Study On Annual Gonad Development Of The Laboratory-reared Amphioxus (Branchiostoma Japonicus) And Growth, Gonadal Devlopment Of Gynogentetic Olive Flounder

Annual gonad development of the laboratory-reared amphioxus(Branchiost- oma japonius) was observed using histological method, and compared with the gonad development of wild amphioxus in the corresponding period of time. Then their sex ratios were preliminary investigated in both laboratory-reared and wild stocks. In the meanwile, the growth conditions of induced olive flounder(Paralic- hthys olivaceus)gynogenentic stocks including a meiogynogentic stock, a meiogy- nogentic family and a mitogynogenetic stock were tracked. The gonad developm- ent of the meio gynogenetic individuals of 2 year old was also anatomically and histologically studied.Healthy amphioxus with developed gonads were selected from Shazikou natural sea area of Qingdao in June 2008, and cultivated in our laboratory at the Institute of Oceanology, Chinese Academy of Sciences for more than one year. The samples were collected and measured, and then fixed monthly. Histological structure of amphioxus gonads was observed under light microscope. The results showed that, from Sep. 2008 to Aug. 2009, there were nearly no changes in total length of amphioxus under indoor condition. And their body weight were also no changes during this period except the reproduction period. There were significant increases of amphioxus body weight in the V phase of ovaries or testis(P<0.05), and their body weight would dropped to the former weight after reproduction. Amphioxus could breed only one time each year and the breeding period is from June to July in summer. The laboratory-reared amphioxus could release eggs and sperm spontaneously. Then their ovaries and testes were in the emission later stage, and went through I, II, III, IV and V phases in the next round of gonadal development. It was also found that ovary development did not accord with testis development until the IV phase, and testis usually developed earlier than ovary. In addition, amphioxus testis stayed in the IV phase for a longer time (from March to May) compared with ovary (from April to May). In order to compare with the gonadal development condition of wild amphioxus, samples at the corresponding time period from Shazikou were caught, fixed and analyzed in November, January, March, and June The results showed the gonad development of laboratory amphioxus was basiclly consistent with that of the wild ones. According to the statistical analysis, the annually laboratory-reared amphioxus had 64 females and 58 males, and ratio of female and male was 1:0.91. But the analysis results from the wild amphioxus collected and fixed in November 2008, June 2009 and March 2010 showed that there were 21 females and 15males, and ratio of female and male was 1:0.71. The above sex ratios, expecially the latter, were very different from the results of reported other amphioxus population structures. Then, the sex ratio in Qingdao amphioxus is needed to observe more data for the further study.According to tracking observation of induced meiogynogenetic and mitog- ynogenetic olive flounder, there was peak mortality between 35-52 days after hatching; there were also significant differences in both total length and body weights among individuals of mitogynogenetic stock in17 months age(P<0.05). Furthermore, the ovaries of 23 2-year old meiogynogenetic flounders were anatomically observed. The results showed that there were 9 individuals (9/23, 39.13%) with normal ovaries, and the remaining 14 individuals have abnormal ovaries. The malformation phenomena of ovary could be divided into two types. Both sides of ovary are asymmetric, with only one side or one side of the growth retardation(9/23, 39.13%), and the other type is that both sides of ovary were in growth retardation compared with control flounder ovary(5/23, 21.74%). By the histological observation and aromatase immunohistochemical location, the ovaries of 2-year old meiogynogenetic individuals were not significantly different from those of control female except the slower development. Whether induced gynogentic flounders could spawn or not is still required for further observation.