Heat-killed probiotics offer an alternative approach to enhance growth and disease resistance in farmed fish. In this study, we isolated Lactiplantibacillus plantarum VSG3 from the gut of Labeo rohita to investigate the effects of heat-killed L. plantarum (HK-LP) on the health and growth performance of Cyprinus carpio fingerlings. Different concentrations of HK-LP (0, 50, 100, 200, 300, and 400 mg/kg) were administered to the fish, followed by a challenge with Aeromonas hydrophila after 8 weeks of feeding. Notably, the LP200 group exhibited significantly improved percentage weight gain and specific growth rate, accompanied by the lowest feed conversion ratio. Post-challenge survival rates were considerably enhanced in the LP200 group, reaching 60.65%. Moreover, serum analysis indicated significantly higher levels of total protein and albumin in the LP200 group than in the control group. Although HK-LP had no substantial impact on certain serum parameters (glucose, total cholesterol, cortisol, and alanine aminotransferase), aspartate aminotransferase levels were considerably low in the LP200 group. Intestinal protease and trypsin activities significantly increased in the LP200 group, while no significant changes were observed in lipase and amylase activities post-pathogen challenge. Serum immunological indices, including lysozyme, alternative complement pathway, and phagocytic activity, improved considerably in the LP200 group. Additionally, serum antioxidant enzyme activities (superoxide dismutase [SOD], glutathione peroxidase [GPx], catalase [CAT], and myeloperoxidase) were significantly elevated in the LP200 group, while malondialdehyde level was reduced. Gene expression analysis in liver tissue indicated strong upregulation of antioxidant-related genes (SOD, CAT, nuclear factor erythroid 2 [NFE2]-related factor 2 [Nrf2], Kelch-like ECH-associated protein 1[Keap1]) in the LP100 and LP200 groups. Pro-inflammatory cytokines (IL-1β and TNF-α) were considerably downregulated in the kidneys of the LP200 post-challenged fish, although the anti-inflammatory cytokine IL-10 showed an increased expression. Quadratic regression analysis identified the optimal dietary HK-LP level for maximizing growth and immune performance (200.381–270.003 mg/kg). In summary, our findings underscore the potential of HK-LP as a valuable dietary supplement for enhancing carp aquaculture, particularly at the appropriate concentration.

热灭活益生菌提供了一种增强养殖鱼类生长和抗病能力的替代方法。在本研究中，我们从Labeo rohita肠道中分离出植物乳杆菌VSG3，以研究热灭活乳杆菌的作用。plantarum (HK-LP) 对鲤鱼鱼种健康和生长性能的影响。给鱼施用不同浓度的HK-LP（0、50、100、200、300和400毫克/千克），然后在喂食8周后用嗜水气单胞菌进行攻击。值得注意的是，LP200 组的增重百分比和特定生长率显着提高，同时饲料转化率最低。 LP200 组的攻击后存活率显着提高，达到 60.65%。此外，血清分析表明LP200组的总蛋白和白蛋白水平显着高于对照组。尽管 HK-LP 对某些血清参数（葡萄糖、总胆固醇、皮质醇和丙氨酸转氨酶）没有实质性影响，但 LP200 组的天冬氨酸转氨酶水平相当低。 LP200组的肠道蛋白酶和胰蛋白酶活性显着增加，而病原体攻击后脂肪酶和淀粉酶活性没有观察到显着变化。 LP200组的血清免疫学指标，包括溶菌酶、替代补体途径和吞噬活性显着改善。此外，LP200组的血清抗氧化酶活性（超氧化物歧化酶[SOD]、谷胱甘肽过氧化物酶[GPx]、过氧化氢酶[CAT]和髓过氧化物酶）显着升高，而丙二醛水平降低。肝组织中的基因表达分析表明 LP100 和LP200组。 LP200 攻击后鱼的肾脏中促炎细胞因子（IL-1β 和 TNF-α）显着下调，但抗炎细胞因子 IL-10 显示表达增加。二次回归分析确定了最大化生长和免疫性能的最佳膳食 HK-LP 水平 (200.381–270.003 mg/kg)。总之，我们的研究结果强调了 HK-LP 作为一种有价值的膳食补充剂来促进鲤鱼水产养殖的潜力，特别是在适当的浓度下。