Studies on the reproductive rhythms of fishes. XV. Environmental influences on ovarian acitivty and related hormones in yearling goldfish.

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Under natural condition, yearling male goldfish Carassius auratus started regression by late July and completed in August. Then gonadal development commenced and proceeded to milting by October. Spermatogenesis was arrested in winter. However, milting fish appeared again in March. When transferred to 24°C, the male fish matured within a short period at both 12L and 16L in off breeding seasons. However, the minimum time needed for reaching milting was shorter at 16L than at 12L. On both regimes, the spawning stage did not last long but passed to the post-spawning stage. Conversely, males matured and stayed in milting condition at 16°C regardless of photoperiod. The speed of maturation was slower at 16°C than at 24°C regimes. Plasma testosterone levels were high when the fish was maturing or matured but low in immature fish. Plasma gonadotropin levels were more dependent on the water temperature than on the maturation stages. Plasma thyroxine levels did not show clear relationship to the testicular activity at both 16°C and 24°C regimes.