Studies On Vitellogenesis Of Cultured Chinese Sturgeon

Chinese sturgeon (Acipenser sinensis Gray) is one of the largest anadromous species. It was mainly distributed in East China Sea, Yellow Sea, Pearl River and the trunk stream of Yangtz River. It spends most of its life in the sea, but spawns in the rivers, mainly in the Yangtze River. In the recent years, dramatic decline in the wild sturgeon's population was attributed to the dam construction, overfishing and water pollution. Artificial propagation of the wild Chinese sturgeon has achieved success, which was very important for the implementation of artificial enhancement. Besides, according to a news report, the close-cycle captive breeding of Chinese sturgeon was completed in 2009. However, the gonadal development rule of Chinese sturgeon and the vitellogenesis which is critical for the juvenile developing to mature have not been reported yet. This thesis analyzed the site of vitellogenin synthesis by histological observation of gonad and electron microscope observation of the process of vitellogenesis, and corroborating endogenous and exogenous vitellogenesis by molecular techniques. Conclusions from the studies are as follows:1. The gonadal development of cultured Chinese sturgeon (age:1-10 years) was observed 10 years old female has the maximal oocyte diameter, which was about 500um. However, most of oocyte diameter were from 200 to 400 um. There were one or two follicle velums around the oocytes. Most of them were in the gonadal development stageâ…¡, some were in the process from late stageâ…¡toâ…¢. The vitellogenesis and deposition of the yolk are critical for Chinese Sturgeon developing to mature2. Early Oogenesis in Chinese Sturgeon(Acipenser sinensis) was observed by light microscope and transmission electron microscope. The results indicated that the vitellogenesis started in the primary oocyte phase, and the characteristic substance of oogenesis (Nucleoli-like body) occurred in the oogonia phase. Moreover, according to the relationship between the distribution of Nucleoli-like body in cytoplast and mitochondria, early oocyte can be divided into different development stages. In early oocyte development stage, Nucleoli-like body disappeared gradually, mitochondria increased, and extracellular plasma membrane and connective tissue appeared. In late primary oocyte phase, yolk nucleus had disappeared, and the observation by electron microscopy found that mitochondria, endoplasmic reticulum, Golgi body and other organelle were involved in the formation of Chinese sturgeon yolk, yolk granules and lipid droplets appeared in the cytoplasm, and finally yolk granules merged into large yolk granules. The oocyte ingest extracellular material via micropinocytotic pits and vesicles. These structures apparently fuse to form tubules which then coalesce into large yolk droplets.3. Endogenous and exogenous vitellogenesis was corroborated by molecular techniques. Cultured female Chinese sturgeon from 1 to 10 years old and 6 age-group male individuals were used to confirmed the gonadal development stage by histology. In the present study, total RNAs were isolated from ovary and hepatic of cultured Chinese sturgeon at different ages. Expression of vitellogenin mRNA was identified by RT-PCR amplification method. Successful amplification was accomplished by using both ovary and hepatic. It could be concluded that both female and male individuals were the specific site of vitellogenin synthesis. The expression of vitellogenin mRNA increased in the ovary with age increasing from 1 to 10 years old. The expression of vitellogenin mRNA of the land 2 years old juveniles was the lowest, but the expression of vitellogenin mRNA was the highest in 10 years old sturgeon, and was obviously higher than the expression of the wild Chinese sturgeon vitellogenin mRNA in the ovary. The expression of vitellogenin mRNA in the female Chinese sturgeon hepatic was tested. Excepted the 1 year-old juveniles, the expression of vitellogenin mRNA was identified in all 2-7 years'juveniles, and there were no significant differences in the expression. The expression of vitellogenin mRNA in the male Chinese sturgeon gonad was also tested in 1,3,4,5,9,12years old sturgeons, and it was found that excepted 1 year-old juveniles, the expression of vitellogenin in mRNA was identified in all of the other juveniles, and no significant differences exist in the expression. Under normal condition, a little VTG existed in male sturgeon. This also confirmed that vitellogenin in testis supplied nutrition to the sperm of the male sturgeon.4,Experimental results had verified that there were two synthetic modes of Chinese sturgeon vitelline, including endogenous and exogenous vitellogenesis. And endogenous vitellogenesis was the main source of vitelline-in the late gonadal development. The gonad of Chinese sturgeon which was cultured 10 years had not matured yet. This suggested that the key factor which was related to domestication of First Filial Generation and Brood stock Culture of Chinese sturgeon was how to speed up the gonada development and deposition of the yolk. So the deposition of the nutrition for gonadal development in Chinese sturgeon was critical for the close-cycle captive breeding. This experiment was instructional for the artificial domestication of First Filial Generation of Chinese sturgeon.