著者

鈴木 伸洋

出版者

東海大学

雑誌

東海大学紀要. 海洋学部 (ISSN:13487620)

巻号頁・発行日

vol.2, pp.25-30, 2004-07-31

被引用文献数

1

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It is well known that bitterlings deposit eggs in the gill cavity of freshwater bivalves. After hatching the larvae stay and develop in the bivalve, until well-developed swim out from the bivalve. The development of the bitterling Rhodeus spinalis is surprisingly few. This study attempts to clarify the early bitterling ontogeny of R. spinalis collected from Hainan Island, southern China. The development of egg and larvae of R. spinalis was observed under controlled water temperature of 22℃. The ripe unfertilized egg is nearly elliptical shaped, like the egg of R. ocellatus which is elliptical, and the yolk remains a opaque yellow rather than a pale yellow color, measuring about 3.0mm in length, 1.8mm in breadth. R. spinalis is shared a pair of wing-like processes which the yolk is anteroventrally convex with other Rhodeus larvae during the advanced stages (i.e. 12day-old). The anterior part of the yolk sac found in hatched larva of R. spinalis has plumped up, unlike other Rhodeus larvae shaped like an arrow. The larvae began to feed, when larvae reached the free swimming stage, so that larvae emerge from freshwater bivalve in the wild and the dorsal and anal fin rays are formed completely from 26 to 28 days after hatching. The time of the formations is later than other Rhodeus larvae (i.e.18-22day-old). Melanophores on the dorsal fin aggregated at its anterior region become a black spot in juvenile stage (i.e.44day-old), and the spot is true round-shaped unlike spots of other Rhodeus larvae which are ellipse-shaped in R. atremius atremius, R. atremius suigensis, R. notatus, new moon-shaped in R. ocellatus ocelllatus and nearly rectangle-shaped in R. sinensis.人工授精による22℃の飼育下でのRhodeus spinalisの完熟卵形および発育形態について報告した. 本種の完熟卵形は, 紡錘形をしていた. Rhodeus spinalisの孵化直後仔魚は, Rhodeus属の他の種と同様に翼状突起がよく発達していた.しかし, 卵黄囊の前端部は比較的卵黄量が多く存在し, 太丸く突き出る点で既往のRhodeus 属の孵化直後仔魚の形態と識別できると考えられた. 本種は26~28日齢で二枚貝から浮出して自由遊泳期になるものと推定され, この日数はRhodeus 属のどの種よりも遅かった. 背鰭の稚魚斑を形成する黒色色素胞叢の分布は第3不分岐軟条から第5,6分岐軟条で, その分布の後端は鰭基底に達しない. また, 背鰭稚魚斑の形態が楕円というよりは真円に近い円形である点でいずれのRhodeus属の種のものとも識別できるものと考えられた.