| Summary: | 碩士 === 國立臺灣大學 === 漁業科學研究所 === 102 === Natural stocks of A. japonica’s glass eels have decreased dramatically due to overfishing, environmental destruction and change of ocean conditions in recent years. Therefore, in order to reduce the consumption of wild glass eels, developing techniques of artificial production for improving Japanese eel farming industry has become a major goal. As a result of no appropriate feed conversion method currently applied on the breeding process of eel larvae, the growth rate and survival rate are extremely low. In this study, three leptocephali, five preleptocephali, and ten embryos were collected near the Mariana ridge by cooperating with the Japanese team, and one glass eel was collected at the estuary of Yilan River. All the samples were submitted for RNA-seq by next-generation sequencing for reconstructing complete transcriptome of Japanese eel. Furthermore, the expressions of digestive enzymes and nutrient transporters existing in small intestine were investigated for realizing the digestive and absorptive capacities of Japanese eel larvae.
A total of ~30 million raw reads (100 PE) were generated in our experiment and assembled into 224,043 transcripts after eliminating adaptors and low quality reads. Moreover, 116,146 transcripts were predicted to have open reading frames, and these putative protein-coding transcripts were submitted to blast against nr database. Subsequently, 70,096 transcripts were found positive hits, 90.2% of which were homologous genes of Actinopterygii. Besides, our analytic results showed that the digestive capacity of protein is terrific in preleptocephalus, but the digestive capacities of carbohydrate and lipid are very poor. In addition, a similar pattern is also found in leptocephalus, but the digestive capacities of carbohydrate and lipid are relatively better than in preleptocephalus. Furthermore, glass eel has average capacities for digesting protein, carbohydrate and lipid. In nutrient absorption, the absorptive capacity of amino acids is actually the best in preleptocephalus and leptocephalus, followed by the absorptive capacity of glucose which is better than cholesterol. Additionally, in glass eel, the absorptive capacity of amino acids is also superb, but the absorptive capacity of glucose is significant decreased than previous stages. Interestingly, the cholesterol transporters almost have no expression in glass eel. The digestive capacity of carbohydrate is poor in preleptocephalus and leptocephalus, but absorptive capacity is good. This may be related to gut microbiota in them, or they prefer to directly absorb monosaccharide or disaccharide in the food. Moreover, the digestive capacity of lipid is terrific in glass eel, but the absorptive capacity of cholesterol is poor, which may be associated with the well-functioned lipase and structural properties of plasma membrane because the small molecules of lipid end-products usually can pass through the plasma membrane. Based on above results, much useful information can be provided for developing artificial feed and feed conversion method. An online database for accessing the de novo assembled transcripts of four transcriptome data and annotated result of each transcript has been established. This database will be public for researching community of Japanese eel, and it can assist researchers in studying fundamental eel biology and artificial production.
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