Study On Apparent Digestibility Coefficients Of Different Protein Sources,and Hydroxyproline Supplementation With Partial Replacement Of Fish Meal With Fermented Soybean Meal In Feed Of Chinese Perch(Siniperca Chuatsi)

Taking Chinese perch(Siniperca chuatsi)as the research object,this study explored the apparent digestibility coefficients(ADCs)of different protein sources in feed and the hydroxyproline supplementation with partial replacement of fish meal with fermented soybean meal.The main results are as follows:1.Study on apparent digestibility coefficients of different protein sources.In previous studies of ADCs,the association between apparent digestion and protein metabolism from different protein sources has long been ignored.To develop nutritionally adequate diets,this study evaluated the effects of different protein sources[fermented soybean meal(FSM),rapeseed meal(RSM),Antarctic krill powder(AKP)and fish protein hydrolysate(FPH)] on the growth performance,ADCs and expression of genes related to protein metabolism in Chinese perch.The experimental feed was composed of 30% test ingredients and 70% reference feed(RF).After the feeding trial,FPH was found to achieve the best growth performance of Chinese perch,and had significantly higher ADCs of dry matter and gross energy than all other ingredients.Besides,FPH was the only ingredient with crude protein ADC exceeding 90% and the highest crude lipid ADC,while RSM had the lowest crude protein and crude lipid ADC.FPH showed the highest ADC of amino acids except for serine and tyrosine,and RSM showed the lowest amino acid ADC except for methionine.FPH resulted in the lowest expression of mtor,s6 k,murf1,mafbx,pept2 and lat2,and the highest expression of gdh and ast in the muscle.The transcription level of cat2 significantly increased in the gut of the FSM group compared with that in the RF group.These findings imply that FPH may be a promising ingredient to be incorporated into the formulated diet of Chinese perch.2.Study on hydroxyproline supplementation with partially replacement of fish meal with fermented soybean meal.As a kind of biologically active molecule,hydroxyproline(Hyp)is abundant in fish meal(FM)but not in plant protein sources.It remains very challenging to replace FM with plant protein sources,particularly for carnivorous fish.This study aims to investigate the effect of dietary Hyp supplementation on Chinese perch fed with FM partially replaced by fermented soybean meal(FSM),with 46% FM as the positive control and 31%FM plus 15% FSM as the negative control.Based on the negative control diet,0.5%,1%,1.5% and 2% of dietary crystal L-Hyp was supplemented to formulate four experimental diets,respectively.Although the replacement of 15% FM with FSM in the feed resulted in a significant decline in growth performance of Chinese perch,dietary supplementation of 1% Hyp could improve the growth performance with high m RNA levels of the gh and igf1 genes.Piecewise regression analysis revealed that a dietary level of 2.27% Hyp could achieve the maximum weight gain rate.With high m RNA levels of orexigenic genes(npy and agrp in the brain,and ghrelin in the gut)and low m RNA levels of anorexigenic genes(pomc and cart in the brain,and leptin-A in the liver),an appropriate level of Hyp could be added to the diet of Chinese perch as a food attractant to promote the appetite and increase food intake.Besides,partial replacement of FM with FSM might promote the deposition of amino acids in the muscle,which may not be affected by dietary supplementation of Hyp.Furthermore,dietary supplementation of Hyp affected the activity of prolyl hydroxylase(PHD)and the m RNA levels of type Ⅰ collagen regulatory genes and coding genes of three prolyl 4-hydroxylase(P4H)isozymes in the muscle of Chinese perch to some extent.In addition,supplementation of an appropriate level of Hyp could significantly improve the collagen content and muscle quality(hardness,chewiness and springiness)of Chinese perch,which may greatly enhance its edible and nutritional values.