Effects Of Fish Meal Replacement With Extrudedor Common Soybean Meal On The Growth Performance And Gut-barrier Function Of Grouper (Epinephelus Coioides)

The study was conducted to investigate the effects of extruded or common soybean meal(SBM)replacement fish meal(FM)on growth performance and gut-barrier functions of E.coioides,FM in the dietary was replaced with extruded and common SBM with 0(control group),15%(SBM15,ESM15),30%(SBM30,ESM30),45%(SBM45,ESM45),60%(SBM60,ESM60).A total of 540 fish with an average weight of(52.97±0.10)g were randomly divided into 9 groups with 3 replicate tanks at a stock density of 20 fish per tank,and each group of fish was fed one of the same experimental diets to apparent satiation each time during a feeding period of 56 days.The growth performance and body composition were determined,and the effects of physical barrier,chemical barrier,biological barrier and immune barrier of E.coioides by FM replacement with estruded or common SBM were analysised.Appropriate replacing level of extruded or common SBM with FM in the diets of E.coioides,and difference between extruded and common SBM in performance and gut-barrier functions were investigated:(1)Growth performance and body composition: with the increase in the level of FM substitution with extruded or common SBM,final average weight,weight gain rate,specific growth rate,condition factor and whole-body crude lipid content were gradually decreased.Final average weight,weight gain rate and specific growth rate of ESM60 and SBM60 groups were lower than control group(P(27)0.05),feed efficiency of SBM60 group were lower than control group(P(27)0.05),whole-body crude lipid content of ESM45,ESM60 and SBM60 groups were decreased in comparison with control group(P(27)0.05).However,the growth performance and body composition of grouper were not affected by soybean meal type.The maximum level of extruded and common soybean meal replacing fish meal for E.coioides was 45% based on the weight gain rate.(2)Physical barrier: with the increase in the level of FM substitution with extruded or common SBM,muscle thickness in mid and distal intestine,the height of intestinal mucosa fold in distal intestine were gradually decreased.The height of intestinal mucosa fold and muscle thickness in distal intestine of ESM45,ESM60,SBM45 and SBM60 groups were decreased compared to control group(P(27)0.05),muscle thickness in mid intestine of ESM60 and SBM60 groups were decreased in comparison with control group(P(27)0.05).The intestinal morphology of E.coioides was not affected by soybean meal type.With the increase in the level of extruded SBM replacing FM,mucosal goblet cells of quantities in the distal intestine increased and then decreased,the lamina propria widened and accompanied by lymphocyte infiltration,the submucosal matrix was not filled.With the increase in the level of common SBM replacing FM,mucosal goblet cells of quantities in the mid intestine was gradually increased,the nucleus of simple columnar epithelium migrated,the lamina propria widened and accompanied by lymphocyte infiltration,the intestinal mucosal fold in distal intestine became shorter and damaged at the tap,the nucleus of simple columnar epithelium disordered.(3)Chemical barrier: with the increase in the level of FM substitution with extruded or common SBM,low-density lipoprotein cholesterol and triglyceride contents in plasma were gradually reduced,and endothelin-1 and endotoxin content in plasma were gradually increased,trypsin activity in proximal and mid intestine,protease activity in mid and distal intestine were gradually declined.Triglyceride content in plasma of ESM60 and SBM60 groups were significantly reduced compared to control group(P(27)0.05),and endothelin-1 and endotoxin content in plasma were higher than control group(P(27)0.05).Trypsin activity in mid intestine of ESM60 group,protease activity in distal intestine of SBM60 group were lower than control group(P(27)0.05).With the increase in the level of extruded SBM replacing FM,trypsin activity in proximal intestine increased and then declined,trypsin activity of common SBM substitution groups were lower than control group(P(27)0.05),protease activity in distal intestine declined.Plasma biochemical indexes and intestinal mucosal permeability were not affected by soybean meal type,while trypsin and protease activities were affected by soybean meal type.(4)Biological barrier: there were no significant differences in alpha diversity index about OTU number,Chao1,Ace,Shannon and Simpson compared to control group(P(29)0.05).The diversity of microflora in the distal intestine of E.coioides had no significant difference by substitution FM with extruded or common SBM.With the increase in level FM of substitution with extruded SBM,the Geobacter,Lactobacillus of abandance were no significant difference.With the increase in the level of FM substitution with common SBM,the Geobacter,Lactobacillus of abandance gradually decreased,the vibrio of quantities of ESM60 and common soybean meal substitute groups appeared an increasing trend,but there was no significant difference(P(29)0.05).(5)Immune barrier: with the increase in the level of FM substitution with extruded or common SBM,immunoglobulin M and complement 3 contents in plasma were increased and then decreased,expression levels of IL-10 and TGF-?1 mRAN were gradually reduced,expression levels of IL-8,IL-1?,TNF-? and IL-12 mRNA were gradually increased.Immunoglobulin M and complement 3 contents in plasma of ESM15 and SBM15 groups were higher than control group(P(27)0.05),while the contents of SBM45 and SBM60 groups were lower than control group(P(27)0.05).Expression level of IL-10 mRAN in proximal and mid intestine,expression level of IL-10 mRAN in distal intestine of extruded SBM substitution groups,expression level of TGF-?1 mRNA in mid intestine of common SBM substitution groups were increased and then decreased.Expression level of TGF-?1 mRNA in mid intestine of extruded SBM substitution groups,expression level of TGF-?1 mRNA in distal intestine,expression level of IL-10 mRAN in distal intestine of common SBM substitution groups were gradually decreased,expression levels of IL-12?TNF-? mRAN in proximal intestine of ESM60 and SBM60 groups,expression level of IL-1? mRAN in distal intestine of SBM60,expression level of IL-8 mRNA in mid and distal intestine of ESM60 and SBM60 groups were increased compared to control group(P(27)0.05).Plasma immune index was not affected by soybean meal type,but intestinal inflammatory factor were affected by soybean meal type.The above results suggested that extruded or common SBM replacing FM could reduce the growth performance and whole-body lipid deposit,damage intestinal physical barrier,change in intestinal mucosal permeability,reduce the nutritional status of the body and protease activity in distal and mid intestine,and reduce immunity of E.coioides,while trypsin activity in proximal and mid intestine were increased and then declined,however there were no significant differences in intestinal microorganism.The growth performance,body composition,physical barrier,biological barrier of E.coioides were not affected by soybean meal type,but chemical barrier and immune barrier were affected by soybean meal type.