发酵豆粕替代鱼粉对大口黑鲈幼鱼生长、脂质代谢、血清非特异性免疫及肠道菌群的影响

为探讨发酵豆粕替代鱼粉对大口黑鲈(Micropterus salmoides)幼鱼生长、脂质代谢、血清非特异性免疫及肠道菌群的影响, 试验在基础饲料中用发酵豆粕分别替代0、10%、20%、30%和40%鱼粉, 用晶体氨基酸平衡各组间蛋氨酸与赖氨酸的差异, 配制成共5种等氮等能(CP47%, GE19 MJ/kg)的试验饲料, 分别为FM、FSM10、FSM20、FSM30和FSM40。将初始体重为(22.05±0.09) g的大口黑鲈随机分成5组, 每组设3个重复, 养殖58d。生长试验结果表明: 各组之间增重率(WGR)、特定生长率(SGR)、肥满度(CF)、肝体比(HSI)和脏体比(VSI)均无显著差异(P>0.05), 但替代组饲料系数(FCR)均显著高于FM对照组(P<0.05), FSM40组的存活率(SR)和干物质表观消化率(ADDM)显著低于其余各组(P<0.05)。脂质代谢方面结果显示, FSM30和FSM40组的血清甘油三酯(TG)水平显著低于FM对照组(P<0.05), FSM40组的血清总胆固醇(T-CHO)水平显著低于FM对照组(P<0.05)。血清非特异性免疫方面结果表明, FSM40组的溶菌酶(LZM)和超氧化物歧化酶(SOD)活性有显著增加的变化(P<0.05)。对肠道菌群进行了Illumina Mi Seq高通量测序分析, 结果表明: 各组肠道菌群的Alpha多样性指数(Sobs、Shannon、Simpson、Ace和Chao)无显著差异(P>0.05), 但OTU数量发生了变化。在门水平上, 优势菌群为软壁菌门(Tenericutes)、变形菌门(Proteobacteria)和梭杆菌门(Fusobacteria); 而属水平上, 优势菌群为支原菌属(Mycoplama)、邻单胞菌属(Plesiomonas)和鲸杆菌属(Cetobacterium)。FSM20组与FM对照组相比, 软壁菌门和支原菌属的相对丰度显著提高(P<0.05), 变形菌门和邻单胞菌属的相对丰度显著降低(P<0.05)。综上所述, 在试验条件下, 大口黑鲈饲料中发酵豆粕替代20%鱼粉不会对大口黑鲈幼鱼生长、脂质代谢、血清非特异性免疫及肠道菌群多样性造成负面影响, 且能显著降低肠道中邻单胞菌属在内的有害菌的相对丰度, 因此, 发酵豆粕替代鱼粉的适宜比例为20%。

FERMENTED SOYBEAN MEAL INSTEAD OF FISH MEAL ON GROWTH,LIPID METABOLISM,SERUM NON-SPECIFIC IMMUNITY AND INTESTINAL FLORA OF JUVENILE LARGEMOUTH BASS

The global fishmeal is lacking, and the search for fishmeal substitutes has become a hot issue in the research of aquatic animal nutrition, which is of great practical significance. Soybean meal has a high protein content, a stable and low supply, and is considered as a good fish meal substitute, however, because it contains many anti-nutritional factors, including protease inhibitors, lectins, phytic acid, saponin, phytoestrogens, anti-vitamins and allergens, it will inhibit the digestion and absorption of nutrients to a certain extent. In addition, studies have shown that the replacement of fish meal with soybean meal can induce disorders of the intestinal microbiota of fish, and excessive replacement can also induce adverse reactions such as enteritis, oxidative stress and immune dysfunction in fish. However, soybean meal can reduce most anti-nutritional factors after microbial fermentation, and degrade macromolecular proteins into small peptides and water-soluble compounds, thereby increasing its nutritional value and enhancing the digestibility of nutrients. At the same time, it can also provide animals with probiotics and prebiotics, and can increase the content of free amino acids with antioxidant properties, such as histidine, serine, valine and lysine, and the concentration of phenolic compounds. In this context, the soybean meal was fully fermented under aerobic conditions with Bacillus subtilis as the bacterial source, and the fermented soybean meal used in this study was obtained. This product removed most of the anti-nutritional factors and degraded most of the molecular protein, increased amino acid content, has a good potential to replace fish meal. At present, the research on soybean meal fermented by Bacillus subtilis mainly focuses on the hydrolysis of soybean protein and the improvement of antioxidant activity, and there is very little research on the effect of fish feeding. Largemouth bass (Micropterus salmoides) has been introduced into China since it has been widely cultivated due to its delicious meat, few intermuscular spines, and strong disease resistance. After years of breeding development, it has become one of the important species of freshwater aquaculture in China. Therefore, the largemouth bass was used as the research object, and proved the feasibility of Bacillus subtilis fermented soybean meal to replace fish meal through experimental research, hoping to provide some references for the optimization of largemouth bass feed formula and the sustainable development of artificial breeding industry. To explore the effects of fermentation of soybean meal instead of fish meal on the growth, lipid metabolism, serum non-specific immunity and intestinal flora of juvenile largemouth bass, fish meal was replaced with fermentation of soybean meal at 0, 10%, 20%, 30%, and 40%, respectively. Crystal amino acids were used to balance the difference between methionine and lysine in each group, and 5 isonitrogen equal energy diets (CP47%, GE19 MJ/kg) referred to as FM, FSM10, FSM20, FSM30 and FSM40 were used to feed Largemouth bass with an initial weight of (22.05±0.09) g with three replicates for 58 days. The results showed that there were no significant differences in the weight gain rate (WGR), specific growth rate (SGR), condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) among groups (P>0.05), but soybean meal significantly increased the feed coefficient ratio (FCR) (P<0.05). The survival rate (SR) and apparent dry matter digestibility (ADDM) of the FSM40 group were significantly lower than other groups (P<0.05). The serum triglyceride (TG) levels of the FSM30 and FSM40 groups were significantly lower than the FM control group (P<0.05), and the serum total cholesterol (T-CHO) level of the FSM40 group was significantly lower than the FM control group (P<0.05). The activities of lysozyme (LZM) and superoxide dismutase (SOD) in the FSM40 group increased significantly (P<0.05). The Alpha diversity indexes (Sobs, Shannon, Simpson, Ace and Chao) of of intestinal flora had no significant difference among groups (P>0.05), but the number of OTUs were different. The main phyla in intestine of fish were Tenericutes, Proteobacteria and Fusobacteria in soybean meal groups; the dominant genera were Mycoplama, Plesiomonas and Cetobacterium. Compared with the FM control group, the relative abundances of Tenericutes and Mycoplama in the FSM20 group increased significantly (P<0.05), and the relative abundances of Proteobacteria and Plesiomonas significantly reduced (P<0.05). Overall, under the experimental conditions, the replacement of 20% fish meal with fermented soybean meal in largemouth bass feed did not have a negative impact on the growth, lipid metabolism, serum non-specific immunity and intestinal flora diversity of largemouth bass juveniles, and It significantly reduced the relative abundance of harmful bacteria including the Plesiomonas in intestine, so the appropriate ratio of fermented soybean meal to replace fish meal was 20%.