Studies on the reproductive rhythms of fishes. XIV. Annual reproductive cycle of 2-3 years old female goldfish and its artificial modification by manipulations of water temperature and photoperiod.

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Goldfish of the comet variety Carassrus auratus reared under natural conditions were trans-ferred to 24°C and 16°C combined with 12Land 16Lwith 1 to 2 month intervals, and maintained there for 1 to 2 months. Under natural conditions, most females started the regression by July. This stage was completed in August, then gonadal development commenced and continued till December. Vitellogenesis was blocked in winter, but resumed in late February. With rising temperature in March, gonadal maturation proceeded rapidly and resulted in spawning in about a month. Under 24°C/12L, females remained suppressed in summer, atutumn and early winter, whilesome fish matured and spawned in late winter and spring. Except during summer, 24°C/16L stimulated gonadal maturation which culminated in spawning during off seasons. At 16°C, regardless of photoperiod, the gonadal development was always accelerated, although the speed of gonadal maturation was slower than under 24°C/16L. Histologically, the liver cells as well as the gonadotrophs showed positive correlation with the ovarian activity, but the thyroid glands usually showed negative correlation with the ovarian activity.