| Biolfoc technology(BFT)is an effective technology to solve the environmental constraints and feed resource shortage faced by the development of aquaculture industry.Rhynchocypris lagowskii Dybowski is a kind of omnivorous small and precious economic fish with the characteristics of fine meat,delicious taste,high nutritional value,wide adaptability and strong disease resistance.This experiment was conducted to study the effects of soybean meal replacing fish meal on growth,immunity and intestinal flora of Rhynchocypris lagowskii Dybowski under BFT system.Juvenile Rhynchocypris lagowskii Dybowski with an initial body weight of(6.88 ± 0.02)g were used as the research object.The fish meal protein of 0.0 %(CK),17.0 %(B17),34.0 %(B34),51.0 %(B51)and 68.0 %(B68)was replaced by soybean meal protein in the compound feed.Five isonitrogenous and isolipidic compound feeds were prepared for an 8-week feeding trial.After the feeding trial,physiology,molecular biological and histological techniques were used.The effects of soybean meal replacing fish meal on the growth and muscle nutrients,digestive enzyme activity and protein metabolism,immune indexes and inflammation-related gene expression,antioxidant capacity and related gene expression,intestinal mechanical barrier and intestinal microbiota of Rhynchocypris lagowskii Dybowski under BFT system were analyzed.These results shown:1.Effects of replacing fish meal with soybean meal on growth and muscle nutrient composition of Rhynchocypris lagowskii Dybowski under BFT systemThe FW,WGR,SGR,FCR,PER and muscle crude protein content of fish in B68 group were significantly lower than the control group(P <0.05);the crude protein content in B68 group were significantly lower than the control group(P<0.05).2.Effects of replacing fish meal with soybean meal on digestive enzyme activities and protein metabolism of Rhynchocypris lagowskii Dybowski under BFT systemCompared with the control group,PRS activities in hepatopancreas and DI in B51 and B68 groups and PI and MI in B68 group were significantly decreased(P < 0.05);however,the replacement of fish meal by soybean meal had no significant effect on the AMS and LPS activities in hepatopancreas,PI,MI and DI(P>0.05).GPT and GOT activities in serum of B68 group were significantly higher than control group(P < 0.05);but GPT and GOT activities in hepatopancreas of B68 group were significantly lower than control group(P<0.05).Compared with the control group,the levels of TOR,IGF-1 and S6 K mRNA in hepatopancreas,PI,MI and DI of B68 group were significantly decreased(P<0.05),while the levels of 4E-BP mRNA were significantly increased(P<0.05);the levels of TOR mRNA in DI,IGF-1 in MI and DI,S6 K in hepatopancreas and DI of B51 group were significantly decreased(P<0.05);while the levels of 4E-BP mRNA in DI were significantly increased(P<0.05).3.Effects of replacing fish meal with soybean meal on immune function and inflammation-related gene expression of Rhynchocypris lagowskii Dybowski under BFT systemThe AKP activities of hepatopancreas,PI,MI,spleen and serum in B68 group and DI and kidney in B51 and B68 groups were significantly lower than control group(P<0.05);but ACP activities in hepatopancreas,PI,MI,DI,kidney,spleen and serum were no significant difference with control group(P>0.05);C3 and C4 contents and LSZ activities in serum of B68 group were significantly lower than control group(P<0.05),and Ig M contents in serum of B68 group were significantly higher than control group(P<0.05).Compared with the control group,the levels of NF-κB,IL-1β and IL-8 mRNA in hepatopancreas,PI,MI and DI of B68 group and DI of B51 group were significantly increased(P<0.05);the levels of TGF-β mRNA in hepatopancreas,PI,MI and DI of B68 group and DI of B51 group were significantly decreased(P < 0.05);the levels of TNF-α mRNA in hepatopancreas,PI,MI and DI of B68 group and MI and DI of B51 group were significantly increased(P<0.05).4.Effects of replacing fish meal with soybean meal on antioxidant capacity and related gene expression of Rhynchocypris lagowskii Dybowski under BFT systemThe SOD and CAT activities of hepatopancreas,PI,MI,and kidney in B68 group and DI and spleen in B51 and B68 groups were significantly lower than control group(P<0.05);the GSH-PX activities of hepatopancreas,PI and kidney in B68 group and MI,DI and spleen in B51 and B68 groups were significantly lower than control group(P<0.05);the T-AOC levels of hepatopancreas,PI,MI and spleen in B68 group,DI and kidney in B51 and B68 groups were significantly lower than control group(P<0.05);the MDA contents of hepatopancreas,PI,MI and kidney in B68 group,DI and spleen in B51 and B68 groups were significantly higher than control group(P<0.05).Compared with the control group,the levels of Nrf2,Maf,CAT,HO-1 and GSH-PX mRNA in hepatopancreas,PI,MI and DI of B68 group and DI in B51 group were significantly decreased(P<0.05);the levels of Keap1 mRNA in hepatopancreas,PI,MI and DI of B68 group were significantly increased(P<0.05).5.Effects of replacing fish meal with soybean meal on intestinal mechanical barrier of Rhynchocypris lagowskii Dybowski under BFT systemCompared with the control group,folds heights and muscular layer thickness of PI,MI and DI in B68 group and DI in B51 and B68 groups were significantly decreased(P<0.05);lamina propria width of PI,MI and DI in B68 group and DI in B51 group were significantly increased(P<0.05).In B51 group,the intestinal villi were broken and showed obvious villi atrophy of MI,the lamina propria was separated and showed obvious villi atrophy of DI.In B68 group,the intestinal villi of MI were broken and lamina propria of DI was widened.The ET-1,D-LA and 5-HT contents and DAO activities in serum of B68 group and DAO activity in B51 group were significantly increased(P<0.05).The levels of ZO-1,Occludin-a,Occludin-b,Claudin-2 and Claudin-4 mRNA in intestinal canal of B68 group and DI in B51 group were significantly decreased(P<0.05).6.Effects of replacing fish meal with soybean meal on intestinal microbiota of Rhynchocypris lagowskii Dybowski under BFT systemAlpha diversity analysis showed that the Simpson indexes of B51 group was significantly lower than control group(P<0.05);the Shannon indexes of the B68 group was significantly higher than control group(P<0.05);there was no significant difference in ACE indexes and Chao1 indexes(P>0.05).At the phylum level,the dominant phylum was Proteobacteria,Firmicutes,Bacteroidetes,Actinobacteria and Cyanobacteria.Proteobacteria dominated in the intestinal flora of fish.The abundance of Proteobacteria in B68 group was significantly lower than control group(P <0.05).At the genus level,the top five species with relative abundance were Roseobacter clade CHAB-1-5 lineage,Uncultured-bacterium f Rhodobacteraceae,Aeromonas,Lactococcus and Uncultured Bacterium f Enterobacteriaceae.Gemmobacter and Uncultured Bacterium f Rhizobiales Incertae Sedis were dominant in the intestinal flora of fish.The abundance of Gemmobacter and Uncultured Bacterium f Rhizobiales Incertae Sedis of B68 group were significantly lower than control group(P<0.05).In conclusion,under BFT system,the appropriate replacement of fish meal by soybean meal should be less than 51.0 % in compound feed for juvenile Rhynchocypris lagowskii Dybowski. |
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