Correlation between plasma steroid hormones and vitellogenin profiles and lunar periodicity in the female golden rabbitfish, Siganus guttatus (Bloch)

Characteristics of the lunar reproductive cycle in the golden rabbitfish, S iganus guttatus, were determined by histological observations of ovarian de velopment, and immunological measurements of plasma steroid hormones, estra diol-17 beta (E-2), testosterone (T), 17 alpha,20 beta-dihydroxy-3-pregnen- 3-one (DHP) and 17 alpha,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta-S), and vitellogenin (VTG). Ovarian and plasma samples were collected every we ek according to the lunar phases from May to July. Weekly change of gonados omatic index (CSI) showed two peaks at the first lunar quarter in June and July. Yolky oocytes were also observed around this time. Histological obser vations revealed that the vitellogenic oocytes appeared again 1 week after spawning and developed synchronously. These results suggest that this speci es is a multiple spawner and the oocyte development is in a group-synchrono us manner. Plasma steroid hormones (E-2, T, DHP and 20 beta-S) and VTG leve ls changed in parallel with changes in GSI. The peak of plasma VTG level oc curred prior. to spawning. These cyclic changes of plasma steroid hormones and VTG support the hypothesis that lunar periodicity is the major factor i n stimulating reproductive activity of S. guttatus. (C) 2000 Elsevier Scien ce Inc. All rights reserved.