盐度影响香鱼仔鱼生长的生理机理及转录组研究

Ayu (Plecoglossus altivelis), possessing a special smell and good taste, is considered a popular and highly valued edible fish in Asia. In recent ayu culture, the larvae of ayu live in brackish water during two months post-hatching and the juveniles live in fresh water. Our previous investigation found that ayu can live in fresh water throughout life cycle. However, the body length and weight of ayu larvae in fresh water were only 71.9% and 37.6% of that in brackish water. Here, we try to investigate the mechanisms of brackish water induced rapid growth in ayu larvae. After 8 weeks of culture, energy metabolism, hormones in serum, food intake and food conversion will be measured in ayu larvae cultured in fresh, brackish and sea water. More importantly, we will use a Illumina HiSeq? 2000 sequencing method to investigate differentially expressed genes between ayu larvae cultured in brackish and fresh water. We will further reveal functional distribution and pathways of the differentially expressed genes of the two libraries by GO and KEGG analysis. The physiological phenotypes will be used to identify candidate gene pathways from transcriptome analysis leading to the phenotypic alterations induced by salinity change. Moreover, the tempo-spatial expression of differentially expressed genes will be analysed by real time PCR and in site hybridization. The recent investigation will illustrate the mechanism of brackish water induced rapid growth of ayu larvae and guide the better ayu breeding. This work will also enrich our knowledge in ayu amphidromous life cycle.

香鱼是东亚地区特有小型名贵经济鱼类，具有降海洄游习性，环境盐度对香鱼的人工育种和养殖有重要影响。申请人前期研究发现香鱼仔鱼孵化后在淡水中生长8周，其体长和体重分别仅为咸淡水生长个体的71.9%和37.6%。因此本项目拟解析盐度影响香鱼仔鱼生长的机理。研究淡水、咸淡水和海水养殖香鱼仔鱼生理变化，包括能量代谢、激素水平、食物摄取和转化效率。使用高通量测序技术测定淡水和咸淡水养殖的香鱼仔鱼转录组，分析表达差异基因并进行功能注释。给合生理指标挖掘关键通路基因，采用荧光定量PCR和原位杂交分析盐度影响香鱼仔鱼生长过程中关键通路基因的时空表达。本项目将探明盐度调控香鱼仔鱼生长的功能基因和通路途径，可为香鱼育种和养殖提供理论指导，丰富鱼类盐度适应理论。

香鱼是东亚地区的一种洄游鱼类，幼鱼生活在咸淡水，而成鱼生活在淡水中。本项目主要研究发现咸淡水养殖香鱼仔鱼的生长速度超过淡水养殖的香鱼仔鱼，进而通过检测香鱼仔鱼的基础生理指标和转录组表达来研究生长速度差异的机制。研究发现淡水养殖香鱼仔鱼的生长激素（growth hormone，GH）、摄食率下降，而皮质醇（cortisol，COR）、三碘甲状腺原氨酸（triiodothyronine，T3）、四碘甲状腺原氨酸（tetraiodothyronine，T4）、耗氧量上升。同时通过检测咸淡水和淡水养殖香鱼的转录组表达，共组装获得172,623条序列。其中7条通路与能量代谢和神经内分泌系统有关，包括辅酶和维生素代谢、氨基酸代谢、能量代谢、脂代谢、神经系统和内分泌系统。发现甜菜碱-同型半胱氨酸转甲基酶（betaine-homocysteine S-methyltransferase 1，BHMT）、果糖-二磷酸醛缩酶（fructose-bisphosphate aldolase B，aldolase B）、脱碘酶（iodothyronine deiodinase，ID）、阿黑皮素（pro-opiomelanocortin，POMC）、钠钾ATP酶（Na+-K+ ATPase，NKA）和酪氨酸氨基转移酶（tyrosine aminotransferase，TAT）基因在淡水养殖后均上调。此外，B型钠尿肽（b-type natriuretic peptide，BNP）和转胶蛋白（transgelin）在淡水养殖后均下调。这些结果说明淡水养殖香鱼仔鱼生长缓慢，可能是由于内分泌系统产生的激素抑制了食物摄入，同时氨基酸和脂肪代谢增加，以及维持渗透压而消耗更多ATP共同导致的。