid metabolism. In addition, BDE-209 exposure caused damage to intestinal structure and barrier function, and promoted intestinal oxidative stress, inflammatory response, apoptosis and steroid and lipid metabolism disorders. Mechanistically, BDE-209 induced intestinal inflammation by increasing the levels of TNF-α and IL-1β and activating the NFκB signaling pathway, and might induce apoptosis through the p53-Bax/Bcl2-Caspase3 pathway. BDE-209 also significantly inhibited the gene expression of rate-limiting enzymes such as Sqle and 3βhsd (p < 0.05) to inhibit cholesterol synthesis. In addition, BDE-209 induced lipid metabolism disorders through the mTOR/PPARγ/RXRα pathway. 16S rRNA sequencing results showed that BDE-209 stress reduced the richness and diversity of intestinal microbiota, and reduced the abundance of probiotics (e.g., Bifidobacterium and Faecalibacterium). Overall, the results of this study help to clarify the intestinal response mechanism of BDE-209 exposure, and provide a basis for evaluating the health risks of BDE-209 in animals.

microRNA-mRNA Analysis Reveals Tissue-Specific Regulation of microRNA in Mangrove Clam (Geloina erosa)

Geloina erosa is an important benthic animal in the mangrove, serving as an indicator organism for coastal environmental pollution. This study aimed to investigate the tissue-specific expression of miRNAs and their regulatory roles in predicted targets in G. erosa. Through miRNA sequencing and co-expression network analysis, we extensively studied the miRNA expression in three tissues: gills, hepatopancreas, and muscle. The results revealed a total of 1412 miRNAs, comprising 1047 known miRNAs, and 365 newly predicted miRNAs. These miRNAs exhibited distinct tissue-specific expression patterns. In the miRNA target gene prediction, a total of 7404 potential predicted targets were identified, representing approximately 33% of all unique transcripts associated with miRNAs. Further co-expression network analysis revealed nine modules, each showing a positive correlation with specific tissues (gills, hepatopancreas, or muscle). The blue module showed a significant correlation with gills (r = 0.83, p-value = 0.006), the black module was significantly related to the hepatopancreas (r = 0.78, p-value = 0.01), and the purple module was significantly correlated with muscle (r = 0.83, p-value = 0.006). Within these modules, related miRNAs tended to cluster together, while their correlations with other modules were relatively weak. Functional enrichment analysis was performed on miRNAs and their predicted targets in each tissue. In the gills, miRNAs primarily regulate immune-related genes, substance transport, and cytoskeletal organization. In the hepatopancreas, miRNAs suppressed genes involved in shell formation and played a role in cellular motor activity and metabolism. In muscle, miRNAs participate in metabolism and photoreceptive processes, as well as immune regulation. In summary, this study provides valuable insights into the tissue-specific regulation of miRNAs in G. erosa, highlighting their potential roles in immune response, metabolism, and environmental adaptation. These findings offer important clues for understanding the molecular mechanisms and biological processes in G. erosa, laying the foundation for further validation and elucidation of these regulatory relationships.

Differential Toxicity Responses between Hepatopancreas and Gills in Litopenaeus vannamei under Chronic Ammonia-N Exposure

Ammonia nitrogen is one of the main toxic substances in aquatic cultivation environments. Chronic exposure to excessive amounts of ammonia-N creates toxic consequences, retarding the growth of aquatic organisms. This study investigated the growth performance, morphological and physiological alterations, and transcriptome changes in the hepatopancreas and gills of white shrimp Litopenaeus vannamei. The results showed that there was no significant difference in the survival rate (p > 0.05), whereas growth performance was reduced significantly in the treated groups compared to the control groups (p < 0.05). Significant structural damage and vacuolation occurred in hepatopancreas and gill tissues in the treated groups. Superoxide dismutase (SOD) activity and Na+/K+-ATPase content were significantly increased by chronic ammonia-N exposure in the two tissue groups. In addition, catalase (CAT) activity and malondialdehyde (MDA) levels were significantly altered in the hepatopancreas groups (p < 0.05), whereas no differences were observed in the gill groups (p > 0.05). There were 890 and 1572 differentially expressed genes identified in the hepatopancreas (treated versus control groups) and gills (treated versus control groups), respectively, of L. vannamei under chronic ammonia-N exposure. Functional enrichment analysis revealed associations with oxidative stress, protein synthesis, lipid metabolism, and different serine proteases. The gills maintained cellular homeostasis mainly through high expression of cytoskeleton and transcription genes, whereas the hepatopancreas down-regulated related genes in the ribosome, proteasome, and spliceosome pathways. These genes and pathways are important in the biosynthesis and transformation of living organisms. In addition, both tissues maintained organismal growth primarily through lipid metabolism, which may serve as an effective strategy for ammonia-N resistance in L. vannamei. These results provided a new perspective in understanding the mechanisms of ammonia-N resistance in crustaceans.

Transcriptomic analysis revealed the dynamic response mechanism to acute ammonia exposure in the ivory shell, Babylonia areolata

The ivory shell (Babylonia areolata) is an economically important shellfish in tropical and subtropical regions, but its intensive culture and biological characteristic of hiding in the sandy substrate make it highly susceptible to ammonia stress. In this study, we investigated the dynamic changes in histopathology, oxidative stress, and transcriptome of the ivory shell at different time points under high concentration (60 mg/L) ammonia exposure. With prolonged exposure to stress, vacuoles appeared in the hepatopancreas while cell volume and intercellular space increased. The activities of superoxide dismutase (SOD) and catalase (CAT) decreased significantly under high concentrations of ammonia-induced stress while malondialdehyde (MDA) levels increased significantly. Integrated analysis of differentially expressed genes (DEGs), weighted gene co-expression network analysis (WGCNA), and quantitative real-time polymerase chain reaction (qRT-PCR) revealed that lipid transport primarily contributed to maintaining cellular homeostasis during the early stage of stress (6 and 12 h). Subsequently, a significant upregulation of oxidation-reduction reactions occurred at the middle stage (24 h), leading to oxidative stress. Finally, during the later stage (48 h), metabolic decomposition provided energy for survival maintenance. Additionally, lysosome and apoptosis were identified as potential key pathways in response to acute ammonia toxicity. Overall, our findings suggest that ivory shells can respond to acute ammonia toxicity via immune and antioxidant defense mechanisms but sustained high concentrations may cause irreversible damage. This study provides valuable insights into the response mechanism of mollusks towards ammonia and serves as a data reference for breeding ammonia-tolerant varieties of ivory shells.

α-lipoic acid ameliorates hepatotoxicity induced by chronic ammonia toxicity in crucian carp (Carassius auratus gibelio) by alleviating oxidative stress, inflammation and inhibiting ERS pathway

High environment ammonia (HEA) poses a deadly threat to aquatic animals and indirectly impacts human healthy life, while nutritional regulation can alleviate chronic ammonia toxicity. α-lipoic acid exhibits antioxidative effects in both aqueous and lipid environments, mitigating cellular and tissue damage caused by oxidative stress by aiding in the neutralization of free radicals (reactive oxygen species). Hence, investigating its potential as an effective antioxidant and its protective mechanisms against chronic ammonia stress in crucian carp is highly valuable. Experimental fish (initial weight 20.47 ± 1.68 g) were fed diets supplemented with or without 0.1% α-lipoic acid followed by a chronic ammonia exposure (10 mg/L) for 42 days. The results revealed that chronic ammonia stress affected growth (weight gain rate, specific growth rate, and feed conversion rate), leading to oxidative stress (decreased the activities of antioxidant enzymes catalase, superoxide dismutase, glutathione peroxidase; decreased total antioxidant capacity), increased lipid peroxidation (accumulation of malondialdehyde), immune suppression (decreased contents of nonspecific immune enzymes AKP and ACP, 50% hemolytic complement, and decrease of immunoglobulin M), impaired ammonia metabolism (reduced contents of Glu, GS, GSH, and Gln), imbalance of expression of induced antioxidant-related genes (downregulation of Cu/Zu SOD, CAT, Nrf2, and HO-1; upregulation of GST and Keap1), induction of pro-apoptotic molecules (transcription of BAX, Caspase3, and Caspase9), downregulation of anti-apoptotic gene Bcl-2 expression, and induction of endoplasmic reticulum stress (upregulation of IRE1, PERK, and ATF6 expression). The results suggested that the supplementation of α-lipoic acid could effectively induce humoral immunity, alleviate oxidative stress injury and endoplasmic reticulum stress, and ultimately alleviate liver injury induced by ammonia poisoning (50-60% reduction). This provides theoretical basis for revealing the toxicity of long-term ammonia stress and provides new insights into the anti-ammonia toxicity mechanism of α-lipoic acid.

A review of the toxic effects of ammonia on invertebrates in aquatic environments

Aquatic invertebrates are the organisms most susceptible to ammonia toxicity. However, the toxic effects of ammonia on invertebrates are still poorly understood. This study reviews the research progress in ammonia toxicology for the period from 1986 to 2023, focusing on the effects on invertebrates. Through examining the toxic effects of ammonia at different levels of organization (community, individual, tissue and physiology, and molecular) as well as the results from omics studies, we determined that the most significant effects were on the reproductive capacity of invertebrates and the growth of offspring, although different populations show variation in their tolerance to ammonia, and tissues have varied potential to respond to ammonia stress. A multicomponent analysis is an in-depth technique employed in toxicological studies, as it can be used to explore the enrichment pathways and functional genes expressed under ammonia stress. This study comprehensively discusses ammonia toxicity from multiple aspects in order to provide new insights into the toxic effects of ammonia on aquatic invertebrates.

Ammonia nitrogen stress damages the intestinal mucosal barrier of yellow catfish (Pelteobagrus fulvidraco) and induces intestinal inflammation

Nitrogen from ammonia is one of the most common pollutants toxics to aquatic species in aquatic environment. The intestinal mucosa is one of the key mucosal defenses of aquatic species, and the accumulation of ammonia nitrogen in water environment will cause irreversible damage to intestinal function. In this study, histology, immunohistochemistry, ultrastructural pathology, enzyme activity analysis and qRT-PCR were performed to reveal the toxic effect of ammonia nitrogen stress on the intestine of Pelteobagrus fulvidraco. According to histological findings, ammonia nitrogen stress caused structural damage to the intestine and reduced the number of mucous cells. Enzyme activity analysis revealed that the activity of bactericidal substances (Lysozyme, alkaline phosphatase, and ACP) had decreased. The ultrastructure revealed sparse and shortened microvilli as well as badly degraded tight junctions. Immunohistochemistry for ZO-1 demonstrated an impaired intestinal mucosal barrier. Furthermore, qRT-PCR revealed that tight junction related genes (ZO-1, Occludin, Claudin-1) were downregulated, while the pore-forming protein Claudin-2 was upregulated. Furthermore, as ammonia nitrogen concentration grew, so did the positive signal of Zap-70 (T/NK cell) and the expression of inflammation-related genes (TNF, IL-1β, IL-8, IL-10). In light of the above findings, we conclude that ammonia nitrogen stress damages intestinal mucosal barrier of Pelteobagrus fulvidraco and induces intestinal inflammation.

First transcriptome profiling in gill and hepatopancrease tissues of Metapenaeus ensis in response to acute ammonia-N stress

The greasyback shrimp, Metapenaeus ensis, suffers from ammonia-N stress during intensive factory aquaculture. Optimizing ammonia-N stress tolerance has become an important issue in M. ensis breeding. The metabolic and adaptive mechanisms of ammonia-N toxicity in M. ensis have not been comprehensively understood yet. In this study, a large number of potential simple sequence repeats (SSRs) in the transcriptome of M. ensis were identified. Differentially expressed genes (DEGs) in the gill and hepatopancreas at 24 h post-challenges under high concentrations of ammonia-N treatment were detected. We obtained 20,108,851-27,681,918 clean reads from the control and high groups, assembled and clustered a total of 103,174 unigenes with an average of 876 bp and an N50 of 1189 bp. Comparative transcriptome analyses identified 2000 different expressed genes in the gill and 2010 different expressed genes in the hepatopancreas, a large number of which were related to immune function, oxidative stress, metabolic regulation, and apoptosis. The results suggest that M. ensis may counteract ammonia-N toxicity at the transcriptome level by increasing the expression of genes related to immune stress and detoxification metabolism, and that selected genes may serve as molecular indicators of ammonia-N. By exploring the genetic basis of M. ensis' ammonia-N stress adaptation, we constructed the genetic networks for ammonia-N adaptation. These findings will accelerate the understanding of M. ensis' ammonia-N adaptation, contribute to the research of future breeding, and promote the level of factory aquaculture of M. ensis.

Toxicological mechanism of ammonia-N on haematopoiesis and apoptosis of haemocytes in Litopenaeus vannamei

Ammonia, as an important pollutant, contributed to the reduction of immunity, disruption of physiology in animals. RNA interference (RNAi) was performed to understand the function of astakine (AST) in haematopoiesis and apoptosis in Litopenaeus vannamei under ammonia-N exposure. Shrimps were exposed to 20 mg/L ammonia-N from 0 to 48 h with injection of 20 μg AST dsRNA. Further, shrimps were exposed to 0, 2, 10 and 20 mg/L ammonia-N also from 0 to 48 h. The results showed that the total haemocytes count (THC) decreased under ammonia-N stress and the knockdown of AST resulted in a further decrease of THC, suggesting that 1) the proliferation was decreased through the reduction of AST and Hedgehog, the differentiation was interfered by Wnt4, Wnt5 and Notch, and the migration was inhibited by the decrease of VEGF; 2) oxidative stress was induced under ammonia-N stress, leading to the increase of DNA damage with the up-regulated gene expression of death receptor, mitochondrial and endoplasmic reticulum stress pathways; 3) the changes of THC resulted from the decrease of proliferation, differentiation and migration of haematopoiesis cells and the increase of apoptosis of haemocytes. This study helps to deepen our understanding of risk management in shrimp aquaculture.

High dissolved oxygen exacerbates ammonia toxicity with sex-dependent manner in zebrafish

Ammonia nitrogen is one of the important environmental factors, and causes negative effects for fish health in ecosystem and aquaculture. The toxic effects and mechanisms of ammonia in fish deserve further investigation. In the present study, we exposed female and male zebrafish (Danio rerio) to ammonia (50 mg/L NH₄Cl) with oxygenated (7.5-7.8 mg/L) or non‑oxygenated (3.8-4.5 mg/L) water, to identify the combined effects of dissolved oxygen and ammonia on fish with gender difference. The results showed that oxygenated ammonia exposure increased fish mortality, gill secondary lamellas damage and gill tissue spaces, gene expressions of proinflammatory interleukin 1 beta (il-1β) and apoptotic caspase8 as compared with non‑oxygenated ammonia. Besides, oxygenated ammonia elevated plasma ammonia contents, and decreased the discharge of body ammonia through gills by depressing the enzyme activity of Na⁺/K⁺-ATPase. Notably, when zebrafish were subjected to ammonia stress, more severe mortality, gill damage and tissue inflammatory response were observed in males than females. This is the first study to clarify the gender-dependent impacts of ammonia toxicity, and the adverse effects of oxygenation on ammonia resistance in zebrafish.

Ammonia Toxicity in the Bighead Carp (Aristichthys nobilis): Hematology, Antioxidation, Immunity, Inflammation and Stress

Ammonia is one of the main environmental pollutants that affect the survival and growth of fish. The toxic effects on blood biochemistry, oxidative stress, immunity, and stress response of bighead carp (Aristichthys nobilis) under ammonia exposure were studied. Bighead carp were exposed to total ammonia nitrogen (TAN) concentrations of 0 mg/L, 3.955 mg/L, 7.91 mg/L, 11.865 mg/L, and 15.82 mg/L for 96 h. The results showed that ammonia exposure significantly reduced hemoglobin, hematocrit, red blood cell, white blood cell count, and platelet count and significantly increased the plasma calcium level of carp. Serum total protein, albumin, glucose, aspartate aminotransferase, and alanine aminotransferase changed significantly after ammonia exposure. Ammonia exposure can induce intracellular reactive oxygen species (ROS), and the gene expression of antioxidant enzymes (Mn-SOD, CAT, and GPx) increases at the initial stage of ammonia exposure, while MDA accumulates and antioxidant enzyme activity decreases after ammonia stress. Ammonia poisoning changes the gene expression of inflammatory cytokines; promotes the gene expression of inflammatory cytokines TNF-α, IL-6, IL-12, and IL-1β; and inhibits IL-10. Furthermore, ammonia exposure led to increases in stress indexes such as cortisol, blood glucose, adrenaline, and T3, and increases in heat shock protein 70 and heat shock protein 90 content and gene expression. Ammonia exposure caused oxidative stress, immunosuppression, inflammation, and a stress reaction in bighead carp.

In Vitro Anticancer Activity of Novel Ciprofloxacin Mannich Base in Lung Adenocarcinoma and High-Grade Serous Ovarian Cancer Cell Lines via Attenuating MAPK Signaling Pathway

Novel drugs are desperately needed in order to combat a significant challenge due to chemo-therapeutic resistance and bad prognosis. This research aimed to assess the anticancer activity of a newly synthesized ciprofloxacin Mannich base (CMB) on ovarian cancer (OVCAR-3) and lung cancer (A-549) cell lines and to investigate probable involved molecular mechanisms. The cytotoxic and pro-apoptotic impact of CMB on both cell lines was investigated using MTT assay, Annexin V assay, and cell cycle analysis, as well as caspase-3 activation. Western blotting was carried out to evaluate downstream targets of the MAPK pathway, while qRT PCR was used to evaluate the gene expression pattern of the p53/Bax/Bcl2 pathway. CMB treatment showed significantly reduced cell proliferation in both OVCAR-3 and A-549 cells with half maximum inhibitory concentration (IC₅₀) = 11.60 and 16.22 µg/mL, respectively. CMB also induced apoptosis, S phase cell cycle arrest, and up-regulated expression of p53, p21, and Bax while down-regulated Bcl2 expression. CMB also halted cell proliferation by deactivating the MAPK pathway. In conclusion, CMB may be regarded as a potential antiproliferative agent for lung and ovarian cancers due to anti-proliferative and pro-apoptotic actions via inhibition of the MAPK pathway and p53/Bax/Bcl2.

Benzotriazole UV stabilizer-induced genotoxicity in freshwater benthic clams: A survey on apoptosis, oxidative stress, histopathology and transcriptomics

Benzotriazole UV stabilizer-329 (UV-329) is frequently detected in various environmental and biological matrices. However, the toxicity effect on freshwater benthos induced by UV-329 has rarely been described. In this study, genotoxicity, apoptosis, oxidative stress, histopathological alterations, siphoning behavior, and bioaccumulation in the gill and digestive gland of Corbicula fluminea exposed to UV-329 at 10, 100, and 1000 μg/L for 21 days were investigated. Toxicity screening using transcriptomics confirmed that UV-329 preferentially stimulated cellular process-related pathways including gap junctions, apoptosis, phagosomes and necroptosis. The transcript levels of a large number of apoptosis genes were significantly upregulated. This apoptosis mechanism was further confirmed by the fact that UV-329 exposure significantly increased the percentage of apoptotic cells, activated caspase-3, -8, and -9, and affected the antioxidant enzyme activities. Following exposure to 1000 μg/L UV-329, significant histological alterations were reflected in the corrosion of cilia, cellular swelling of epithelial cells in the gills, degeneration of digestive tubules, and necrosis of epithelial cells in the digestive glands. These results may aid in elucidating the toxicity mechanism of UV329 in bivalves and evaluating the hazards of UV-329 in benthic ecosystems.

Effect of sub-lethal ammonia and nitrite stress on autophagy and apoptosis in hepatopancreas of Pacific whiteleg shrimp Litopenaeusvannamei

Oxidative stress caused by ammonia and nitrite, affect the health and growth of aquaculture animals, results in oxidative damages. However, the toxic mechanism and pathogenesis of ammonia and nitrite to aquatic invertebrates are not completely clear. The present study was conducted to investigate the effects of sub-lethal ammonia and nitrite on autophagy and apoptosis in hepatopancreas of Pacific whiteleg shrimp Litopenaeus vannamei. Shrimps were exposed to sub-lethal ammonia (20 mg/L) and nitrite (20 mg/L) for 72 h, respectively. Hepatopancreas was collected for investigating the autophagy and apoptosis under stress conditions. The results showed that ammonia stress could induce up-regulated of autophagy (ATG3, ATG4, ATG10 and ATG12) and apoptosis (Caspase3 and P53) genes transcription. Nitrite stress could also induce up-regulated of autophagy (ATG3, ATG4, ATG5 and ATG10) and apoptosis (Caspase3) genes transcription. The expression of the autophagy related genes increased at first and then decreased with increasing exposure time. The atrophy, lysis, vacuolation of cell and other tissue damages in hepatopancreas were observed after 72h exposure to ammonia and nitrite. The results indicated that ammonia and nitrite stress could induce autophagy and apoptosis, and results in oxidative damage.

The Effects of Chronic Lead Exposure on Testicular Development of Japanese Quail (Coturnix japonica): Histopathological Damages, Oxidative Stress, Steroidogenesis Disturbance, and Hypothalamus-Pituitary-Testis Axis Disruption

Lead (Pb) becomes a global public health concern for its high toxicology. Birds are sensitive to environmental pollution and Pb contamination exerts multiple negative influences on bird life. Pb also impacts on avian reproductive system. Thus, in this study, we attempted to determine toxicological effects and possible mechanistic pathways of Pb on avian testicular development by using the model species-Japanese quail (Coturnix japonica). Male quail chicks of 1-week-old were exposed to 0, 50, 500, and 1000 ppm Pb concentrations in drinking water for 5 weeks when reaching sexual maturation. The results showed that high Pb doses (500 and 1000 ppm) induced testis atrophy and cloacal gland shrinkage. Microstructural damages of both hypothalamus and testis indicated the disruption of the hypothalamus-pituitary-gonadal (HPG) axis by Pb exposure. The decrease of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and testosterone (T) may also imply HPG axis disruption. Moreover, excess testicular oxidative damages featured by increasing reactive oxygen species (ROS) and malondialdehyde (MDA) and decreasing catalase (CAT), glutathione (GSH), superoxide dismutase (SOD), glutathione-S-transferase (GST), and total antioxidant capacity (T-AOC) indicated increasing risks of reproductive dysfunction by Pb. Furthermore, increasing apoptosis and upregulation of gene expression associated with cell death suggested testicular abnormal development. In addition, molecular signaling involved with steroidogenesis in the testis was disturbed by Pb treatment. The study showed that Pb could impair testicular development and reproductive function by morphological and histological injury, hormone suppression, oxidative stress, cell death, and HPG axis disruption.

Reference dose prediction by using CDK molecular descriptors: A non-experimental method

Reference dose (RfD) is an estimate of a daily dose that individual can be exposed chronically without obvious deleterious effects during a lifetime. In the area of toxicology, researchers always use the traditional approach by employing NOAEL/LOAEL or the benchmark dose (BMD) and other dose-response approaches to estimate RfD. These methods have, despite their typicalness, certain limitations. In this study, we present a novel method of the estimation of reference dose without experiments. The information of the organic chemicals is available from the Integrated Risk Information System (IRIS) of USEPA. Molecular descriptors for each molecular structure were calculated by an integrated platform, and the chemicals were classified into four categories based on molecular similarity: 128 contained benzene rings, 47 were heteroaromatics, 104 contained halogen substituents and 44 were halogenated aliphatic hydrocarbons. The predictive model of RfD was constructed by the multiple linear stepwise regression (MLR) method. Approximately 95% and 82% of the data points differ by less than 10-fold and 5-fold between the predicted values and the true values respectively. The non-experimental method improves the estimation efficiency and has a certain reference value to predict.

Toxicity in Takifugu rubripes exposed to acute ammonia: Effects on immune responses, brain neurotransmitter levels, and thyroid endocrine hormones

Exposure to ammonia can cause convulsions, coma, and death. In this study, we investigate the effects of ammonia exposure on immunoregulatory and neuroendocrine changes in Takifugu rubripes. Fish were sampled at 0, 12, 24, 48, and 96 h following exposure to different ammonia concentrations (0, 5, 50, 100, and 150 mg/L). Our results showed that exposure to ammonia significantly reduced the concentrations of C3, C4, IgM, and LZM whereas the heat shock protein 70 and 90 levels significantly increased. In addition, the transcription levels of Mn-SOD, CAT, GRx, and GR in the liver were significantly upregulated following exposure to low ammonia concertation, however, downregulated with increased exposure time. These findings suggest that ammonia poisoning causes oxidative damage and suppresses plasma immunity. Ammonia exposure also resulted in the elevation and depletion of the T3 and T4 levels, respectively. Furthermore, ammonia stress induced an increase in the corticotrophin-releasing hormone, adrenocorticotropic hormone, and cortisol levels, and a decrease in dopamine, noradrenaline, and 5-hydroxytryptamine levels in the brain, illustrating that ammonia poisoning can disrupt the endocrine and neurotransmitter systems. Our results provide insights into the mechanisms underlying the neurotoxic effects of ammonia exposure, which helps to assess the ecological and environmental health risks of this contaminant in marine fish.

The physiological, biochemical and transcriptional responses to sulfamethoxazole in the Asian clam, Corbicula fluminea (O. F. Müller, 1774)

Sulfamethoxazole (SMX), a broad-spectrum antibiotic, has been widely used in the treatment and prevention of infection caused by bacteria in recent years. The present study was aimed to evaluate the response mechanisms to SMX stress in gills and digestive gland of Corbicula fluminea (O. F. Müller, 1774). To this end, clams were exposed to environmentally relevant concentrations of SMX (0, 1, 10 and 100 μg/L) for 7 and 28 days, and siphon behavior, tissue-specific enzymatic and transcriptional changes were assayed. Our results showed that exposure to SMX significantly suppressed filtration rate and acetylcholinesterase (AChE) activity, activated antioxidant defense system and elevated transcription of several genes related to cell apoptosis in gills and digestive gland of clams. In general, SMX at environmentally relevant concentrations exhibited a negative impact on siphon behavior and induced neurotoxicology, oxidative stress and cell apoptosis in C. fluminea. The current study will help broaden our understanding of the ecotoxicity of SMX on freshwater bivalves.

Complete mitochondrial genome sequence of a brackish water clam Corbicula japonica (Cyrenidae: Bivalvia) collected from an estuary of Gwangyang Bay in Korea

The complete mitochondrial genome of the clam Corbicula japonica is 17,432 bp in length. The sequence consists of 13 protein-coding, 2 ribosomal RNAs, and 22 transfer RNA genes (GenBank accession no. MZ895053). The proportion of base-pairs in C. japonica are A + T (70.5%) and G + C (29.5%). Phylogenetic analysis reveal C. japonica to be sister species to C. fluminea within the monophyletic genus Corbicula, with high support. This study is helpful to the classification of the brackish water clam C. japonica, which is difficult to identify during early development owing to variation of shell morphology.

Impairment of the gut health in Danio rerio exposed to triclocarban

Triclocarban (TCC) is the principal component in personal and health care products because it is a highly effective, broad-spectrum, and safe antibacterial agent. TCC has recently been discovered in aquatic creatures and has been shown to constitute a health danger to aquatic animals. Although several studies have looked into the toxicological effects of TCC on a variety of aquatic animals from algae to fish, the possible gut-toxicity molecular pathway in zebrafish has never been thoroughly explored. We investigated the gut-toxic effects of TCC on zebrafish by exposing them to different TCC concentrations (100 and 1000 μg/L) for 21 days. We discovered for the first time that the MAPK and TLR signaling pathways related to gut diseases were significantly altered, and inflammation (up-regulation of TNF-α, IL-6, and IL-1β) caused by TCC was confirmed to be largely mediated by the aryl hydrocarbon receptor (AHR) and its related cytokines. This was found using the results of qPCR, a transcriptome analysis, and molecular docking (AHR, AHRR, CYP1A1 and CYP1B1). Furthermore, high-throughput 16S rDNA sequencing demonstrated that TCC exposure reduced the bacterial diversity and changed the gut microbial composition, with the primary phyla Fusobacteria and Proteobacteria, as well as the genera Cetobacterium and Rhodobacteraceae, being the most affected. TCC exposure also caused damage to the gut tissue, including an increase in the number of goblet cells and a reduction in the height of the columnar epithelium and the thickness of the muscular layer, as shown by hematoxylin and eosin staining. Our findings will aid in understanding of the mechanism TCC-induced aquatic toxicity in aquatic species.

Changes in physiological activities are responsible for homoyessotoxin-induced toxicity in abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) is a lipid-soluble toxin produced by toxic dinoflagellates. It is widely distributed in marine ecosystems worldwide, and it poses a threat to the survival of aquatic animals. The tissues of the abalone Haliotis discus hannai are easily damaged by homo-YTX during harmful algal blooms. In this study, H. discus hannai was exposed to homo-YTX (0, 2, 5, and 10 µg L^-1) to evaluate the rates of survival (S) and death (D) and the antioxidative, metabolic, and digestive physiological responses in the gills and digestive gland of abalone. Homo-YTX decreased S and the activities of Na⁺/K⁺-adenosine triphosphatase, Ca²⁺/Mg²⁺-adenosine triphosphatase, superoxide dismutase, catalase, alkaline phosphatase, xanthine oxidase, lactate dehydrogenase, amylase, protease, and lipase. Meanwhile, D, the reactive oxygen species level, and the malondialdehyde content increased with increasing concentrations of homo-YTX. In addition, homo-YTX induced oxidative stress, enhanced the lipid peroxidation reaction, reduced the energy supply, and inhibited the metabolic and digestive physiological activities in the gills and digestive gland of abalone. Oxidative stress-mediated insufficient energy supply and physiological activity reduction caused the death of abalone.

Effects of acute ammonia nitrogen exposure on metabolic and immunological responses in the Hong Kong oyster Crassostrea hongkongensis

Ammonia nitrogen, a major oxygen-consuming pollutant in the environment, can adversely affect aquatic organisms such as fish, bivalves, and crustaceans. We investigated the toxic effects of ammonia nitrogen on the Hong Kong oyster, Crassostrea hongkongensis, using flow cytometry and ¹H nuclear magnetic resonance metabolomics. Exposure to ammonia nitrogen caused time- and concentration-dependent alterations in various immune parameters in hemocytes and impaired the metabolic profiles of the gills. We observed changes in the rate of apoptosis, esterase activity, lysosomal mass, hemocyte counts, phagocytic activity, and mitochondrial mass. Exposure affected metabolic pathways involved in energy metabolism, osmotic balance, and oxidative stress. We concluded that ammonia nitrogen induces metabolic and hematological dysfunction in C. hongkongensis, and our findings provide insights into the biochemical defense strategies of bivalves exposed to acute high-concentration ammonia nitrogen.

Contrasting tourism regimes due to the COVID-19 lockdown reveal varied genomic toxicity in a tropical beach in the Southern Atlantic

Tourist occupancy in coastal environments threatens the stability of various coastal ecosystems and is thus a cause for concern for the environmental sector. As such, it is important to perform environmental monitoring in a way that analyses and quantifies the environmental impact of coastal ecosystems. Porto de Galinhas beach (Pernambuco - Brazil) has one of the highest visitation rates in Brazil and suffered from restrictions to human mobility due to the COVID-19 pandemic. These restrictions allowed for the evaluation of the impact of tourism on Porto de Galinhas beach and the effects that the lack of tourist occupancy had during the lockdown period of 2020. Blood samples from the species Abudefduf saxatilis were collected monthly over a period of 1 year and during the lockdown quarter, in order to perform micronucleus (MN) and nuclear morphological alteration (NMA) tests, and data were analyzed at a seasonal level (dry/rainy period) using a comet assay. For the control group, A. saxatilis samples were collected in an environmentally protected area on Tamandaré beach (68 km from Porto de Galinhas). The MN and NMA tests showed a greater frequency of genomic damage when there was greater tourist flow. In relation to rain seasonality, the comet assay showed a greater incidence of genomic damage during the dry period, where there was a higher rate of tourist migration, compared to the rainy period. The lockdown period presented a lower incidence of genotoxic damage compared to the period without restrictions on human mobility and the control. The results show that tourism has been causing a significant environmental impact on Porto de Galinhas beach. The data collected during the lockdown period demonstrated how the absence of human movement results in changes that are favorable to environmental recuperation, as illustrated by the lower frequency of genomic damage.

Full-Length Transcriptome Sequencing Reveals Tissue-Specific Gene Expression Profile of Mangrove Clam Geloina erosa

Mollusca is the second largest animal phylum and represents one of the most evolutionarily successful animal groups. Geloina erosa, a species of Corbiculidae, plays an important role in mangrove ecology. It is highly adaptable and can withstand environmental pollution and microbial infections. However, there is no reference genome or full-length transcriptome available for G. erosa. This impedes the study of the biological functions of its different tissues because transcriptome research requires reference genome or full-length transcriptome as a reference to improve accuracy. In this study, we applied a combination of Illumina and PacBio single-molecule real-time sequencing technologies to sequence the full-length transcriptomes of G. erosa tissues. Transcriptomes of nine samples obtained from three tissues (hepatopancreas, gill, and muscle) were sequenced using Illumina. Furthermore, we obtained 87,310 full-length reads non-chimeric sequences. After removing redundancy, 22,749 transcripts were obtained. The average Q score of 30 was 94.48%. In total, 271 alternative splicing events were predicted. There were 14,496 complete regions and 3,870 lncRNAs. Differential expression analysis revealed tissue-specific physiological functions. The gills mainly express functions related to filtration, metabolism, identifying pathogens and activating immunity, and neural activity. The hepatopancreas is the main tissue related to metabolism, it also involved in the immune response. The muscle mainly express functions related to muscle movement and control, it contains more energy metabolites that gill and hepatopancreas. Our research provides an important reference for studying the gene expression of G. erosa under various environmental stresses. Moreover, we present a reliable sequence that will provide an excellent foundation for further research on G. erosa.

Behavioral Variables to Assess the Toxicity of Unionized Ammonia in Aquatic Snails: Integrating Movement and Feeding Parameters

Behavioral endpoints are important parameters to assess the effects of toxicants on aquatic animals. These endpoints are useful in ecotoxicology because several toxicants modify the animal behavior, which may cause adverse effects at higher levels of ecological organization. However, for the development of new bioassays and for including the behavior in ecotoxicological risk assessment, the comparison of sensitivity between different behavioral endpoints is necessary. Additionally, some toxicants remain in aquatic environments for a few hours or days, which may lead to animal recovery after toxicant exposure. Our study aimed to assess the effect of unionized ammonia on the movement and feeding behaviors of the aquatic gastropod Potamopyrgus antipodarum (Tateidae, Mollusca) and its recovery after exposure. Four treatments were used: a control and three nominal concentrations of unionized ammonia (0.25, 0.5 and 1 mg N-NH₃/L). Each treatment was replicated eight times, with six animals in each replicate. Animals were exposed to unionized ammonia for 48 h (exposure period) and, subsequently, to control water for 144 h (post-exposure period). Two movement variables were monitored without food and five feeding behavioral variables were monitored in the presence of food. Some of the feeding behavioral variables showed higher sensitivity (LOEC = 0.25-0.5 mg N-NH₃/L) than the movement behavior variables monitored without food (LOEC = 1 mg N-NH₃/L). After exposure to unionized ammonia, animals showed a recovery of most behavioral endpoints. The inclusion of post-exposure period and feeding behaviors in bioassays may make studies more realistic, which is crucial for a proper ecotoxicological risk assessment.

Behaviors and biochemical responses of macroinvertebrate Corbicula fluminea to polystyrene microplastics

Microplastic, a well-documented emerging contaminant, is widespread in aquatic environments resulting from the production and fragmentation of large plastics items. The knowledge about the chronic toxic effects and behavioral toxicity of microplastics, particularly on freshwater benthic macroinvertebrates, is limited. In this study, adult Asian clams (Corbicula fluminea) were exposed to gradient microplastic solutions for 42 days to evaluate behavioral toxicity and chronic biotoxicity. The results showed that microplastics caused behavior toxicity, oxidative stress, and tissue damage in high-concentration treatments. Siphoning, breathing, and excretion was significantly inhibited (p < 0.05) at high-concentration treatments, suggesting that high-concentration microplastics induced behavioral toxicity in C. fluminea. Malondialdehyde content, superoxide dismutase, catalase, and glutathione reductase activities were significantly enhanced (p < 0.05) and the acetylcholinesterase was significantly inhibited (p < 0.05) throughout the exposure period in high-concentration treatments. Enzymes associated with energy supply were significantly higher at high-concentration microplastics treatments on D7 and D21. However, they recovered to a normal level on D42. The instability of the enzymes indicated that high-concentration microplastics induced oxidative stress and disorder in neurotransmission and energy supply. The gills of C. fluminea in treatments underwent cilia degeneration, which indicated that microplastics caused tissue damage in the gills. The analysis of integrated biomarker response values revealed that high-concentration microplastics led to long-term effects on the health of C. fluminea. In conclusion, continuous exposure to microplastics (10 mg L^-1) would damage physical behavior and the antioxidant system of C. fluminea.

PRR-Mediated Immune Response and Intestinal Flora Profile in Soybean Meal-Induced Enteritis of Pearl Gentian Groupers, Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂

Pattern recognition receptors (PRRs) can recognize microbial-specific pathogen-associated molecular patterns, initiate signal cascade transduction, activate the expressions of host immunity and proinflammatory genes, and, ultimately, trigger an immune response against identified pathogens. The present study focused on two outcomes of feeding pearl gentian groupers with high levels of soybean meal (SBM): (1) growth performance and (2) the intestinal environment, including tissue structure, flora profile, and immune responses. Some 720 groupers were randomly divided into three groups (n = 4): (1) controls, fed a 50% fish meal feed (FM), (2) with 20% of the FM substituted with SBM (SBM20), and (3) 40% of the FM substituted with SBM (SBM40). The fish were fed these iso-nitrogenous and iso-lipidic diets for 10 weeks. They were kept in containers with 1 m3 of water under natural light and temperature levels. The experimental results demonstrate that the SBM diets significantly degraded growth performance and intestinal physiology. Typical enteritis characteristics and immune fluctuations appeared, as reflected by the enzyme activities of total superoxide dismutase and lysozyme, and the contents of immunoglobulin M, complement 3, and complement 4. 16SrDNA high-throughput sequencing showed that the intestinal flora was significantly affected, with the abundance of harmful bacteria, such as Vibrio and Streptococcus, increasing with dietary SBM level. Based on "3 + 2" full-length transcriptome sequencing, three triggered PRRs were found in the intestine: the RIG-like receptor, NOD-like receptor, and Toll-like receptor signaling pathways. The intestinal flora variations were significantly correlated with the activation of the three PRR signaling pathways by canonical correlation analysis. These culminated in the transcriptome activation of NF-κB, IRFs, and costimulatory molecules, ultimately promoting the expressions of proinflammatory cytokines, interferons (IFNs), chemokines, and other molecules vital to the innate and/or adaptive immune responses. This study provides new information for diagnosing and preventing SBMIE in aquaculture fish.

Transcriptomic analyses of the acute aerial and ammonia stress response in the gill and liver of large-scale loach (Paramisgurnus dabryanus)

The large-scale loach (Paramisgurnus dabryanus) is one of the most commercially important cultured species. Ammonia nitrogen accumulation is one of the key issue which limited production and animal health in aquaculture, but few of information is available on the molecular mechanisms of ammonia detoxification. We performed transcriptomic analyses of the gill and liver of large-scale loach subjected to 48 h of aerial and ammonia exposure. We obtained 47,473,424 to 56,791,496 clean reads from the aerial exposure, ammonia exposure and control groups, assembled and clustered a total of 92,658 unigenes with an average length of 909 bp and N50 of 1787 bp. Totals of 489/145 and 424/140 differentially expressed genes (DEGs) were detected in gill/liver of large-scale loach after aerial and ammonia exposure through comparative transcriptome analyses, respectively. In addition, totals of 43 gene ontology (GO) terms and 266 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were identified. After aerial and ammonia exposure, amino acid metabolism pathways in liver of large-scale loach were significantly enriched, suggesting that large-scale loach responded to high exogenous and endogenous ammonia stress by enhancing amino acid metabolism. Besides, the expression of several ammonia transporters (i.e., Rhesus glycoproteins and Aquaporins) in gill of large-scale loach were markedly changed after 48 h of aerial exposure, suggesting that large-scale loach responded to high endogenous ammonia stress by regulating the expression of Rh glycoproteins and Aqps related genes in gill. The results provide valuable information on the molecular mechanism of ammonia detoxification of large-scale loach to endogenous and environmental ammonia loading, will facilitate the molecular assisted breeding of ammonia resistant varieties, and will offer beneficial efforts for establishing an environmental-friendly and sustainable aquaculture industry.

Integrated physiological, transcriptome and metabolome analyses of the hepatopancreas of the female swimming crab Portunus trituberculatus under ammonia exposure

Ammonia is a common environmental pollutant in aquatic ecosystem and is also a significant concern in closed aquaculture systems. The threat of ammonia has been increasing with rising anthropogenic activities including intensified aquaculture. In this study, we aimed to investigate ammonia toxicity and metabolism mechanisms in the hepatopancreas, a major organ for Vitellogenin (Vtg) synthesis and defending against ammonia stress, of female swimming crab Portunus trituberculatus which is an important fishery and aquaculture species, by integrating physiological, transcriptome and metabolome analyses. The results revealed that ammonia exposure (10 mg/L, an environmentally relevant concentration) resulted in a remarkable reduction in vtg expression and depression of multiple signaling pathways for reproductive regulators including methyl farnesoate, ecdysone and neuroparsin, demonstrating for the first time that ammonia impairs swimming crab female reproduction. In addition, a number of important genes and metabolites in glycolysis, the Krebs cycle, fatty acid β-oxidation and synthesis were significantly downregulated, indicating that changes in ammonia levels lead to a general depression of energy metabolism in hepatopancreas. After ammonia exposure, an increased level of urea and a reduction of amino acid catabolism were observed in hepatopancreas, suggesting that urea cycle was utilized to biotransform ammonia, and amino acid catabolism was decreased to reduce endogenous ammonia generation. Furthermore, antioxidant systems were altered following ammonia exposure, which was accompanied by proteins and lipid oxidations, as well as cellular apoptosis. These results indicate that ammonia leads to metabolic suppression, oxidative stress and apoptosis in P. trituberculatus hepatopancreas. The findings improve the understanding for the mechanisms of ammonia toxicity and metabolism in P. trituberculatus, and provide valuable information for assessing potential ecological risk of environmental ammonia and improving aquaculture management.

Toxic Effects on Bioaccumulation, Hematological Parameters, Oxidative Stress, Immune Responses and Tissue Structure in Fish Exposed to Ammonia Nitrogen: A Review

Simple Summary

Ammonia nitrogen is a common environmental limiting factor in aquaculture, which can accumulate rapidly in water and reach toxic concentrations. In most aquatic environments, fish are vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. It has been found that the toxic effects of ammonia nitrogen on fish are multi-mechanistic. Therefore, the purpose of this review is to explore the various toxic effects of ammonia nitrogen on fish, including oxidative stress, neurotoxicity, tissue damage and immune response.

Abstract

Ammonia nitrogen is the major oxygen-consuming pollutant in aquatic environments. Exposure to ammonia nitrogen in the aquatic environment can lead to bioaccumulation in fish, and the ammonia nitrogen concentration is the main determinant of accumulation. In most aquatic environments, fish are at the top of the food chain and are most vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. In fish exposed to toxicants, ammonia-induced toxicity is mainly caused by bioaccumulation in certain tissues. Ammonia nitrogen absorbed in the fish enters the circulatory system and affects hematological properties. Ammonia nitrogen also breaks balance in antioxidant capacity and causes oxidative damage. In addition, ammonia nitrogen affects the immune response and causes neurotoxicity because of the physical and chemical toxicity. Thence, the purpose of this review was to investigate various toxic effects of ammonia nitrogen, including oxidative stress, neurotoxicity and immune response.