Biofloc aquaculture is emerging fast as a sustainable technology; however, the system faces challenges from ammonia spikes that affect the physiology of the fishes. Besides, the immuno-stimulatory role of the produced floc in encountering the induced stressor is poorly understood. In this context, the study investigates the effect of different carbon to nitrogen (C/N) ratio on the welfare status of Ompok bimaculatus subjected to acute ammonia stress using an integrated biomarker response (IBR) approach. Four treatments with different C/N ratio of 10, 15, 20 & 25 were designated as C/N10, C/N15, C/N20 and C/N25, alongside a control group with a provision for 80–90% daily water exchange. Twenty-day old O. bimaculatus (average weight = 0.082 ± 0.001 g) larvae were uniformly distributed in each tank (25 l) at a stocking density of 160 nos./tank. At the end of 45-days rearing, fishes were exposed to an acute 96-h ammonia challenge, using a calculated LC₅₀ value of 12.19 mg l⁻¹. Pre- and post-exposure, blood indices like RBC, PVC and Hb were found highest in C/N25, while WBC was highest in C/N20. Plasma total protein, albumin and globulin levels were also elevated in C/N20 group, before and after exposure. Immune scores like lysozyme and respiratory burst activity were found highest in C/N20, whereas the control group showed the lowest activity. Stress biomarkers (glucose and cortisol) showed no significant change (p > 0.05) before exposure, however, levels were elevated in all groups with the highest observed in control and lowest in C/N15 and 20. Before exposure, catalase (CAT) activity was highest in C/N20 in all tissues (liver, gut, muscle); whereas, levels decreased compared to control after exposure. Post exposure, superoxide dismutase (SOD) activity was highest in C/N20 in all tissues (p < 0.05). Before and after ammonia exposure, glutathione peroxidase (GPx) activity in liver was highest in C/N20, whereas, its activity in gut was highest in C/N15. IBR analysis reveals higher values in liver and gut for biomarkers like MDA and GPx, while, SOD showed a plausible level in muscle tissue. Semi-quantitative histological analysis of the gill tissue showed a distinctive pathological damage in all the groups, post-exposure, with the control receiving highest level of alterations, however, not significant with C/N 15 & 25. Probability of survival among groups was highest in C/N20. Overall results from this study indicates a varied immune-stimulatory effect of C/N manipulation with C/N20 delivering highest protection to O. bimaculatus fry against acute ammonia challenge. Further, the IBR approach delineates the probable use of the tissue-level biomarkers for ascertaining the welfare status of O. bimaculatus in the biofloc system.

生物絮团水产养殖作为一种可持续技术正在迅速崛起；然而，该系统面临来自影响鱼类生理机能的氨峰值的挑战。此外，产生的絮状物在遇到诱导应激源时的免疫刺激作用知之甚少。在此背景下，该研究使用综合生物标志物反应 (IBR) 方法研究了不同碳氮 (C/N) 比对遭受急性氨胁迫的Ompok bimaculatus福利状况的影响。C/N 比分别为 10、15、20 和 25 的四种处理被指定为 C/N10、C/N15、C/N20 和 C/N25，以及提供 80-90% 每日换水量的对照组. 二十日龄O. bimaculatus（平均重量 = 0.082 ± 0.001 g）幼虫以 160 条/箱的放养密度均匀分布在每个水箱（25 升）中。在 45 天饲养结束时，使用计算的 LC ₅₀值 12.19 mg l ^{-1 将}鱼暴露于急性 96 小时氨气挑战。暴露前后，RBC、PVC 和 Hb 等血液指标在 C/N25 中最高，而 WBC 在 C/N20 中最高。C/N20 组暴露前后血浆总蛋白、白蛋白和球蛋白水平也升高。发现溶菌酶和呼吸爆发活性等免疫评分在 C/N20 中最高，而对照组的活性最低。压力生物标志物（葡萄糖和皮质醇）没有显着变化（p > 0.05)，然而，所有组的水平都升高，在对照组中观察到最高，在 C/N15 和 20 中观察到最低。暴露前，所有组织（肝脏、肠道）中 C/N20 的过氧化氢酶 (CAT) 活性最高， 肌肉）; 然而，与暴露后的对照相比，水平下降。暴露后，所有组织中 C/N20 的超氧化物歧化酶 (SOD) 活性最高 ( p < 0.05)。在氨暴露前后，肝脏中谷胱甘肽过氧化物酶 (GPx) 的活性在 C/N20 中最高，而在肠道中的活性在 C/N15 中最高。IBR 分析显示肝脏和肠道中 MDA 和 GPx 等生物标志物的值更高，而 SOD 在肌肉组织中显示出合理的水平。鳃组织的半定量组织学分析显示，暴露后所有组都有明显的病理损伤，对照组的改变水平最高，但与 C/N 15 和 25 不显着。组间存活概率为C/N20 最高。这项研究的总体结果表明，C/N 操作具有不同的免疫刺激作用，C/N20 可为O. bimaculatus提供最高保护鱼苗对抗急性氨挑战。此外，IBR 方法描绘了可能使用组织水平生物标志物来确定生物絮团系统中O. bimaculatus的福利状态。