Studies on artificial control of reproductive cycle in fishes.

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1. The effects of water temperature and photoperiod on the reproductive activity were investigated in two fishes, freshwater cyprinid fish Honmoroko (Gnathopogon caerulescens) and seawater dragonet Tobinumeri (Repomucenus beniteguri), as new species. (1) Honmoroko showed a similar response with goldfish to environmental factors, that is, photoperiodism was dependent on temperature and high temperature suppressed gonadal maturation. Short daylength depressed maturation more effectively as water temperature increased. In autumn when temperature decreased, gonadal recrudescence started with the diminution of inhibitory effect of short daylength. Though maintenance of maturation needed long photoperiod in the spawning season of spring to early summer,high temperature in summer suppressed the gonadal activity when daylength was still long. (2) Tobinumeri began to spawn as temperature rose (above 18ﾟC) in spring, and stopped spawning temporally with further rise of temperature (above 28ﾟC). … More Spawning resumed with the fall of temperature in autumn (below 24-25ﾟC), and spawning continued below 14ﾟC. It was noticed experimentally that unlike honmoroko, long photoperiod had suppressive effect on gonadal activity in this fish.2. Rainbowtrout broodstock were reared under long photoperiods, 16L, 18L and 20L for about one year from March. Gonadal recrudescence advanced under long daylength, and at 16L females reached spawning peak in October whereas the peak of other groups were November. The spermiation of males of three groups started one month earlier than those of natural condition group. It was suggested that long photoperiod treatment can compensate the delay of male maturation which is a problem of many hatcheries where early spawning females have been selected.3 Two experiments were conducted with goldfish. One was long term exposure to 24ﾟC or 16ﾟC combined with 16L or 12L, and the other was short exposure to four regimes transferred from natural condition several times in a year. These experiments revealed that photoperiodism became clearer as temperature increased, but enhancement of gonadal maturation by long photoperiod was transient. It was also observed that high temperature and long photoperiod was suppressive to gonads in female but not in male.4. As to the plasma level of maturation related hormones in honmoroko and goldfish, estradiol-17beta of female fish and testosterone of male fish were correlated with degree of gonadal maturation but gonadotropin contents increased with the temperature regardless of maturational stage. Less