尾蟲類浮游動物之初探

Abstract

日本鰻 (Anguilla japonica) 為台灣重要的經濟養殖魚種，其孵化後仔魚營養來源一直都是大家關注的焦點，在前人的研究中曾發現柳葉鰻腸道中有larvacean houses的存在 (Otake et al., 1993)， 但台灣尚未有尾蟲類的相關生物培育資料，除了生態調查外，也沒有尾蟲活體運輸與培育方式。這是國內第一次有關尾蟲活體採集與培育Oikopleura dioica 的嘗試，本研究徒手在沿岸採集尾蟲，利用夜間光線差異現場挑出尾蟲，並使用自製旋轉擾動罐，提升運送時尾蟲的存活率從7%到50%，目前採用改良型拖網徒手沿岸採集已能成功採獲活體尾蟲，存活狀態良好，在實驗室的觀察中也發現第三天開始可以目視到所產生的後代，比較先前學者的研究以船隻拖網進行採集大幅減少成本的支出。 實驗中利用攝影機、光學顯微鏡與電子目鏡記錄尾蟲Oikopleura dioica快速的生活史(life cycle)(20℃，5天) ，從受精到孵化約207.5分進入前蝌蚪期(Early Tadpole)，尾部可抖動(但非波浪型擺動)，接著尾部迅速伸長，235.5分達後蝌蚪期(Late Tadpole)，385分後軀幹與尾部各部位器官分化完成(Metamorphosis)，尾部可以進行波浪狀擺動，並產生第一個House，開始濾食的生活，約在四天後達到成熟個體的階段。並在觀察中發現水流進入House及糞便排泄的方向與前人的觀察有所差異。 生殖腺的發育，由腔室的周圍開始向中央發展逐漸鼓漲，雄蟲鼓漲的精巢前有一生殖孔，雌蟲卵巢中卵粒逐漸透明清晰。胚胎的發育與溫度的高度相關關係，從第一次卵裂到成功孵化的時間，經線性回歸分析表示其關係式為y=-8.6099x+323.12，R2=0.6117(N=10)，並利用染色切片觀察卵巢內聚合囊(coenocyst)發育的情形，實驗室的培育觀察中，已有多次順利觀察到許多幼蟲產生，並成功以人工授精方式成功孵化，每批次200隻以上，可以達成高溫下(30℃)快速的人工受精並成功孵化(4hrs內)並累代繁殖(至少五代)，而尾蟲或尾蟲的house與鰻苗之間的關係，有待更進一步的探討。

Anguilla japonica is an important economic species, while the problem of nutrition source after hatching always evokes everyone's attention. In previous studies had found larvacean houses existence in the leptocephalus gut (Otake et al., 1993). However, in Taiwan no one has tried to collect live larvacean for rearing.This report is the first time about the living larvacea collection and breeding attempts in our lab. The results show that we can collect Oikopleura dioica or the other larvacean by hand along the coast. We collected larvacean at night by flash light, and further retain in the homemade rotation tank to enhance the larvacean’s survival rate from 7% up to 50% when transport the animal,and began to cultivate after one to three days. Under 20℃after fertilization the embryo undergoes rapid cleavage cycles and the tailbud stage hatches from the chorion 207.5 minutes postfertilization. During the tadpole stages the tail became longer and longer and organogenesis occurs.At metamorphosis, 385 minutes postfertilization, the tail shifts from a linear posteriorly directed orientation relative to the trunk to a more orthogonal position, with the end of the tail lying in the same direction as the mouth. Immediately following tailshift, the first house is inflated. The relationship of embryonic development of Oikopleura dioica and temperature by linear regression analysis is y = -8.6099x + 323.12, R2 = 0.6117 (N = 10) .Both directions of water entering and feces discharging are different from the previous studies in observation about the house. During the Experiment we used camera, optical microscope and electronic eyepiece to record Oikopleura dioica’s .larvacean has a simplified anatomical organization, remains transparent throughout an exceptionally short life cycle of less than 1 week and exhibit high variable fecundity. By using histological method to observe the ovary development of coenocyst. Growing oocytes defined a selective kinase environment in the common coenocyst cytoplasm. Vitellogenesis preceded the timing of oocyte selection among excess germ line nuclei. This unique feature enables late adjustment of oocyte number in accordance with the cytoplasmic volume of the germline cyst accumulated during vitellogenesis. Through current equipment and methods,we can bred at least five serial generations by artificial insemination.The relationship between larvacean (houses) and eel larvae, needs further research.