| Chinese sturgeon(Acipenser sinensis)is an endangered species,and has been listed as a Grade I protected animal in China.Broodstock culture of Chinese sturgeon,has already been developed in China,but sexual maturation in controlled breeding is a technical difficulty.Gonads of most females usually remain in stage II,only very few fish can develop their ovaries to stage III or IV.Thus,in order to protect this species better,it is vital to develop solutions to the poor sexual maturity.This article starts from the angle of nutrition regulation,analyze the nutrition(protein,lipid,fatty/amino acid profile)content in tissues of muscle,liver and gonad obtained from farmed Chinese sturgeon with gonad development at stage II and discern the key nutrients for gonad by comparing the nutrients between tissues and between fish at different gonad stage.Then,investigate the effects of different dietary lipid levels on gonad development of female Chinese sturgeon and the possible regulative mechanism of lipid on gonadal development through the periodic determination of growth performance,gonadal development status,serum hormone and biochemistry levels and a combination of gonadal transcriptome analysis and serum metabolome analysis after 18 month's feeding.The main results are as follows:1.Preliminary identification of the key nutrients for Chinese sturgeon gonadal development.Chinese sturgeons were reared in an outdoor circular cement pool with temperature ranging from 8oC to 26oC,and were fed with 70% artificial diets and 30% frozen forage fish at a feeding rate of 0.2-1.5% body weight according to water temperature.Three male and three female were sampled for analysis.The results are as follows: Lipid content in gonad was significantly higher than that in other tissues both in male and female(P<0.05).The content of protein in gonad of male and female was significantly lower than that in muscle(P<0.05).The total content of mono-unsaturated fatty acids(MUFA)in femalewas significantly higher than that in male(P<0.05),while the total content of n-6 PUFA in female was significantly lower than that in male(P<0.05).Palmitic acid(C16:0)and oleic acid(C18:1n9)were the major saturated fatty acid(SFA)and MUFA,respectively,both in female and male.The contents of C18:2n6,C20:4n6(ARA),C18:3n3 and C22:6n3(DHA)in gonad from male were significantly higher than those from female(P<0.05).The contents of ARA,EPA and DHA in gonad were lower,and they may play the pivotal role in gonad development.By in comparison with the nutrients of ovary in broodstocks at stage III and stage IV and the eggs at stage IV,the present study suggests that lipid and fatty acids profile in fish body are vital to the gonad development and proper improvement of lipid nutrition of broodstock diet to provide sufficient energy and essential fatty acid would be benefit for gonad development of Chinese sturgeon.2.Effect of dietary lipid level on gonad development of female Chinese sturgeonAbout 10 years old Chinese sturgeons with gonad development at stage II-in three groups were fed with three isonitrogenous(46%)experimental diets containing three lipid levels of 10%,14% and 18%,respectively.Feeding experiment was conducted for 24 months,and gonad,muscle and serum were collected at the experimental time of 6,12,18 and 24 month for histological analysis and serum biochemical analysis.Serum metabolomics and gonad tissues transcriptomics analysis was conducted at 18 month.The results show that the specific growth rate in 10% group was significantly higher than that in group of 18%(P<0.05).Significantly higher diameter of oocyte and large amount of lipid droplets in oocyte were observed in 18% group,egg of stage ? were also detected in 18% group.The content of muscle lipid droplets were significantly decreased in group18% compared to group of 10% and 14% both at 12 and 24 month(P<0.05).Serum triglyceride content in 18% group were significantly higher than that in group of 10% and14% both at 12 and 18 month(P<0.05).Estradiol content in group 14% was significantlyhigher than that in 10% and 18% group at the first three sampling times(P<0.05).Gonad tissues transcriptome showed a large number of differential genes among three groups,and the major metabolic pathways annotated with differential genes are arachidonic acid metabolism,terpenoid Backbone biosynthesis,steroid biosynthesis,Ovarian steroidogenes.In addition,oocyte growth related genes(bmp15,gdf9),lipid droplets deposition related genes(lpl,fatp4,fabp1),yolk generates related genes(vtgr,cstd,cstb),cholesterol synthesis related genes(hmgcs,lss),arachidonic acid metabolism related genes(lox12,lox15,pge2),which mRNA expression in 18% group are significantly higher than those in the other two groups.The results of serum metabolomics and gonad tissues transcriptomics indicated that 14% dietary lipid level is beneficial to steroid hormone synthesis,18% dietary lipid level facilitate arachidonic acid metabolism and cholesterol biosynthesis.The results above indicate that 18% dietary lipid level is desired to improve gonad development of female Chinese sturgeon.In conclusion,the present study indicated that the amount of lipid stored in Chinese sturgeon play an important role in the gonadal development,DHA and ARA are key nutrients for the gonad development of Chinese sturgeon broodstocks.18% dietary lipid level can enhance lipid metabolism,arachidonic acid metabolism,improve lipid deposition and oocyte growth in the process of gonad development of female Chinese sturgeon,and is beneficial to gonadal maturation of female Chinese sturgeon. |
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