饲料糖脂比对吉富罗非鱼生长、生理生化指标、肠道菌群组成及抗病力的影响

为研究不同糖脂比饲料对罗非鱼幼鱼生长、生理生化指标、肠道菌群组成和抗病力的影响。实验选取平均体重为27g的罗非鱼幼鱼为研究对象，分别用等氮等能的五种不同糖脂比饲料: 44.2/4(D1)、39.6/6(D2)、35/8(D3)、30.4/10(D4)、25.6/12(D5)，饲喂10周，采用营养学、生化分析结合高通量测序技术开展了相关测定研究。结果显示，糖脂比饲喂前期对罗非鱼生长具有显著影响，高糖或高脂饲料均生长较差，但饲喂到10周后，所有组间生长无显著差异 (P > 0.05)。相比之下，10周糖脂比在脏体比、肠系膜脂肪指数、肝体比、全鱼粗蛋白、肝脏甘油三酯、血清低密度脂蛋白胆固醇（LDL）和尿素、抗病力、菌群组成等方面存在显著效应。低糖脂比D4在脏体比上显著高于高糖脂比D1 (P < 0.05)，而在血清尿素和抗病力上显著低于D1 (P < 0.05)，在肠系膜指数上显著高于高糖脂比D1和D2 (P < 0.05)，但在全鱼粗蛋白上显著低于D1和D2 (P < 0.05)。另外，D1不仅在肝体比上高于低糖脂比D5 (P < 0.05)，而且在LDL和糖耐受能力上均高于其它各组 (P < 0.05)。与之相比，糖脂比虽在肠道微生物物种丰度和均一度上没有显著性差异 (P < 0.05)，但在物种组成和热图显示低糖脂比D4与其它组肠道菌群组成不同。D4在聚类关系上单独一支，其门水平上衣原体门、绿弯菌门、放线菌门高于其它各组，特别是D2和D1，但厚壁菌门低于其它各组，特别是D2; 属水平上，D4组幽门螺杆菌属明显多于其它组，而乳杆菌、双歧杆菌属明显少于除D3外的其它组。综上所述，罗非鱼对不同糖脂比饲料有很强的适应和利用能力，但高糖比饲料利用上强于低糖脂比。本实验条件下，高糖组中39.6/6(D2)饲料组虽然在生长上与其它各组无显著差异，但其鱼体粗蛋白含量在各组中最高，肠道菌群组成上也优于其它各组，是罗非鱼适宜的糖脂比水平。

Effects of dietary carbohydrate-to-lipid ratio on growth, physiology and biochemistry, gut microbiota and disease resistance of GIFT tilapia (Oreochromis niloticus)

The experiment was conducted to study the effects of different carbohydrate to lipid ratio diets on growth, physiological and biochemical indices, gut microbiota composition and disease resistance of juvenile tilapia (Oreochromis niloticus). Fish with an average body weight of 27g were selected as the research object. Five isonitrogenous and isoenergetic diets with different carbohydrate-to-lipid ratios were used respectively: 44.2/4(D1), 39.6/6(D2), 35/8(D3), 30.4/10(D4), 25.6/12(D5) and fed for 10 weeks. Nutritional and biochemical analysis methods combined with high-throughput sequencing technology were used to determine the indices. The results showed that the changed C/L ratio had significant effect on the growth of tilapia in the early feeding stage, and the growth effect of low- C/L ratio was better than the high- C/L ratio. While after 10 weeks, there was no significant difference among all groups (P > 0.05). In addition, C/L ratios had significant effects on viscera/body ratio, mesenteric fat index, hepatosomatic ratio, whole fish crude protein, liver triglyceride, serum low density lipoprotein cholesterol and urea, and disease resistance. Specifically, low C/L ratio-D4 was significantly higher than high C/L ratio-D1 in viscera/body ratio (P < 0.05), while whose serum urea and disease resistance were lower than D1 (P < 0.05). Moreover, mesenteric index of D4 was higher than high C/L ratios D1 and D2 (P < 0.05), while whose whole-body crude protein was significantly lower than D1 and D2 (P < 0.05). On the other side, the hepatosomatic of D1 was higher than that of low C/L ratio-D5 (P < 0.05), and the low-density lipoprotein cholesterol and glucose tolerance of D1 were higher than those of other groups (P < 0.05). The species composition and heat map showed that D4 was separated from the other groups. In terms of phylum heatmap, chlamydia, chloroflexi and actinomycetes of D4 were higher than other groups (especially D2 and D1), while its firmicutes were lower than other groups (especially D2). Further in genus level, phreatobacter of D4 was significantly higher than that of other groups, while lactobacillus and bifidobacterium in D4 was significantly lower than that of other groups (except D3). In conclusion, tilapia has strong adaptability and utilization ability to different C/L ratio diets, and the utilization of high C/L diets is stronger than that of low C/L diets. Under the experimental conditions, although 39.6/6(D2) diet group had no significant difference with other groups in growth, its whole-body crude protein content was the highest among groups, and the composition of gut microbiota was also superior to other groups, which was an appropriate C/L level for tilapia.