Abstract
Plasma gonadotropin (GtH) and steroid hormone levels were monitored during ovulation in the common carp Cyprinus carpio. Nine out of 14 females ovulated after the water temperature was increased from 16 to 24°C. In the ovulated females, plasma GtH showed acute synchronous elevations in the afternoon around 1500 hours, peaked at midnight, and returned to the basal levels in the morning. Ovulationw as observed at midnight and early morning. Plasma 17α-hydroxy-progesterone and 17α, 20β-dihydroxy-4-pregnen-3-one fluctuated in phase with GtH. Only small changes were observed in the plasma E2 levels during ovulation. In most of the ovulated fish, testosterone distinctly increased with the commencement of temperature elevation and remained at high levels during the GtH surge, whereas in other ovulated fish only acute changes following the GtH surge were observed. In the unovulated females, large peaks of plasma GtH and steroid hormones were not observed. In some females, however, small rhythmical or irregular changes in GtH and/or steroid hormone levels were observed.
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