Multiple spawning in amphidromous ayu, Plecoglossus altivelis altivelis [Clupeoidei], from Hokkaido, Japan
1991
Sakai, H. (Hokkaido Univ., Hakodate (Japan). Faculty of Fisheries) | Katsura, K. | Hirata, T. | Goto, A.
The possibility that female amphidromous Ayu, Plecoglossus altivelis altivelis, from Hokkaido spawn twice per season was investigated by histological observations of ovaries of 29 females caught from the Mogusa River of southern Hokkaido during the spawning period from August to October in 1984. Of those fish examined, 12 out of 16 individuals which had empty follicles in their ovaries were attaining their second maturation. No individuals were caught whose ovary eggs were all in a state of degeneration. Therefore, it was presumed that a large part of the population spawns twice per spawning season. Ayu in the Mogusa River and landlocked ayu in Lake Biwa share some similar reproductive characters such as multiple spawning and small-sized eggs. Their similarity is thought to result from an adaptive convergence of their reproductive manner. Under unfavorable environmental conditions, both populations of Ayu must compensate for their insufficient number of eggs per batch by attempting to spawn twice
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