ウナギ目魚類の卵期および前葉形仔魚期における油球の性状

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タイトル別名
  • ウナギモク ギョルイ ノ ランキ オヨビ ゼンヨウケイ シギョキ ニ オケル
  • Location and numbers of oil globules in unfertilized and fertilized eggs, and larvae in the preleptocephalic stage in the Order Anguilliformes

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Most fish in the order Anguilliformes can be classified into three groups depending on whether oil globules present or not in unfertilized and fertilized eggs, and in larvae in the preleptocephalic stage period. In one group, eggs lack oil globules; in another group, eggs have a single large oil globule and, uncommonly, a few small oil globules; in the third, eggs have many small oil globules. In a study due to facilitate species identification of eggs and larvae collected in field investigations, we examined such oil globules in eggs and larvae more closely. In all species, in four of the five families examined (Synaphobranchidae, Congridae, Muraenesocidae, and Ophichthidae) oil globules were found in eggs still in the ovaries. The exception was Muraenidae, in which oil globules could not found during oogenesis. In artificially fertilized eggs examined, oil globues were decreased in number by fusion during developing period. Eggs of Ariosoma anagoides and A. shiroanago major (family Congridae) had only one large oil globule until optic vesicles appeared, well before hatching. However, in the same family, Gnathophis nystromi nystromi eggs had 12 to 40 oil globules just before hatching, with some moving toward the vegetal pole during development and later scattering again into the yolk sac. In Mystriophis porphyreus (family Ophichthidae), there were at least 20 oil globules before hatching, they moved as did those in Gnathophis nystromi nystromi. In larvae of the preleptocephalic stage, A. anagoides and A. shiroanago major had an elongated oil droplet on the ventral edge of the anterior part of the yolk sac, with the longest dimention more than 5 times the eye diameter of larvae one day old. The droplet disappeared by the time the larvae were 5 days old. Early larval-stage Gnathophis nystromi nystromi (Congridae) and Mystriophis porphyreus (Ophichthidae) had a few oil globules, as did fertilized developing eggs of these species. In the former specis, the oil globules had disappeared in larvae about 1 day old. Larva of the latter species had at least 20 oil globules at about 1 day of age, most of the oil globules were in the anterior part of the yolk sac. It is difficult to presume ditailes of the relationship between where oil globules are during oogenesis and where they are in fertilized eggs. When eggs still in the ovaries have a few small oil globules, they tended to have a few small oil globules after being fertilized. When eggs in ovaries had many oil globules moderate in size, they tended to have a single large oil globule and, less commonly a few small oil globules after being fertilized.

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Departmental Bulletin Paper

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