饲料补充后生元对氨氮胁迫下石斑鱼的生长性能、免疫应答、肠道形态及肠道微生物的影响

Effects of Dietary Supplementation with Postbiotic on Growth Performance, Immune Response, Intestinal Morphology, and Gut Microbiota of Grouper under Ammonia-Nitrogen Stress

中文关键词: 后生元  珍珠龙胆石斑鱼  氨氮胁迫  非特异性免疫  消化酶  肠道健康

英文关键词: Postbiotics  Epinephelus fuscoguttatus × Epinephelus lanceolatus  Ammonia-Nitrogen stress  Growth performance  Non-specific immunity  Intestinal morphology  Gut microbiota

中文摘要:

      后生元作为一种新兴饲料添加剂,在水产养殖中正受到越来越多的关注。本研究以初始体重为31.30 ± 0.64 g克的珍珠龙胆石斑鱼为研究对象,评估在氨氮胁迫下饲料后生元对石斑鱼免疫和肠道健康影响。在基础饲料中分别添加0、250、750和2000 mL/ton后生元(本试验所用后生元为液体,浓度30%),形成一个N0和三个试验组,按体重2-3%每天投喂两次,为期8周,之后进行氨氮胁迫(5mg/L)试验1周。结果表明,在氨氮胁迫后,N750和N2000试验组存活率、特定增重率和增重率显著高于N0组(P＜0.05),饵料系数显著低于N0组(P＜0.05)。添加后生元的各试验组肝脏SOD、CAT、ACP、AKP和溶菌酶活力均显著高于N0(P＜0.05),MDA含量显著降低(P＜0.05)。添加后生元的各试验组肠道蛋白酶活力显著提升,而脂肪酶活力显著下降(P＜0.05)。与N0相比,补充后生元后显著提升了石斑鱼肠道绒毛长度,且N2000试验组肠道肌层厚度显著高于N0(P＜0.05),各试验组肠道吸收面积均显著高于N0(P＜0.05)。饲料补充后生元改善了石斑鱼肠道菌群构成,提高了肠道菌群中厚壁菌门和拟杆菌门相对丰度,降低变形菌相对丰度。综上,在本实验条件下,饲料添加后生元能显著改善珍珠龙胆石斑鱼生长、消化酶活性、非特异性免疫能力、肠道形态和肠道菌群构成。

英文摘要:

      With the rapid development of high-density intensive aquaculture, increased stocking densities and accelerated accumulation of residual feed and feces have led to excessive ammonia nitrogen accumulation in water bodies. This phenomenon can induce hepatic damage in aquatic species, impair immune enzyme activity, disrupt intestinal morphology and microbiota, and reduce digestive enzyme vitality. As an emerging feed additive, postbiotics are gaining increasing attention in aquaculture. Defined as inactivated microorganisms and/or their components with a well-characterized genetic background (including or excluding metabolites) that confer health benefits to the host, postbiotics have demonstrated multifunctional properties such as immune modulation enhancement, metabolic promotion, intestinal epithelial barrier reinforcement, antioxidant activity, anticancer effects, anti-inflammatory actions, and gut microbiota balance. However, research on whether dietary postbiotic supplementation improves ammonia nitrogen stress resistance in pearl gentian grouper (Epinephelus fuscoguttatus ♀×Epinephelus lanceolatus ♂) remains limited. This study evaluated the effects of dietary postbiotics on growth, immunity, and intestinal health of pearl gentian grouper (initial body weight: 31.30 ± 0.64 g) under ammonia nitrogen stress.Postbiotics (liquid form, 30% concentration) were supplemented into basal diets at 0, 250, 750, and 2,000 mL/ton, forming a control group (N0) and three experimental groups (N250, N750, N2000). A total of 480 fish were randomly allocated into 12 flow-through aquaculture tanks (300 L), with 40 fish per tank. Each experimental diet was randomly assigned to three tanks. Fish were fed twice daily (09:00 and 17:00) at 2% of body weight for 8 weeks. After the feeding trial, 25 fish from each tank were transferred to a 24-hour aerated static water system for a 1-week ammonia nitrogen stress test (5 mg/L).Results showed that post-ammonia stress, survival rate, specific growth rate (SGR), and weight gain rate (WGR) in the N750 and N2000 groups were significantly higher than those in N0 (P < 0.05), while feed conversion ratio (FCR) was significantly lower (P < 0.05). Postbiotic-supplemented groups exhibited significantly elevated hepatic activities of superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), alkaline phosphatase (AKP), and lysozyme (LZM) compared to N0 (P < 0.05), alongside significantly reduced malondialdehyde (MDA) content (P < 0.05). Intestinal protease activity markedly increased in postbiotic groups, whereas lipase activity decreased significantly (P < 0.05). Compared to N0, postbiotic supplementation significantly enhanced intestinal villus length, with the N2000 group showing notably thicker intestinal muscularis (P < 0.05). All experimental groups displayed significantly increased intestinal villus absorption area relative to N0 (P < 0.05). Dietary postbiotics modulated gut microbiota composition by elevating the relative abundance of Firmicutes and Bacteroidetes while reducing Proteobacteria, thereby improving microbial functionality.Correlation analysis revealed that genera such as unidentified_Kapabacteriales and Methanolinea in the N750 group played positive regulatory roles in immune responses. However, in the high-dose group (N2000), although beneficial Bacillus abundance was maintained, a rebound of Vibrio (similar to N0 levels) and reduced phosphatase-related microbial communities (e.g., Erysipelotrichaceae_UCG-003) suggested potential disruption of microbial homeostasis due to excessive postbiotic supplementation.In conclusion, dietary postbiotics significantly enhanced growth performance, digestive enzyme activity, non-specific immunity, intestinal morphology, and microbiota composition in pearl gentian grouper, improving ammonia nitrogen stress resistance. This study provides theoretical insights into postbiotic-mediated mitigation of ammonia stress in grouper aquaculture, analyzing the impacts of ammonia exposure on fish growth, non-specific immunity, intestinal structure, and microbial ecology. By evaluating the role of postbiotics in enhancing stress tolerance, these findings offer critical data and foundational knowledge for advancing sustainable aquaculture practices and optimizing eco-friendly feed formulations for pearl gentian grouper.