| The Japanese eel is a widely distribution of migratory fish,which is rich in nutrition.Duing to a long-term fishing and the deterioration of living environment,the number of them is declining.At present,there are many difficult points of the Japanese eel artificial breeding were not breakthrough.After artificial maturation,the liver of the female eel were enlargement.Liver is the main organ which synthesizes and secretes vitellogenin.Vitellogenin will change into yolk protein,which is the first nutrient for the larvae.Therefore,the liver change of the female eel is neccessary to the larvae survival.Through the optical sectioning and transmission electron microscope to observe the female eel’s liver which in different spawning.In order to verify whether in the liver injury,we tested the ALT,AST,and SOD enzyme activity.In order to verify whether the different content of vitellogenin would result different spawning,we tested the vitellogenin in each group.The opening bait of larvae has been a difficult point of artificial work.Through the nutrient analysis of the eel’s egg,we realized the nutrient theory demand of eel’s larvae.With the improvement of the transcriptome sequencing technologies,through the larvae transcriptome sequencing,digestion and absorption of gene analysis,provides the basis of larvae nutrients for the future exploration.1.Through two slice observation we found that compared with the control group,there are some mainly differences: first,the deformation of liver cell,the cytoplasm reduced;Second,there were mass lipid droplets in liver cells;Third,too many rough endoplasmic reticulum in livers;Fourth,the glycogen particles decreases.So many lipid droplets appeared suggested that the vitellogenin was synthesis,and the better situation of spawning,the lipid droplets were bigger.We also found the volume of lipid droplets in difficult spawning were smaller than natural spawning and artificial spawning,which suggests the vitellogenin of difficult spawning was less than they.Through comparison of degeneration group and natural spawning,artificial spawning,we found the cytoplasm was richer than they,which was closed to the control group.That is to say,the liver cells can recover if the steroid induction stops.The AST enzyme activity in the control group,difficult spawning,natural spawning,artificial spawning,degradation group were(78.20±2.01),(87.73±3.78),(86.33±6.35),(83.21±1.48),(81.80±1.78)U/L,respectively.Compared with the control group,the enzyme activity of natural spawning and difficult spawning were significantly high(P < 0.05).The ALT enzyme activity in the control group,artificial spawning,degradation group,natural spawning and difficult spawning were(12.80±0.56),(19.57±1.84),(19.10±2.51),(18.6±1.37),(18.53±2.10)U/L,respectively.Compared with control group,the enzyme activity of the other groups were significantly high.The SOD enzyme activity in the control group,difficult spawning,natural spawning,degradation group,artificial spawning were(63.35±2.50),(95.29±6.14),(81.13±8.49),(79.97±3.31),(78.45±9.87)U/mL,respectively.Compared with the control group,the enzyme activity of the other groups were significantly high.Compared with the difficult group,the enzyme activity of natural spawning,degradation group and artificial spawning were significant.That is to say,during the artificial steroid induction,the liver of female eel was damaged,especially in difficult spawning.In the control group,natural spawning,artificial spawning,difficult spawning,degradation group,the vitellogenin content in serum were(2.49±0.19),(4.18±0.19),(4.26±0.15),(3.48±0.50),(2.63±0.21)μg/mL,respectively.Except the degradation group,the contents of the rest groups were significantly higher than control group.Compared with the difficult spawning,the contents of natural spawning,artificial spawning were significant.In liver,the contents of each group were(6.58±0.29),(7.20±0.55),(7.05±0.72),(6.62±0.59),(6.63-0.14)μg/mL,respectively.And there was no significant difference between each group.The gonads,the content of each group were(387.73±3.84),(454.57±17.08),(418.94±6.50),(419.16±16.20),(418.24±17.87)μg/mL,respectively.Compared with the control group,the rest of groups were significantly improved.There was a significant difference between degradation group,difficult spawning and artificial spawning,natural spawning.That is to say,in the late gonadal development,the ability of the liver synthesis vitellogenin has fallen,and the content of vitellogenin directly influences the spawning.2.From the nutrient analysis of artificial spawning eggs,the nutrient theory demand of eel’s larva protein and fat in the feed were 59.62% and 40.86%,respectively.Under the dry basis,the content of total amino acid(TAA)was 8.07%,essential amino acid(EAA)was 3.19%,nonessential amino acid(NEAA)was 4.88%.Compared with other fish eggs,the amino acid content was low.So,we should regard the amino acid content of this experiment as the lowest feed ratio,and add the contents of the amino acids in feed,especially the first limiting amino acids,valine.Under the fresh weight basis,DHA content was 25.98%,the EPA content was 4.27%,the EPA + DHA content was 30.25%.In eel’s larva feed ratio,we can appropriately increase the DHA content for promoting growth.The EPA content of this study can be as a theoretical reference.In conclusion,the nutrient theory demand of eel’s larva can only be taken as a reference.The nutrients actual requirements still need to determine by different situation.3.The transcriptome of five growth stages(0dph、3dph、6dph、9dph、12dph)of Japanese eel’s larva were sequenced in this study,then the transcriptome libraries(A、B、C、D、E)established.RNA-seq analysis yielded 102941 unigenes with an average length of 856.6bp,the GC content of the transcriptome was 54.92%.Metabolism and Genetic information processing were the most on KEGG annotation,there are 33487 differentially expressed unigenes were detected between A and B,;3773 differentially expressed unigenes were detected between B and C;1506 differentially expressed unigenes were detected between C and D;84 differentially expressed unigenes were detected between D and E.We also selected a part of unigenes which enriched in digestive system to analysis and speculated that the metabolism of nutritive substance of eel’s larva in different periods.The digestion and absorption levels of protein and sugar of hatchling eels gradually increased,and the digestion and absorption levels of fat were higher in the first 3 days,and then gradually decreased and stabilized. |
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