Characterizations of intracellular copper/zinc superoxide dismutase from yellow drum (Nibea albiflora, Richardson 1846) and its gene expressions under the ammonia/nitrite stress

Ecological risks of high-ammonia environment with inhibited growth of Daphnia magna: Disturbed energy metabolism and oxidative stress

High ammonia pollution is a common problem in water bodies. However, research on the mechanisms underlying the toxic effects on organisms at different nutritional levels is still insufficient. Herein, based on the environmental concentration, the toxic effects of high ammonia pollution on Daphnia magna were investigated. Overall, the feeding and filtration rates of D. magna were significantly decreased by ammonia. Growth inhibition of D. magna by ammonia was confirmed by the decreased body length. After ammonia exposure, the metabolic status of D. magna changed, the correlation network weakened, and the correlations between metabolites were disrupted. Changes occurred in metabolites primarily involved in oxidative stress, fatty acid oxidation, tricarboxylic acid cycle, and protein digestion, absorption, and synthesis, which were validated through alterations in multiple biomarkers. In addition, mitochondrial function was evaluated and was found to inhibit mitochondrial activity, which was accompanied by a decreased marker of mitochondrial activity contents and ATPase activity. Thus, the results suggested that energy metabolism and oxidative stress were involved in ammonia-induced growth toxicity. This study provides new insights into the impact of ammonia on aquatic ecological health.

Combined effects of hypoxia and ammonia-N exposure on the oxygen consumption, glucose metabolism and amino acid metabolism in hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂)

This study evaluated the influence of hypoxia and ammonia-N co-exposure on oxygen consumption, glucose metabolism and amino acid metabolism in hybrid grouper. The results showed that elevated expression of GLUT1, MCT1, PFK, HK and LDH were induced by co-exposure to hypoxia and ammonia. In addition, co-exposure to hypoxia and ammonia reduced the tolerance of hybrid grouper to ammonia-N. Furthermore, ammonia-N exposure caused an increase in oxygen consumption in hybrid grouper. After ammonia-N exposure for 96 h, 10 amino acids contents and activities of AST and ALT elevated in hybrid grouper muscle. The study revealed that combined exposure to hypoxia and ammonia-N significantly increased glucose metabolism, oxygen consumption and amino acid metabolism in hybrid grouper, and presented significant synergistic effects.

Transcriptome analysis revealed the mechanism of Luciobarbus capito (L. capito) adapting high salinity: Antioxidant capacity, heat shock proteins, immunity

Salinity has a significant influence on the physiology of freshwater aquatic organisms. However, there are few studies on the hematology and immunology of freshwater fish under high salinity. In the current study, we aimed to analyze the adaptive effect of salt stress on L. capito spleen immune function and hematology using transcriptomic analysis. We replicated a L. capito acute salinity stress model, and collected blood and spleens from freshwater and saltwater fish. It was found that salinity affected significantly the numbers of leukocytes, lymphocytes, neutrophils, and red blood cells, as well as the content of haemoglobin. Salt treatment resulted in a significant increase in the expression of HSP70, HSP90, CAT, SOD, and GPX1 genes in L. capito spleens. Transcriptomic analysis revealed a total of 546 differentially expressed genes (DEGs) in spleens, including 224 up-regulated DEGs and 322 down-regulated DEGs. In addition, GO enrichment analysis revealed immune system process, multicellular organismal process, and biological regulation of genes with the most differences in biological processes. KEGG enrichment analysis showed that the regulation of lipolysis in adipocyte, FoxO signaling pathway, Hematopoietic cell lineage signaling pathway, and HIF-1 signaling pathway were significantly enriched. L. capito adapted oxidative to high salinity through FoxO signaling pathway and immune to high salinity through Hematopoietic cell lineage signaling pathway. At the same time, we selected 10 DEGs for qRT-PCR detection, and the results showed that the qRT-PCR results were consistent with our RNA-Seq results, indicating that transcriptome sequencing was accurate and reliable. In conclusion, our results demonstrated that the improvement of antioxidant capacity, heat shock protein and immunity are involved in the molecular mechanism of L. capito adapting to high salinity. Our findings provided a rationale for further study on high salinity adaptation and related enrichment pathways.

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.

Ficus hirta Vahl. promotes antioxidant enzyme activity under ammonia stress by inhibiting miR-2765 expression in Penaeus vannamei

Ficus hirta Vahl. has been reported to have hepatoprotective, antitumor, antibacterial functions, and is used to treat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Ammonia nitrogen is one of the most common environmental stress factors in aquaculture. Long-term exposure to high concentrations of ammonia nitrogen can induce oxidative stress and increase the risk of infections. However, whether Ficus hirta Vahl. has effect on ammonia nitrogen stress is unclear. In present study we report that Ficus hirta Vahl. improves the activity of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) of shrimp and decreases shrimp mortality caused by ammonia nitrogen stress. It is demonstrated that miR-2765 is negatively regulate the antioxidant capacity. We find that SOD was a direct target gene of miR-2765. MiR-2765 can bind to 3'-untranslated region (3'-UTR) of SOD to inhibit its transcription. Furthermore, Ficus hirta Vahl. down-regulates miR-2765 to activate the antioxidant capacity to alleviate the damage caused by ammonia nitrogen stress. Interestingly, overexpression of miR-2765 could attenuate the protective effect of Ficus hirta Vahl. on shrimp under ammonia nitrogen stress. These data indicate that Ficus hirta Vahl. alleviates the damage of ammonia nitrogen stress in shrimp by repressing miR-2765 and activating the antioxidant enzyme system. This study will provide a theoretical basis and a new perspective for assessing the toxicity mechanism of ammonia nitrogen in the process of farming on shrimp.

Superoxide Dismutase Multigene Family from a Primitive Chondrostean Sturgeon, Acipenser baerii: Molecular Characterization, Evolution, and Antioxidant Defense during Development and Pathogen Infection

Three distinct superoxide dismutases (SODs)-copper/zinc-SOD (SOD1), manganese-SOD (SOD2), and extracellular copper/zinc-SOD (SOD3)-were identified from a primitive chondrostean fish, Acipenser baerii, enabling the comparison of their transcriptional regulation patterns during development, prelarval ontogeny, and immune stimulation. Each A. baerii SOD isoform (AbSOD) shared conserved structural features with its vertebrate orthologs; however, phylogenetic analyses hypothesized a different evolutionary history for AbSOD3 relative to AbSOD1 and AbSOD2 in the vertebrate lineage. The AbSOD isoforms showed different tissue distribution patterns; AbSOD1 was predominantly expressed in most tissues. The expression of the AbSOD isoforms showed isoform-dependent dynamic modulation according to embryonic development and prelarval ontogenic behaviors. Prelarval microinjections revealed that lipopolysaccharide only induced AbSOD3 expression, while Aeromonas hydrophila induced the expression of AbSOD2 and AbSOD3. In fingerlings, the transcriptional response of each AbSOD isoform to bacterial infection was highly tissue-specific, and the three isoforms exhibited different response patterns within a given tissue type; AbSOD3 was induced the most sensitively, and its induction was the most pronounced in the kidneys and skin. Collectively, these findings suggest isoform-dependent roles for the multigene SOD family in antioxidant defenses against the oxidative stress associated with development and immune responses in these endangered sturgeon fish.