Abstract
The mechanisms underlying the photoperiodic entrainment of the endogenous circannual rhythm of maturation in the rainbow trout were investigated by subjecting December-spawning fish to abrupt changes in daylength which varied in their timing or magnitude. These protocols advanced spawning by up to 4 months. Maturation occurred in sequence in fish maintained on 18L:6D from January and February, and in fish exposed to 18L:6D from December, January and February, followed by 6L:18D in May, indicating that the abrupt increases in daylength were effective entraining cues. `Long' photoperiods of between 12 and 22 h applied in January, followed by shorter photoperiods of between 3.5 and 13.5 h from May, were equally effective in advancing maturation. Maturation was also advanced, though to a lesser extent, in fish maintained on photoperiods of 8.5 or 10 h from January, followed by a photoperiod of 1.5 h from May. In contrast, maturation was delayed in fish maintained under a constant 8.5-h photoperiod from January, and these fish also exhibited a desynchronization of spawning times characteristic of endogenous circannual rhythms in free-run. Collectively, these results indicate that photoperiodic history determines the reproductive response of rainbow trout to changes in daylength.
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Accepted: 7 August 1998
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Randall, C., Bromage, N. Photoperiodic history determines the reproductive response of rainbow trout to changes in daylength. J Comp Physiol A 183, 651–660 (1998). https://doi.org/10.1007/s003590050288
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DOI: https://doi.org/10.1007/s003590050288