Factors involved in the development of and decline in photoperiodism as it relates to the gonadal activity of a spring-spawning bitterling,Acheilognathus tabira
✍ Scribed by Shimizu, Akio ;Hanyu, Isao
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 750 KB
- Volume
- 265
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
The involvement of changes in photoperiodism in gonadal activity was investigated in the spring‐spawning bitterling, Acheilognathus tabira, in which photoperiodism develops during the summer and declines during the winter. In spring, gonadal development occurred without a need for photoperiodic stimulation and independently of the preceding photoperiod (9 hours or 12 hours light; 9L or 12L) during the winter. This observation indicates that the natural photoperiod during the corresponding season is not responsible for the decline in photoperiodism. Fish kept at moderate temperatures (16°C or 22°C) during the winter eventually achieved gonadal maturation, even under short daylength conditions (11L), indicating that low temperature during the winter is not necessary for the decline in photoperiodism. Both treatment with moderate temperature and long days (22°C, 15L) treatment and treatment with moderate temperature and short days (22°C, 11L) induced the development of photoperiodism during the summer, an indication that neither high temperatures during the summer nor long days during the early summer are necessary for the development of photoperiodism in this species. Since the natural photoperiod and temperature conditions during the corresponding seasons are not responsible for the changes in photoperiodism, these changes are probably caused by an internal factor such as circannual rhythm.
Alteration of the photoperiodic regime from 11L to even fewer hours of daylight during the period when photoperiodism was declining did not affect subsequent gonadal development. The nature of the changes in photoperiodism in this species is, therefore, a rapid switchover of the responsiveness to daylength rather than a gradual change in the critical daylength for gonadal development. © 1993 Wiley‐Liss, Inc.