Spontaneous ovulation in goldfish is synchronized with photoperiod and influenced by water temperature and aquatic vegetation. As the latency to ovulation from injection of HCG is highly temperature dependent, the finding that ovulation occurs at approximately the same time of day at temperatures from 12' to 26" C suggests the time of the endogenous preovulatory gonadotropin surge may change with the temperature. The time of spontaneous ovulation adjusts to a reversed 1ight:dark cycle within 2 weeks; some 4-6 h shifts in a single 1ight:dark cycle modify the time ofovulation.Few sexually mature females kept under long photoperiod (16L8D) and transferred from cold (1 3 * I" C ) to warm (2 I 1" C ) water ovulated spontaneously. Exposure to artificial aquatic vegetation for as little as one light phase significantly increases the proportion of fish ovulating in warm water. Fish kept in cold water without vegetation do not ovulate; the addition of vegetation induces ovulation, although the response latency is longer than in warm water. Aquatic vegetation may be an effective stimulus for ovulation in other teleosts which spawn on this substrate.
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