Effects Of Replacing Fish Meal With Plant Protein On Spiral Valve Intestine And Enterohepatic Bile Acid Cycle In Amur Sturgeon(Acipenser Schrenckii)

Plant protein?PP?has become the focus of research on alternative protein sources with increasing shortage of fishmeal production.Amur sturgeon is the oldest cartilaginous scalefish with important biological value,and it is also an important economic fish in China,but there is currently no feed product for Amur sturgeon.The effects of PP on the growth performance,intestinal and liver health of Amur sturgeon are rarely reported.Therefore,this article systematically reported the effects of plant protein feeds on growth performance,spiral valve intestine?SVI?and enterohepatic bile acid?BA?circulation in Amur sturgeon.Three isonitrogenous and isoenergetic diets were prepared.A basal diet containing 540 g/kg fishmeal?P0?,whereas the other two diets were formulated by replacing 50% and 100% of FM with PP blend?soybean protein concentrate and cottonseed protein concentrate?,and named as P50 and P100,respectively.Experimental with an initial weight is 87.48 ± 0.02 g were randomly selected for transfer to 12 conical fiberglass tanks in a recirculation system,with 20 fish per tank,all tanks were arranged for 8 weeks growth trial.Although essential amino acids,fatty acids,and effective phosphorus had been balanced according to the nutrient requirement of sturgeon,the full PP diet significantly reduced Amur sturgeon survival rate?SR?,weight gain rate?WGR?,and protein deposition rate?PPV??P < 0.05?,and accompanied serious spiral valve intestinal?SVI?oxidative damage.We found that SVI microbial diversity significantly decreased?P < 0.05?,potential pathogen genus Clostridium_sensu_stricto₁ significantly increased?P < 0.05?,and genus Turicibacter,a probiotic associated with bile acid reabsorption,was significantly reduced?P < 0.05?in P50 and P100 groups.The strong pathogen Plesiomonas_shigelloides in the genus Plesiomonas was significantly increased in the P100 group?P < 0.05?.With the significant increase of SVI reactive oxygen species?ROS?in P100 group?P < 0.05?,mucosal barrier and tight junction?Occludin and ZOs?were broken,and height of mucosal folds were shortened in damaged SVI.The full PP diet suppressed SVI anti-oxidation?Keap1,Cu / Zn-SOD,CAT,GST1 and GST3?,autophagy?ATG7,ATG16 and LCB-II / I?,proliferation?CyclinD1 and CyclinE?,programmed apoptosis?caspase3,caspase8 and caspase9?,immune cytokines?IL-1?,IL10 and serum IgG?and ERK1 phosphorylation?P < 0.05?.The results showed that failed responses in anti-oxidation,apoptosis,autophagy and cell proliferation system were regulated by inhibiting ERK1 phosphorylation,which indicated that SVI hypoimmunity and functional degradation were the main reasons for the high mortality and low utilization ability of plant protein in Amur sturgeon.Changes in intestinal microbiota and SVI lesion induced BA reabsorption disorder,SVI BA content significantly decreased and SVI BA receptors?nuclear receptor FXR and membrane receptor TGR5?down-regulated in P100 group?P < 0.05?.Hepatic cholesterol synthesis key enzyme HMGCR was significantly up-regulated?P < 0.05?in P100 group,while cholesterol content was not significantly different in each group?P > 0.05?.The nuclear receptor FXR was significantly down-regulated?P < 0.05?,and BA synthesis key enzymes CYP7A1 and CYP8B1 were significantly up-regulated?P < 0.05?,and hepatic BA was significantly increased?P < 0.05?in P100 group.Accumulation of bile acids induced a significant increase in hepatic ROS?P < 0.05?,immune cytokines?TGF?1and IL10?and programmed apoptosis?caspase9 and caspase3?were suppressed?P < 0.05?.With the increase of hepatic BA and lipid in P100 group?P < 0.05?,fatty liver and fibrotic lesions increased.The results showed that with increasing dietary plant protein,disruption of SVI microbiota and more fatty liver and hepatic fibrosis were observed in full PP diet group.Increased liver BAs compensatory synthesis induced by BA enterohepatic circulation disorder,which further induced oxidative stress and hypoimmunity and hepatic lesion were non-negligible reasons for the high mortality and low utilization ability of plant protein in Amur sturgeon.