| In recent years,the artificial breeding of Nibea albiflora has developed rapidly in the southeast coastal areas of China,and the demand for high quality artificial compound feed is also increasing gradually.Fish meal is the most commonly used protein source in aquatic feed.Due to the decline of global fishery resources,the annual production of fish meal has decreased and the price has increased sharply.Therefore,it has become a hot issue in the aquaculture industry to find high-quality and inexpensive protein source to replace fish meal..In this paper,juvenile N.albiflora was taken as the research object,and the nutritional requirements of juvenile N.albiflora were studied from the three aspects of the optimal protein source,the optimal substitution level of cottonseed meal and Poultry by-products meal.The results can not only provide a useful reference for improving the utilization of plant and animal protein sources of juvenile N.albiflora,but also provide important basic information for the nutrition research of N.albiflora.1.Study on screening of suitable protein sources for juvenile Nibea albifloraAn 8-week feeding trial was conducted to evaluate the effects of different protein sources on the growth performance,feed utilization,body composition and muscle amino acids contents of juvenile N.albiflora.Eight different protein source diets were formulated,which consisted of 70% of the basic feed and 30% of the test protein sources.The dietary protein sources were fish meal(control group),cottonseed meal,soy protein concentrate(SPC),peanut meal,rapeseed meal,black soldier fly,poultry by-products and spray-dried blood cell,respectively.For the feeding trial,480 juvenile N.albiflora with initial weight(9.00±0.05)g were transferred into 24 cylindrical fiberglass tanks,with 20 fish per tank.The results indicated that the weight gain rate,specific growth rate,survival rate and feed utilization of fish fed the cottonseed meal,and SPC diets were the highest except for the control group(P < 0.05);While the spray-dried blood cell group was significantly lower than that of fish fed the control group(P < 0.05).The whole body crude protein and lipid content,and muscle crude lipid content of fish fed the spray-dried blood cell diet was significantly lower than those of fish on the other diets and the control diet(P < 0.05);The muscle crude lipid content of poultry by-products group was the highest,and significantly higher than those of fish fed the rapeseed meal and spray-dried blood cell diet(P < 0.05);The types of amino acids in the muscles of juvenile N.albiflora in diets are the same,but the amino acid contents of fish fed different diets are significantly different(P < 0.05).The muscle total amino acids contents in N.albiflora fed all diets are more than 93%,and the total amount of essential amino acids are more than 45%.In conclusion,this study indicated that poultry by-products,SPC,cottonseed meal and peanut meal are the better source of protein in the compound feed of juvenile N.albiflora,which can be further developed for the appropriate replacement of fish meal protein source.2.Study on suitable proportion of cottonseed meal replacement of fishmeal in diet of juvenile Nibea albiflora.Based on the results of Experiment 1,we selected cottonseed meal as the best plant protein source representative of juvenile N.albiflora,and further carried out the study on the appropriate proportion of cottonseed meal to replace fish meal in the feed of juvenile N.albiflora.six isoenergetic and isolipidic diets were produced,use cottonseed meal to replace0%(CM0),12%(CM12),24%(CM24),36%(CM36),48%(CM48),60%(CM60)of fish meal protein.For the feeding trial,360 juvenile N.albiflora with initial weight(8.68±0.05g)were transferred into 18 cylindrical fiberglass tanks,with 20 fish per tank,the trial was carried out for 8 weeks in an indoor culture system.Results shows that the weight gain rate(WGR)and specific growth rate(SGR)decreased significantly when the cotton meal replacement level reached 60%(P < 0.05);The FCR significantly decreased with increasing dietary cottoned meal levels(P < 0.05).There was no significant difference in the content of water,crude protein,crude lipid and ash in the whole body of fish among all treatments(P >0.05).The high replacement ratio of cotton meal has a destructive effect on the intestinal tissue structure.The structure of the intestine of fish on CM60 diet was severely damaged,the arrangement of cells was sparse,the boundary was fuzzy,the nucleolus was shrunk,and the lymphocytes were infiltrated.Relative expression of intestine IGF-1and IGFBP2 of fish on CM 60 diet significantly lower than those of fish on CM48 diet(P < 0.05);However,the IGF1 R expression of fish on CM0 diet was the higher than CM48 and CM60 diets.The expression of Claudin,JAM1 and ZO1 in the CM60 diet were significantly lower than those in the CM0 and CM48 diets(P < 0.05),but the expression levels of Occlaudin and MUC2 in the CM0 diet were significantly higher than those of the other two diets(P < 0.05).Based on the broken line model analysis of weight gain rate,under the experimental conditions,the optimal proportion of cottonseed meal in the diet of juvenile N.albiflora is 48.52%.3.Study on suitable proportion of Poultry by-products meal replacement of fishmeal in diet of juvenile Nibea albiflora.Based on the results of Experiment 1,we selected Poultry by-products(PBM)as the representative of the best animal protein source of N.albiflora,and further studied the appropriate proportion of PBM to replace fish meal in the feed of juvenile N.albiflora.six isoenergetic and isolipidic diets were produced,use PBM to replace 0%(CM0),12%(CM12),24%(CM24),36%(CM36),48%(CM48),60%(CM60)of fish meal protein.For the feeding trial,360 juvenile N.albiflora with initial weight(7.00±0.05 g)were transferred into 18 cylindrical fiberglass tanks(500 L),with 20 fish per tank,the trial was carried out for 8 weeks in an indoor culture system.Results shows that the weight gain rate(WGR)and specific growth rate(SGR)were highest when the PBM replacement level reached 24%(P< 0.05);The FI of fish was the lowest in the diet of PM60.There was no significant difference in the Hepatosomatic index(HSI)and Viscera somatic index(VSI)of fish on all diets(P > 0.05).The crude protein content of whole fish was highest in the diet of PM60,the content of water and lipid in whole was not affected by the replacement level of PBM(P > 0.05).There was no significant difference in the content of water,crude protein in the muscle of fish among all treatments(P > 0.05),while the content of crude lipoid decreased with the proportion of PBM,and the lowest was at 60% of PBM.The results of HE staining showed that there was no significant change in the intestinal tissue between PM12 and PM0diets(P > 0.05).The intestinal mucosal layer was very rich in folds,and the intestinal villi were more dense.With the increase of the proportion of PBM,the folds of intestinal mucosal layer decreased,and the intestinal villi became shorter and thinner.The expression of IGF-1and IGFBP2 in the PM24 group in the liver was significantly higher than those in the PM0 and PM60 diets(P< 0.05),but there was no significant difference in the expression of IGF1 R between the three groups(P > 0.05).In the intestine,the expression of IGF1 R in the PM24 group was the highest,and the expression of IGF-1 and IGFBP2 in the PM0 group was significantly higher than that in the PM24 and PM60 groups(P < 0.05).When the replacement level of PBM was 24%,the expression levels of Claudins,MLCK,MUC2 and ZO1 in the hindgut of juvenile N.albiflora were significantly higher than those in the PM0 and PM60 groups(P < 0.05);The expression on Occlaudin and JAM1 of PM0 and PM24 diet are both significantly higher than that of PM60 diet(P <0.05).In this trial,the growth performance of juvenile N.albiflora was the best,and the WGR and SGR were the highest in the diet of PM24.When the replacement level of PBM in the feed exceeds 24%,it will adversely affect the growth performance,intestinal tissue and gene expression of juvenile N.albiflora.Under the conditions of this trial,based on the weight gain rate,the broken-line model fitting shows that the optimal addition ratio of PBM in the feed of juvenile N.albiflora should be 21.02%. |
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