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Abstract |
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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 of22°C.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 about3.0mm 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 from26to28days 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. |
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