美洲鲥内源性营养阶段脂肪酸组成及利用

Composition and utilization of fatty acids during the endogenous nutrient stage of Alosa sapidissima

为掌握美洲鲥(Alosa sapidissima)发育早期内源性营养阶段的脂肪酸变化及利用规律,采用生化分析手段,检测和分析美洲鲥的胚胎(原肠期)、0日龄和4日龄仔鱼(摄食前)的粗脂肪含量和脂肪酸组成。结果显示,随着个体发育,美洲鲥内源性营养阶段的水分含量显著降低、鲜质量的粗脂肪含量显著上升、干物质的粗脂肪含量微弱升高,而单个个体的粗脂肪含量显著下降,数值从胚胎的60.04μg下降到4日龄仔鱼的41.91μg。胚胎孵化破膜期间,C18∶1n9c和C22∶6n3(DHA)大幅减少。仔鱼出膜后到开口摄食前,对脂肪酸的利用优先顺序为n6PUFA>MUFA>SFA>n3PUFA,C18∶2n6c、C18∶3n6、C16∶0和C18∶1n9c被先期利用,而对n3PUFA的利用极低(特别是EPA+DHA)。研究表明,美洲鲥胚胎孵化出膜期间,EPA被先期暂存,而DHA被大量利用;仔鱼出膜后,n3PUFA被优先保存,特别是EPA+DHA。因此,建议美洲鲥亲本产前培育和产卵期间,增加投喂富含n3PUFA(特别是DHA)的饲料,以增加其受精卵营养储备,提高美洲鲥开口前仔鱼的成活率。

In order to understand the fatty acids composition,changes and utilization rules during the endogenous nutrient stage of American shad A.sapidissima,biochemical analysis methods were used to detect and analyze the crude fat content and fatty acids composition of A.sapidissima in different developmental stages:embryos during the gastrula stage,newly hatched larvae 0-day-age,and before feeding larvae 4-day-age.Results showed that the individual crude fat contents of A.sapidissima during the endogenous nutrient stage were high(41.91μg-60.04μg),the larvae consumed 30.20%of the crude fat before feeding;with the individual development,the moisture content reduced significantly(P<0.05)(the value from 96.42%to 88.25%),the crude fat content of dry matter increased slightly(P>0.05)(the value from 16.33%to 19.13%),the crude fat content of fresh quality increased significantly(P<0.05)(the value from 0.58%to 2.25%),the individual crude fat contents decreased significantly(P<0.05)(the value from 60.04μg to 41.91μg)during the endogenous nutrient stage.The top 4 fatty acids relative content was C16∶0(21.65%-23.06%),C18∶1n9c(19.02%-20.93%),C22∶6n3(DHA)(15.02%-18.20%),and C18∶2n6c(12.33%-14.43%)during the endogenous nutrient stage of A.sapidissima.The C16∶0 relative content of 0-day-age larvae was significantly higher than that of embryos and 4-day-age larvae(P<0.05),while there was no significant difference between embryos and 4-day-age(P>0.05);the relative contents of C18∶1n9c and C18∶2n6c significantly decreased with the individual development(P<0.05);the relative contents of C22∶6n3(DHA)significantly increased(P<0.05)with the development of ontogeny,the C22∶6n3(DHA)relative content of 4-day-age larvae was significantly higher than that of embryos and 0-day-age larvae(P<0.05),while there was no significant difference between embryos and 0-day-age(P>0.05).Although the relative content of C20∶5n3(EPA)was not high(1.05%-1.49%),the relative content of C20∶5n3(EPA)significantly increased with the individual development(P<0.05).This also resulted in a significant upward trend of DHA+EPA with the individual development(P<0.05),DHA+EPA relative content of 4-day-age larvae(19.69%)was significantly higher than that of embryos(16.07%)and 0-day-age larvae(16.63%)(P<0.05),while there was no significant difference between embryos and 0-day-age larvae(P>0.05).The SFA relative content of embryos(32.39%)was significantly lower than that of 4-day-age larvae(33.53%)(P<0.05),while there was no significant difference between 0-day-age larvae and embryos or 4-day-age larvae(P>0.05).The relative content of MUFA was relatively low(20.92%-22.82%)and significantly decreased with the individual development(P<0.05).The relative content of PUFA was rich and stable(44.76%-45.55%),and there was no significant change in the PUFA content among embryos,0-day-age and 4-day-age larvae(P<0.05).The ratio of∑SFA to∑UFA of 4-day-age larvae(0.50)was significantly higher than that of embryo(0.48)(P<0.05).The ratio of∑n3PUFA to∑n6PUFA increased significantly with individual growth and development(P<0.05),and the value increased from 0.69 to 0.94,the ratio of∑n3PUFA to∑n6PUFA of embryos and 0-day-age larvae was significantly lower than that of 4-day-age larvae(P<0.05),while there was no significant difference between embryo and 0-day-age larvae(P>0.05).The top 4 fatty acids absolute content in individual was C16∶0,C18∶1n9c,C22∶6n3(DHA)and C18∶2n6c during the endogenous nutrient stage of A.sapidissima.With the individual development and the shedding of egg membrane,the absolute content of C24∶1n9 decreased slightly at first(P>0.05)and then increased significantly(P<0.05),and the absolute content of C15∶0 showed a significant trend of first decrease and later increase(P<0.05),the absolute content of C17∶1 increased slightly at first(P>0.05)and then decreased significantly(P<0.05),the absolute contents of C17∶0,C20∶0,C20∶4n6,C20∶5n3(EPA)and C22∶6n3(DHA)had no significant changes(P>0.05),the absolute contents of the other 14 fatty acids in individual showed a significant downward trend(P<0.05).The superposition effect of the decrease of most fatty acids resulted in a significant decreasing trend of absolute contents of the SFA,MUFA and PUFA in individual with individual development(P<0.05).In addition,the absolute contents of EPA+DHA and∑n3PUFA showed no significant change with the individual development(P>0.05),while the absolute content of∑n6PUFA showed a significant downward trend(P<0.05).During the embryo incubation period of A.sapidissima,C18∶1n9c(256.31μg and 20.40%,respectively)and DHA(132.23μg and 14.64%,respectively)reduced largely.From the point of utilization amount and rate,after the larvae emerged from the membrane to the opening before feeding,there was a certain priority in the use of fatty acids:n6PUFA(295.41μg and 23.81%,respectively)>MUFA(224.72μg and 20.37%,respectively)>SFA(279.79μg and 16.59%,respectively)>n3PUFA(38.67μg and 4.19%,respectively),especially C18∶2n6c(207.48μg and 28.64%,respectively)and C18∶3n6(48.77μg and 26.53%,respectively)in n6PUFA,C16∶0(256.35μg and 22.02%,respectively)in SFA and C18∶1n9c(201.86μg and 20.18%,respectively)in MUFA were used in priority.While the utilization amount and rate of n3PUFA were extremely low(38.67μg and 4.19%,respectively),especially EPA+DHA(18.26μg and 2.17%,respectively).Researches showed that the EPA was preserved in priority but DHA was used largely during A.sapidissima embryo incubation period;n3PUFA(especially EPA+DHA)was preserved in priority after the larvae emerged from the membrane.∑n3PUFA/∑n6PUFA was lower(0.69-0.94)during the endogenous nutrient stage of A.sapidissima,and this showed the fatty acids characteristic of freshwater fish.In the antepartum cultivation and spawning period of brood stock,it is suggested to supplement diets enriched with n3PUFA(especially DHA)in time in parents bodies to enhance the nutrition accumulation and increase the nutrient reserve of the fertilized egg,and then to improve the survival rate of A.sapidissima larvae before feeding.