Studies On Utilization Of Dietary Carbohydrate For Cobia(Rachycentron Canadum L.) And Effects Of Probiotics And Inulin On Intestinal Microbiota In Golden Pompano(Trachinotus Ovatus)

This article investigated the effects of dietary carbohydrate levels on the growth performance and intestinal microbiota of cobia（Rachycentron canadum）and dietary supplementation with Lactobacillus reuteri,Bacillus amyloliquefaciens,Bacillus coagulans and inulin on the growth performance and intestinal microbiota of golden pompano（Trachinotus ovatus）to provide a reference for evaluating the effects of diets with carbohydrate for cobia,probiotics and inulin as feed additives for golden pompano.The conclusions are as follows:1 In the present study,four isonitrogenous and isolipidic diets were prepared to investigate the effects of dietary Carbohydrate（CBH）level（4.8-22.5%）on growth performance,feed utilization,body composition,and intestinal microbiota of juvenile cobia(initially weighing 22.2±0.27 g·fish^-1).Each diet was given to triplicate groups of cobia for 8 weeks.Both the final body weight and specific growth rate increased with increasing dietary CBH levels.Feed intake decreased with increasing dietary CBH levels（P<0.05）,whereas feed efficiency and the protein efficiency ratio increased（P<0.05）.As the level of dietary CBH increased,linear responses were observed for the condition factor,hepatosomatic index,viscerosomatic index,and intraperitoneal fat ratio（P<0.05）.The whole-body lipid content generally increased with increasing dietary CBH levels,with the lipid content of fish fed a 22.5%dietary CBH diet being significantly higher than other treatments.Moisture content showed the reverse response to that of lipids.Body protein and ash contents were not significantly related to dietary CBH（P>0.05）.Activities of hepatic glucokinase linearly increased with increasing dietary CBH levels,being significantly higher in fish fed a 22.5%CBH diet compared with other groups（P<0.05）.In contrast,the activities of hepatic hexokinase and pyruvate kinase showed the opposite trend.The activities of intestinal amylase and trypsin were negatively related to dietary CBH levels.Thus,dietary CBH promoted the growth and feed utilization of cobia,although it also had negative effects,such as higher lipid deposition and higher body indices.Based on 16S r RNA gene sequencing,at the phylum level,Proteobacteria,Bacteroidetes and Achromobacter were the predominant phylum;at the genus level,the dominant bacteria included Pandoraea,Bacteroides,Achromobacter and Lactobacillus.The abundance of Pandoraea and Lactobacillus increased significantly with the increase in dietary carbohydrate content.In conclusion,we recommend that the dietary CBH level for juvenile cobia should not exceed 22.5%.2 Probiotics not only could sustain intestinal health by modulating intestinal microbiota and improving the gut barrier but also increased growth performance,which presented a high potential for aquaculture.This experiment was conducted to investigate the effects of dietary supplementation with Lactobacillus reuteri,Bacillus amyloliquefaciens and Bacillus coagulans on the growth performance and intestinal microbiota of golden pompano.In terms of probiotics,we produced six isonitrogenous and isolipid diets,including L1 for the control group with 17.74%carbohydrate level,L2 for the 22.14%carbohydrate level group,L3 with L.reuteri(0.1 g·kg^-1),L4 with B.amyloliquefaciens(0.1 g·kg^-1),L5 with B.coagulans(0.5g·kg^-1),and L6 for the experimental group with equal proportions of the three probiotics.Three replicates of 30 fish per replicate were fed to golden pompano（initial weight 13.46±0.02 g）with their diet for 8 weeks.Results showed that the final body weight（FBW）,weight gain（WG）and specific growth rate（SGR）of golden pompano in L3 and L4 groups were significantly increased compared with the L1 and L2 groups（P<0.05）.The intestinal enzymes activities in the L3 and L5groups were significantly lower than those in the L2 and L6 groups,whereas the intestinal chymotrypsin activities in the L3,L4 and L5 groups were significantly higher than those in the L1 and L6 groups（P<0.05）.The cholesterol（CHO）,triglyceride（TG）and high-density lipoprotein（LDL）levels in the L4,L5 and L6groups were significantly higher than those in the L2 group（P<0.05）.At the phylum level of the intestinal microbiota,the abundance of Proteobacteria in the L3 group was lower than the L1 and L2 groups,while the opposite trend was observed for the Firmicutes and Bacteroidetes.At the genus level,the abundance of Achromobacter,Delftia and Brevundimonas in the L3,L4 and L5 groups were lower than those in the L2 group,while the minimum value was obtained in the L3 group（P>0.05）.However,the abundance of Prevotella 9 in the L3 group was significantly higher than that in the other groups（P<0.05）.Taken together,we found that L.reuteri and B.amyloliquefaciens as feed additives improved the growth performance of golden pompano,and the L3 group showed the best results.3 Prebiotics,such as inulin,can beneficially affect the host by selectively stimulating the growth and/or activating the metabolism of health-promoting bacteria in the intestinal tract.A 8-week feeding experiment was conducted to investigate the effects of dietary inulin on survival,growth performance,body indices,and intestinal microbiota of juvenile golden pompano（initial average weight 18.85±0.02 g）.Six isonitrogenous and isolipidic basal diets were supplemented with 0（control）,0.3%,0.6%,0.9%,1.2%,and 1.5%inulin.Each diet was fed to triplicate groups of fish（30fish per group）.Fish were fed to apparent satiation twice a day,and growth performance was monitored.Results showed that the fish fed the inulin diets exhibited better performance than fish fed the control diet,with fish fed diet supplemented with 1.5%inulin had the highest survival rate among all diets tested,significantly higher than the other groups（P<0.05）,and no significant difference was found among the other groups（P>0.05）.The final body weight,weight gain,and specific growth rate were highest in fish of 1.5%-inulin supplementation dietary group.The hepatosomatic index and intraperitoneal fat were significantly lower in inulin included groups.The hepatosomatic index were decreased with increasing levels of dietary inulin,with the lowest value observed in 0.9%inulin supplementation dietary group,and the increased.Fish fed diets containing 1.2%and 1.5%inulin had the lowest values of intraperitoneal fat,significantly lower than fish in the other groups.Fish fed inulin included diets had higher gut villus height than that of fish in control group.The Proteobacteria,Firmicutes,and Bacteroidetes were the predominant species of intestinal microbiota communities.Their abundances varied among dietary groups.The highest and lowest abundances of Proteobacteria were appeared in 1.5%and 1.6%-inulin inclusion groups,respectively.Fish fed diets supplemented with0.6%-inulin had the highest abundances of Firmicutes and Bacteroidetes.The lowest abundances of Firmicutes and Bacteroidetes were found in fish of 1.5%-inulin supplementation group and control group,respectively.The predominant species at genus level were Achromobacter,Brevundimonas,and Pandoraea.Achromobacter was most abundant in 1.5%-inulin supplementation group.Fish of 1.5%-inulin supplementation group had the lowest abundances of Achromobacter,Brevundimonas,Pandoraea,Delftia,and Sphingomonas.Inulin supplementation increased the abundances of bacteria that are beneficial to the host such as Achromobacter and Prevotella.These findings indicate that inulin has great potential for use as prebiotics in the feed of juvenile golden pompano.Dietary supplementation of Inulin at 1.5%can enhance the survival and growth performance of juvenile golden pompano.