Studies on the reproductive rhythms of fishes - III. Environmental regulation of annual reproductive cycle in a spring-spawning bitterling Acheilognathus tabira.

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Abstract
Spring-spawning bitterling Acheilognathus tabira were kept under several combinations of photoperiod and water temperature regimes at different phases of their annual reproductive cycle. In early spring, the gonads developed rapidly under warm temperature (16°C) regardless of photo-period. In early summer, gonads intensely regressed under high temperature (26-30°C), also regardless of photoperiod. In early autumn, the first phase of gonadal recrudescence, i.e. forma-tion of spermatocytes and accumulation of yolk vesicles, proceeded under lower temperature (22°C-16L), regardless of photoperiod. In a mid autumn experiment, the second phase of gonadal recrudescencd, i.e. active spermatogenesis and accumulation of yolk globules, could be commenced only by warm temperature-long day (22°C-16L) treatment. Thus, it is concluded that the spawning period of A. tabira is initiated by the rising of water temperature in spring and is terminated by the high temperature in summer. The first phase of gonadal recrudescence is induced by the lowering temperature in autumn. In this season, how-ever, the second phase of gonadal recrudescence is prevented by the short daylength although the temperature is permissive. Seasonal changes in photoperiodism are also suggested.

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