Secretion of progestogens during induced ovulation in goldfish

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Abstract
Female goldfish (Carassius auratus L.) were held at 20 °C and ovulation was induced by injection of des-Gly10[D-Ala6] luteinizing hormone releasing hormone ethylamide (LHRH-A) plus pimozide, and 3 h later, LHRH-A. This treatment causes rapid onset of a prolonged surge of gonadotropin (GtH) release. At 6 h after the second set of injections, serum levels of GtH, 17α-hydroxyprogesterone (17α-P), and 17α-hydroxy-20β-dihydroprogesterone (17α,20β-P) are significantly higher than in control groups; oocytes have reached the germinal vesicle breakdown stage of maturation by this time. By 20 h after the second set of injections, seven of eight fish had ovulated in the LHRH-A and pimozide treatment group; the serum levels of GtH were greater than at 6 h, but serum concentrations of 17α-P and 17α,20β-P were decreased to control levels. The ovulated fish still retained ovulated oocytes. This indicates that goldfish have a preovulatory surge of secretion of progestogens, which may aid in induction of oocyte maturation and ovulation within a short time period, enabling the goldfish to synchronize ovulation with the photoperiod and to take advantage of favorable environmental conditions for spawning within a 24-h period.