Regulation of Reproductive and Metabolic Indices by the Interaction of Daily Environmental Stimuli in the Gulf Killifish, Fundulus Grandis.

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Doctor of Philosophy (PhD)


Section I. Gonad weights and body fat stores of male Gulf killifish, Fundulus grandis, are stimulated or inhibited by timed daily disturbances by netting for two-three weeks as a function of the time of day when netting is done. In addition, the phases, amplitudes and patterns of the gonadal and fat response rhythms may be influenced by daylength and season. In one test in February-March, the gonadal response rhythm was similar in fish held on LD 12:12 at two water temperatures (20(DEGREES) and 28(DEGREES)C), with a peak occurring at 8, and a trough at 16 hours after light onset. In fish held at 20(DEGREES)C during May, the peak of the gonadal response rhythm to netting occurred at 12 hours after light onset on LD 12:12 and LD 10:14, but no rhythm was evident on LD 14:10. In another test in fall, the fat response rhythm appeared to recycle in fish held on a 48-hour day (LD 12:36) with a 20-hour perod so that similar responses to netting disturbance occurred at 0, 20 and 40 hours after light onset and all other times separated by 20 hours. These results indicate that the daily photoperiod entrains a circadian rhythm of responsiveness to physical disturbance that is similar to photoperiodism in which the daily photoperiod entrains a circadian rhythm of responsiveness to light. Section II. Male Gulf killifish, fundulus grandis, were held on photoperiodic and thermoperiodic regimens for 2 to 4 weeks and examined with respect to body fat stores and testes weights. Groups of fish kept on a 24-hour (LD 12:12) photoperiodic regimen in spring were provided a water temperature of 28(DEGREES)C except for a 4-hour daily cryophase of 20(DEGREES)C given at one of six different times during the photocycle. Cold pulses were stimulatory for the GSI at most times of day, but not when they were initiated at four hours after light onset. Similarly, fish kept on a 48-hour (LD 12:36) photocycle and 28-30(DEGREES)C during fall were provided a 4-hour cryophase of 20(DEGREES)C once during each photocycle in various phase relations to the photoperiodic regimen. Reciprocally, some groups were held at 20(DEGREES)C and provided a 4-hour thermophase of 28-30(DEGREES)C. The fat response rhythm of the groups receiving the cryophase was similar in pattern to that of the groups receiving the thermophase. This suggests that the temperature change in itself, rather than the direction of the temperature change, is the significant cue. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.





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