Studies on the reproductive rhythms of fishes. XVI. Environmental influences on testicular activity and related hormones in yarling goldfish.

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Ovaries of yearling female goldfish (comet variety) Carassius auratus exhibited little change under natural condition of summer. Gonadal maturation commenced from September and con-tinued till December. After an interruption in winter, it proceeded rapidly in March to culminate in spawning within a month. However, some fish remained immature.When transferred to 24°C/16L in summer, most females remained immature, but some matured and spawned after the transfer in later seasons. Females were suppressed after transfer to 24°C/12L in summer, autumn, and early winter, while some fish matured and spawned in late winter and spring. After transfer to 16°C in summer and autumn, however, most females matured to advanced stages regardless of photoperiod and some spawned in mid-winter.Plasma E2 level was high when the fish was maturing but low when the fish was immature. Plasma GtH levels were more dependent on the water temperature than on the gonadal maturation.