In this study, the impact of ammonia nitrogen stress on juvenile four-finger threadfin in pond culture was examined. The 96-hour median lethal concentration (LC50-96h) and safe concentration of ammonia nitrogen were assessed in juveniles with a body weight of 7.4 ± 0.6 g using ecotoxicological methods. The study design included a stress group exposed to LC50-96h levels of ammonia nitrogen and a control group without ammonia nitrogen exposure. To examine the physiological, biochemical, and metabolic effects of ammonia nitrogen on gill tissue, gill tissue samples were collected after 12, 24, 48, and 96 h of stress, with a resumption of treatment after 48 h. Compared to the control group, ammonia nitrogen adversely affected juvenile four-finger threadfin, with LC50-96h and safe concentration values of 20.70 mg/L and 2.07 mg/L, respectively. Exposure to ammonia nitrogen resulted in substantial gill damage, including fusion of lamellae, epithelial cell loss, and proliferation of chlorine-secreting cells. This tissue damage persisted even after a 48-h recovery period. Ammonia nitrogen stress triggered an increase in antioxidant enzyme activity (superoxide dismutase, catalase, and glutathione peroxidase) and malondialdehyde levels in gills, indicating oxidative stress from 12 h onwards. Although enzyme activity decreased over time, oxidative stress persisted even after recovery, suggesting an ongoing need for antioxidant defense. Metabolomics analysis showed significant alterations in 423 metabolites under ammonia nitrogen stress. Key metabolites such as L-arginine, taurine, 20-hydroxyarachidonic acid, 11,12-dihydroxy-5Z, 8Z, and 14Z eicosotrienic acid followed an increasing trend; uridine, adenosine, L-glutathione, and thymidine 5′-triphosphate followed a decreasing trend. These changes reflect metabolic adaptations to stress. In enriched metabolic pathways, the main differential pathways are membrane transport, lipid metabolism, and amino acid metabolism. After 48 h, significant differences were observed in 396 metabolites compared to the control group. Notably, L-arginine, choline, and L-histidine increased, while linoleic acid, adenosine, and glutathione decreased. Amino acid and lipid metabolism pathways were key affected pathways. Under ammonia nitrogen stress, juvenile four-finger threadfin increased the synthesis of unsaturated and saturated fatty acids to cope with low temperatures and bolster immune function by consuming spermidine. This adaptation helps to clear peroxides generated during fatty acid synthesis, thereby protecting cells from oxidative damage. This study provides insights for pond aquaculture and breeding of ammonia nitrogen-tolerant fish strains.

中文翻译：

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氨氮胁迫对四指鱼幼鱼鳃组织生理生化及代谢水平的影响


在这项研究中，研究了氨氮胁迫对池塘养殖四指丝鳍幼鱼的影响。采用生态毒理学方法对体重为7.4±0.6 g的幼鱼进行96小时半数致死浓度（LC50-96h）和氨氮安全浓度的评估。研究设计包括暴露于 LC50-96 小时氨氮水平的应激组和未暴露于氨氮的对照组。为了检查氨氮对鳃组织的生理、生化和代谢影响，在胁迫12、24、48和96小时后收集鳃组织样本，并在48小时后恢复处理。与对照组相比，氨氮对四指丝鳍幼鱼产生不利影响，LC50-96h和安全浓度值分别为20.70 mg/L和2.07 mg/L。暴露于氨氮会导致鳃严重损伤，包括薄片融合、上皮细胞损失和氯分泌细胞增殖。即使在 48 小时的恢复期后，这种组织损伤仍然持续存在。氨氮胁迫引发了鳃中抗氧化酶活性（超氧化物歧化酶、过氧化氢酶和谷胱甘肽过氧化物酶）和丙二醛水平的增加，表明从 12 小时起就出现了氧化应激。尽管酶活性随着时间的推移而下降，但氧化应激即使在恢复后仍然持续存在，这表明持续需要抗氧化防御。代谢组学分析显示 423 种代谢物在氨氮胁迫下发生显着变化。 L-精氨酸、牛磺酸、20-羟基花生四烯酸、11,12-二羟基-5Z、8Z和14Z二十三烯酸等关键代谢物呈增加趋势；尿苷、腺苷、L-谷胱甘肽和胸苷5'-三磷酸呈下降趋势。 这些变化反映了对压力的代谢适应。在富集代谢途径中，主要的差异途径是膜转运、脂质代谢和氨基酸代谢。 48 小时后，与对照组相比，在 396 种代谢物中观察到显着差异。值得注意的是，L-精氨酸、胆碱和L-组氨酸增加，而亚油酸、腺苷和谷胱甘肽减少。氨基酸和脂质代谢途径是关键受影响途径。在氨氮胁迫下，幼年四指鳅增加了不饱和和饱和脂肪酸的合成，以应对低温并通过消耗亚精胺来增强免疫功能。这种适应有助于清除脂肪酸合成过程中产生的过氧化物，从而保护细胞免受氧化损伤。这项研究为池塘养殖和耐氨氮鱼类品种的培育提供了见解。