Impact of nitrite exposure on plasma biochemical parameters and immune-related responses in Takifugu rubripes

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.

Preliminary Study to Assess the Impact of Dietary Rutin on Growth, Antioxidant Capacity, and Intestinal Health of Yellow Catfish, Pelteobagrus fulvidraco

This research aimed to examine the effects of dietary rutin supplementation on growth, body composition, serum biochemical indexes, liver enzyme activities and antioxidant-related genes expression, intestinal morphology, and microbiota composition of juvenile yellow catfish (Pelteobagrus fulvidraco). Rutin was added to the basal diets at doses of 0 (control), 100 mg/kg, and 500 mg/kg. Each diet was fed randomly into three tanks, each tank containing 30 fish with an initial body mass of (10.27 ± 0.62) g. The feeding trial was conducted in an indoor recirculating aquiculture system at 28 °C for 56 days. According to the findings, the inclusion of 100 mg/kg rutin significantly improved the growth performance of yellow catfish and reduced the feed conversion ratio; however, the growth promotion effect was diminished when the diet was supplemented with 500 mg/kg of rutin. The inclusion of 500 mg/kg rutin in the diet significantly reduced the level of crude lipid and protein of the whole fish. Serum activities of alkaline phosphatase, albumin, and total protein were all significantly increased when fish were fed the diet supplemented with 500 mg/kg rutin, while serum glucose was significantly lower compared to the control group. Meanwhile, dietary rutin at a concentration of 500 mg/kg significantly induced the hepatic mRNA expressions of antioxidant-related genes (including Cu/Zn-SOD, Mn-SOD, CAT, GPx) and inflammatory-associated genes (including TNFα, IL-10, LYZ). Incorporating rutin at doses of 100 mg/kg and 500 mg/kg into the diets resulted in a notable increase in superoxide dismutase (SOD) activity, while simultaneously reducing malondiadehyde (MDA) content in the liver and intestine. Intestinal villus height, villus width, muscular thickness, and lumen diameter were significantly increased with the administration of 500 mg/kg of dietary rutin. Gut microbial diversity analysis indicated that supplementing diets with 100 mg/kg and 500 mg/kg rutin significantly enhanced the abundance of Cetobacterium while decreasing Plesiomonas richness. In conclusion, dietary rutin levels at 100 mg/kg could enhance the growth, antioxidant capability, and intestinal health of yellow catfish under present experimental conditions.

Exploring the effect of Ulva prolifera decay on the immune tissue of Paralichthys olivaceus based on transcriptomics and histopathological analysis

For 17 consecutive years, the outbreak of Ulva prolifera in the South Yellow Sea area of China has caused significant negative impacts on coastal ecological environment. However, its specific influence on fish immunity is rare. In this study, the juvenile Paralichthys olivaceus was exposed to fresh U. prolifera algae (FU) and decomposing algal effluent (DU). After short-term stress for 14 days, the histopathological and transcriptome analysis were performed to study the effect of U. prolifera decay on P. olivaceus. Histopathological analysis found that the liver, spleen and head kidneys of P. olivaceus were damaged after the short-term stress. The transcriptome results showed that the steroid biosynthesis signaling pathway and the PI3K-Akt signaling pathway were significantly enriched. Some immune related genes, including c1qc-like, dusp1, dusp16, HSP90 and metabolic related genes serotransferrin, were differentially expressed. These results highlighted the harmfulness of U. prolifera on marine fish, setting a solid foundation for further analyses.

Apoptotic Changes, Oxidative Stress and Immunomodulatory Effects in the Liver of Japanese Seabass (Lateolabrax japonicus) Induced by Ammonia-Nitrogen Stress during Keep-Live Transport

This study investigated the effects of NH₃-N on antioxidant responses, histoarchitecture, and immunity of Japanese seabass (Lateolabrax japonicus) during keep-live transport. The findings suggest that NH₃-N stress transport alters the transcription of P53, Caspase 9, Bcl2, Caspase 3 and Bax genes, demonstrating that NH₃-N stress can trigger the apoptotic pathway of P53-Bax-Bcl2 and Caspase and induce apoptosis. NH₃-N stress transport also evoked transcriptional upregulation of inflammatory cytokines (tumor necrosis factor α (TNF-α), Toll-like receptor 3 (TLR-3), nuclear factor kappa β (NF-κB), interleukin 6 (IL-6) and interleukin 1β (IL-1β)) and increased complement C3, C4, lysozyme (LZM) and immunoglobulin (IgM) levels, activating the innate immunological system during keep-live transport. In addition, NH₃-N stress transport altered changes in the levels of superoxide dismutase (SOD), catalase (CAT), glutathione-related enzymes, and heat shock proteins 70 and 90 in the liver, indicating that the antioxidant system and Hsp protected the cells from NH₃-N-induced oxidative stress. When excess ROS were not removed, they caused the body to respond with immunological and inflammatory responses, as well as apoptosis and tissue damage. This helps towards understanding the effect of NH₃-N levels on sea bass during keep-live transport.

The IL17 signaling pathway: A potential signaling pathway mediating gill hyperplasia and inflammation under ammonia nitrogen stress was identified by multi-omics analysis

Ammonia nitrogen is extremely toxic to aquatic animals, and is also the most common pollutant in the aquatic environment. In order to investigate the effect of high concentration of ambient ammonia nitrogen on fish gills, two groups, including a high ammonia group (T group: TAN = 2.5 mg/L, 10 % 96 h LC50) and a control group (Z group: total ammonia nitrogen (TAN) = 0 mg/L) were set up in this study. The effects of chronic ammonia stress on the gills of Pelteobagrus fulvidraco were investigated by histopathological, enzymatic, transcriptomic and proteomic analyses after 28 d of stress at different ammonia nitrogen concentrations. Histopathological observations revealed significant inflammatory cell infiltration, necrotic and abscission at the base of the gill filaments, and massive proliferation of cells at the base of the gill lamellae. Ammonia nitrogen stress led to increased reactive oxygen species (ROS) content and decreased catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX) activities in gills, indicating significant oxidative stress in gills. And further transcriptomic analysis revealed that 807 differential expression genes (DEGs) were generated in the gills, of which 587 DEGs were up-regulated and 220 DEGs were down-regulated. In addition, proteomics analysis identified 1073 differential expression proteins (DEPs) in gills, including 983 up- and 90 down-regulated DEPs. Pathway enrichment analysis of the DEGs and DEPs revealed that multiple inflammation-related signaling pathways were activated in the gill, including the significantly enriched IL17 signaling pathway. This suggests that IL17 signaling pathway might have a significant impact during signaling transduction. Further analysis of network regulation by mapping DEGs and DEPs to KEGG pathway revealed that IL17 signaling pathway mediated inflammation and cell proliferation in gills under ammonia stress. The results of this study provided new insights into the response of fish gills to ammonia nitrogen stress, and the IL17 signaling pathway may be a potential therapeutic target for reducing ammonia nitrogen gill toxicity.

Impact of nitrite exposure on oxidative stress and antioxidative-related genes responses in the gills of Procambarus clarkii

Nitrite is the major environmental pollutant in the freshwater aquaculture environment, which has a negative impact on aquatic species growth. Currently, we know that the main way nitrite enters crustaceans is through their gills. In this study, a total of 96 h acute nitrite stress (60 mg/L) experiments were conducted, and the impact of the serum biochemical parameters, gill oxidase activity and oxidative-related gene expression of red swamp crayfish were evaluated. After exposure to nitrite for 0, 6, 12, 24, 48, and 96 h, hemolymph and gills samples were taken at each time point. In the serum, acute nitrite stress significantly increased glutamic-oxaloacetic transaminase (GOT) and alanine aminotransferase (ALT) activities after 6 h of exposure, decreased total protein (TP) and albumin (ALB) levels after 24 h and 48 h of exposure, respectively. In the gills, the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were enhanced to the maximum level at 12 h, 24 h and 24 h, respectively. The contents of malondialdehyde (MDA) and lipid peroxide (LPO) were increased significantly after 12 h and 24 h exposure, respectively. In addition, the expression levels of antioxidative-related genes, including hsp70, fer and mt, were significantly upregulated in the gills after 6 h of exposure. The results indicated that acute nitrite stress changed the serum physiological status, induced oxidative stress and caused damage to gill cells in P. clarkii.

Acute nitrite exposure-induced oxidative damage, endoplasmic reticulum stress, autophagy and apoptosis caused gill tissue damage of grass carp (Ctenopharyngodon idella): Relieved by dietary protein

Nitrite poses a serious threat to intensive aquaculture. Protein, as a major nutrient in animals, is vital for protecting animal tissues from damage. In this study, we investigated the protective effect of dietary protein on gill tissue structure and the underlying mechanisms in sub-adult grass carp (Ctenopharyngodon idella) exposed to nitrite stress. Six iso-energetic semi-purified diets containing different protein levels (16-31 %) were formulated, and fed to fish for 60 d. The fish were then exposed to a nitrite solution for 4 d. Histopathological observation and determination of related indices (serum glucose, serum cortisol, nitric oxide, peroxynitrite, reactive oxygen species, malondialdehyde, and protein carbonyl) showed that 22-25 % dietary protein significantly alleviated the nitrite-induced stress response, gill tissue damage and oxidative damage. Further research found that a suitable dietary protein suppressed the nitrite-induced endoplasmic reticulum stress (ERS) 78 kDa glucose-regulated protein (GRP78) related signaling pathway which possibly activated autophagy and apoptosis. Interestingly, we discovered that proper dietary protein reduced autophagy, probably through unc-51-like kinase 1 (Ulk1), BCL-2-interacting myosin-like coiled-coil protein (Beclin1), autophagy-related gene 5 (Atg5), Atg12, microtubule-associated protein1 light chain 3 (LC3), BCL-2 interacting protein 3 (BNIP3) and autophagy receptor P62 (p62). We also found that an appropriate dietary protein inhibited nitrite-induced apoptosis via mitochondrial and death receptor pathways. In summary, our findings are the first to demonstrate that 22-25 % of dietary protein levels can play a protective role against nitrite-induced gill injury.

Intestinal changes associated with nitrite exposure in Bufo gargarizans larvae: Histological damage, immune response, and microbiota dysbiosis

Nitrite is a ubiquitous toxic compound in aquatic ecosystems and has negative effects on aquatic organisms. The intestine and the trillions of microbes that inhabit it, play an integral role in maintaining digestive and immune functions. However, the effects of nitrite on intestinal health and microflora have been poorly investigated. Therefore, the present study evaluated the response of intestinal histology, immunity, digestive enzyme activities and microbiota to nitrite exposure in Bufo gargarizans tadpoles. The results showed that nitrite caused damage to the intestine and impaired digestive performance. Significant changes in the transcriptional profiles of genes involved in oxidative stress (sod, gpx and hsp), inflammation, and immunity (socs3, il-27, il-1β and il-17d) were observed in the NO₂-N treatment groups. In addition, exposure to nitrite induced alterations of intestinal microbial diversity, structure and composition, suggesting that nitrite may lead to intestinal microbiota dysbiosis. It is noteworthy that probiotics (e.g., Bacteroidetes and Fusobacteria) were decreased after exposure to nitrite, whereas potentially opportunistic pathogens such as Proteobacteria and Enterobacteriaceae were elevated. Functional prediction and correlation analysis suggested that the above changes may interfere with metabolic function and trigger various diseases. Taken together, we concluded that nitrite exposure induced intestinal microbial dysbiosis, which may lead to immune dysfunction and metabolic disorder, and ultimately to histological damages in B. gargarizans. Further, this study will provide a scientific basis for further understanding the risk of nitrite pollution on the intestinal health of amphibians.

Analysis of Acute Nitrite Exposure on Physiological Stress Response, Oxidative Stress, Gill Tissue Morphology and Immune Response of Large Yellow Croaker (Larimichthys crocea)

Nitrite is a common pollutant in aquaculture water, and nitrite toxicity that negatively affects aquatic species is common in aquaculture systems when the water quality is low. Therefore, the present research aimed to evaluate the effect of acute nitrite exposure on the hematological parameters, antioxidant enzymes, immune response, and gill morphology of large yellow croaker (Larimichthys crocea). The fish were randomly separated and exposed to four (i.e., 0, 29.36, 58.73, and 88.09 mg/L) nitrite concentrations for 48 h. The fish blood and gills were collected at 0, 12, 24, 36, and 48 h of nitrite exposure for further analysis. In hematological parameters, the results showed that the levels of hemoglobin, triglyceride, and total cholesterol in blood significantly decreased (p < 0.05) in all nitrite-treated samples after 12 h, while the contents of methemoglobin in blood significantly increased (p < 0.05) in these treatments. After 48 h of nitrite exposure, the levels of cortisol in serum showed a 94.5%, 132.1%, and 165.6% increase in fish exposed to 29.36, 58.73, and 88.09 mg/L nitrite, respectively. The nitrite (i.e., 29.36, 58.73, and 88.09 mg/L) exposure significantly increased (p < 0.05) the levels of antioxidant enzymes (i.e., catalase and glutathione) in the gill and serum after 12 h of exposure compared with the control. The lysozyme levels in serum decreased in the nitrite (i.e., 29.36, 58.73, and 88.09 mg/L) exposure samples. It was found that immunoglobulin levels in the 29.36, 58.73, and 88.09 mg/L nitrite-treated samples (i.e., 1.86, 1.58, and 0.74 μg/mL, respectively) were lower than that of the control (2.56 μg/mL). In addition, the surface of the gill lamellae displayed deformation and contraction after 48 h of nitrite, especially in the fish exposed to 88.09 mg/L nitrite. These results indicate that the nitrite exposure induced the oxidative stress, affected the immune response, and changed the gill morphology, leading to nitrite poisoning in large yellow croaker.

Bioaccumulation of manganese and its effects on oxidative stress and immune response in juvenile groupers (Epinephelus moara ♀ × E. lanceolatus ♂)

We evaluated the effects of Mn in juvenile Yunlong groupers (Epinephelus moara ♀ × E. lanceolatus ♂). The groupers were exposed to Mn²⁺ (0, 0.5, 1, 2, and 4 mg/L) for 30 days after which they were assessed. The results indicate the accumulation of Mn in fish depended on dose and time. Mn²⁺ accumulation in tissues occurred in the following order: liver > gills > intestine > muscle. The concentrations of SOD and CAT in the fish significantly increased after 10 and 20 days of treatment with 4 mg/L Mn²⁺ but decreased after 30 days. Similarly, GSH and GPx levels increased after 10 days of exposure to 2 and 4 mg/L Mn²⁺ but decreased after 20 and 30 days of exposure. Additionally, malondialdehyde levels significantly increased after exposing the fish to 2 and 4 mg/L Mn²⁺ for 10, 20, and 30 days. In addition, liver HSP70 and HSP90 levels significantly increased at days 20 and 30 in all fish exposed to Mn²⁺. In addition, when Mn²⁺ concentration was 1, 2, and 4 mg/L, liver C3 and C4 levels were significantly increased after 10, 20, and 30 days. Conversely, the levels of LZM and IgM significantly decreased. Mn²⁺ also significantly upregulated the expression of genes associated with immunity (tlr3, tnf-α, il-1β, and il-6) in the fish, which suggests that it induces immunotoxicity by altering the immune response. Overall, the findings showed that Mn²⁺ can disrupt grouper health by bioaccumulating in the fish and subsequently inducing oxidative stress and immune responses. These results can help elucidate the mechanism by which manganese induces toxicity in marine fish. Additionally, they provide a new perspective regarding the detrimental effects of heavy metals in fish.

Toxic Effects on Oxidative Stress, Neurotoxicity, Stress, and Immune Responses in Juvenile Olive Flounder, Paralichthys olivaceus, Exposed to Waterborne Hexavalent Chromium

Simple Summary

Metals such as chromium can be exposed at high levels in the marine environment, and exposure to these heavy metals can have a direct effect on marine organisms. High levels of chromium exposure can have a direct impact on organisms in a coastal cage and terrestrial aquaculture. Hexavalent chromium exposure of more than 1.0 and 2.0 mg Cr⁶⁺/L induced physiological responses such as antioxidant, neurotransmitter, immune, and stress indicators in Paralichthys olivaceus. Therefore, this study will provide a reference indicator for stable aquaculture production through reference indicators for toxicity due to chromium exposure that may exist in the marine environment.

Abstract

Juvenile Paralichthys olivaceus were exposed to waterborne hexavalent chromium at various concentrations (0, 0.5, 1.0, and 2.0 mg/L) for 10 days. After chromium exposure, the activities of superoxide dismutase and glutathione S-transferase, which are oxidative stress indicators, were significantly increased; however, the glutathione level was significantly reduced. Acetylcholinesterase activity as a neurotoxicity marker was significantly inhibited upon chromium exposure. Other stress indicators, including plasma cortisol and heat shock protein 70, were significantly increased. The immune response markers (lysozyme and immunoglobulin M) were significantly decreased after chromium exposure. These results suggest that exposure to environmental toxicity in the form of waterborne chromium at concentrations higher than 1.0 mg/L causes significant alterations in antioxidant responses, neurotransmitters, stress, and immune responses in juvenile olive flounders. This study will provide a basis for an accurate assessment of the toxic effects of hexavalent chromium on aquatic organisms.

Effects of Nitrite Exposure on the Hematological Properties, Antioxidant and Stress Responses of Juvenile Hybrid Groupers, Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀

Nitrite concentrations can reach high levels in indoor aquaculture systems, thus it is vital to determine the nitrite tolerance of aquaculture fish species. Here, juvenile hybrid groupers (Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀, Family: Serranidae) were exposed to waterborne nitrite at 0, 10, 20, 40, and 80 mg NO₂⁻/L for 2 weeks. Nitrite exposure caused significant reductions in hematocrit and hemoglobin levels, significant increases in plasma calcium and plasma ALP levels, but had no significant effects on magnesium and total protein levels. Of the antioxidant responses investigated, SOD activity increased significantly in the liver and gills, but GST activity and GSH levels were significantly inhibited by nitrite exposure. Stress indicators, such as plasma cortisol and HSP 70 levels, were significantly stimulated by nitrite exposure. In brief, nitrite exposure over 20 mg NO₂⁻/L had toxic effects and affected the hematological properties, antioxidant responses, and stress indicators of juvenile hybrid groupers.

Contributing factors common to COVID‑19 and gastrointestinal cancer

The devastating complications of coronavirus disease 2019 (COVID-19) result from the dysfunctional immune response of an individual following the initial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Multiple toxic stressors and behaviors contribute to underlying immune system dysfunction. SARS-CoV-2 exploits the dysfunctional immune system to trigger a chain of events, ultimately leading to COVID-19. The authors have previously identified a number of contributing factors (CFs) common to myriad chronic diseases. Based on these observations, it was hypothesized that there may be a significant overlap between CFs associated with COVID-19 and gastrointestinal cancer (GIC). Thus, in the present study, a streamlined dot-product approach was used initially to identify potential CFs that affect COVID-19 and GIC directly (i.e., the simultaneous occurrence of CFs and disease in the same article). The nascent character of the COVID-19 core literature (~1-year-old) did not allow sufficient time for the direct effects of numerous CFs on COVID-19 to emerge from laboratory experiments and epidemiological studies. Therefore, a literature-related discovery approach was used to augment the COVID-19 core literature-based ‘direct impact’ CFs with discovery-based ‘indirect impact’ CFs [CFs were identified in the non-COVID-19 biomedical literature that had the same biomarker impact pattern (e.g., hyperinflammation, hypercoagulation, hypoxia, etc.) as was shown in the COVID-19 literature]. Approximately 2,250 candidate direct impact CFs in common between GIC and COVID-19 were identified, albeit some being variants of the same concept. As commonality proof of concept, 75 potential CFs that appeared promising were selected, and 63 overlapping COVID-19/GIC potential/candidate CFs were validated with biological plausibility. In total, 42 of the 63 were overlapping direct impact COVID-19/GIC CFs, and the remaining 21 were candidate GIC CFs that overlapped with indirect impact COVID-19 CFs. On the whole, the present study demonstrates that COVID-19 and GIC share a number of common risk/CFs, including behaviors and toxic exposures, that impair immune function. A key component of immune system health is the removal of those factors that contribute to immune system dysfunction in the first place. This requires a paradigm shift from traditional Western medicine, which often focuses on treatment, rather than prevention.

Inflammatory responses associated with hyposaline stress in gill epithelial cells of the spotted scat Scatophagus argus

The molecular processes of immune responses in mucosal tissues such as fish gills under environmental stress are poorly understood. In the present study, pro-inflammatory response under hyposaline stress and its regulation by cortisol/corticosteroid receptors (CRs) in gill epithelial cells of the spotted scat Scatophagus argus were analyzed. The fish were transferred to freshwater for 6 days (144 h) of acclimation. Following freshwater exposure, the cortisol concentration increased transiently before returning to the control level over time. mRNA expression of pro-inflammatory cytokines (TNF-a, IL-1b and IL-6) was stimulated by cortisol through CR signals at early stages of acclimation, but hyposaline stress inhibited their levels by the end of the experimental period. The transcriptional profile of anti-inflammatory cytokine IL-10 was quite different from these pro-inflammatory cytokines, and its value fluctuated within a narrow range during the experimental period. Full-length cDNAs of mineralocorticoid receptor (MR) and glucocorticoid receptor 1 (GR1) (different kinds of CRs) were cloned from the gills. Our results showed that MR and GR displayed mutually antagonistic effects during hyposaline stress. MR responded quickly at early stages, and its expression decreased with the drop of cortisol concentration. By contrast, GR expression was maintained at high levels after the acclimation of freshwater exposure. The tight coordination of GR and MR helps to shape the effects of stress on the immune system, which in turn, regulates the stress response. Our results confirm the interaction between endocrine and cytokine messengers and a clear difference in the sensitivity of GR and MR during the hyposaline challenge in gill epithelial cells of the spotted scat Scatophagus argus.

Alterations in hematological and biochemical parameters, oxidative stress, and immune response in Takifugu rubripes under acute ammonia exposure

Ammonia is a major pollutant in aquatic environments and poses a considerable threat to the survival of fish. In this study, we investigated the toxic effects of ammonia on the hematological and biochemical parameters, oxidative stress, and immune responses in Takifugu rubripes. Juvenile T. rubripes (average weight 246.17 ± 3.54 g) were exposed to different concentrations of ammonia (0, 5, 50, 100, and 150 mg/L) for 96 h. The results showed that the hematological parameters (hemoglobin, hematocrit, red blood cell, and white blood cell count) were significantly reduced in response to ammonia exposure. Of the plasma components, such as serum total protein, albumin, glucose, glutamic-oxalacetic transaminase, and glutamic-pyruvic transaminase, were significantly altered in response to ammonia exposure. Additionally, the levels of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and glutathione peroxidase (GPx) were increased after exposure to low concentration ammonia exposure. However, when fish were exposed to a high concentration of ammonia, these parameters showed the opposite trend, suggesting that an increase in antioxidant enzymes during the early stages of ammonia exposure may contribute to the removal of the induced reactive oxygen species (ROS) and protect the cells from oxidative damage. However, as the ammonia concentration and exposure time increased, the overproduction of ROS accelerated the depletion of antioxidant enzymes. Ammonia exposure significantly increased the expression of heat shock proteins (HSP70 and HSP90). Ammonia poisoning elevated gene expressions of TLR-3, TNF-α, IL-6, IL-12, and IL-1β in the gills, causing an inflammatory response. Our findings provide new insights into the mechanisms involved in ammonia-induced aquatic toxicology in marine fish, which may aid in their captive management.

Effects of the tributyltin on the blood parameters, immune responses and thyroid hormone system in zebrafish

Tributyltin (TBT) is a widely used organotin compound around the world and was frequently detected in surface waters, which would pose risk to aquatic organisms. However, the mechanisms of TBT-induced toxicity is not full clear. The present study investigated the effects of the tributyltin (TBT) on the blood parameters, immune responses and thyroid hormone system in zebrafish. Fish were exposed to sublethal concentrations of TBT (10 ng/L, 100 ng/L and 300 ng/L) for 6 weeks. The effects of long-term exposure to TBT on blood parameters (NH3, ammonia; GLU, glucose; TP, total proteins; CK, creatine kinase; ALT, alanine aminotransferase; AST, aspartate aminotransferase), immune responses (Lys, lysozyme; IgM, immunoglobulin M) and some indexes related thyroid hormone system (T3, 3,5,3'-triiodothyronine; T4, thyroxine) were measured in zebrafish, as well as the expression of genes related to immune responses and thyroid hormone system. Based on the results, the physiological-biochemical responses was significantly enhanced with an increase in TBT concentration, reflected by the abnormal blood indices, dysregulation of endocrine system and immunotoxicity in zebrafish under TBT stress. The present study greatly extends our understanding of adverse effects of TBT on aquatic organisms.

Acute Exposure to key Aquaculture Environmental Stressors Impaired the Aerobic Metabolism of Carassius auratus gibelio

Carassius auratus gibelio is an omnivore favored for its flavor and is commonly used as a benthic species in traditional pond polyculture. This study investigated the effects of common aquaculture stressors, such as high ammonia, high nitrite, high pH, and hypoxia on the aerobic metabolism of C. auratus gibelio. The results showed that the standard metabolic rate (SMR) was positively correlated with ammonia, nitrite, and pH, while the maximum metabolic rate (MMR) was negatively correlated with all four stressors. Thus, aerobic scope (AS) was reduced when C. auratus gibelio was exposed to high ammonia, high nitrite, high pH, and hypoxia. The peak of post-prandial O₂ consumption was positively correlated with nitrite, pH, and the occurrence of the peak metabolic rate post-prandial was delayed in high ammonia, high nitrite, hypoxia, and high pH conditions. These findings indicated that, in experimental conditions, exposure to these environmental stressors can influence aerobic metabolism in C. auratus gibelio. With more energy required to maintain standard metabolic rates, less will be available for growth. While the C. auratus gibelio is one of the most hypoxia tolerance species, the reduction we observed in AS caused by stressors that commonly occur in ponds and in nature will likely affect growth in ponds and fitness in nature. These data have provided insight into the optimal, fitness-maximizing thresholds for these common stressors in this species of interest.