Lunar synchronization of testicular development and steroidogenesis in rabbitfish
Md. Saydur Rahman, A. Takemura, K. Takano-2001
Comparative Biochemistry and Physiology -
Part B: Biochemistry and Molecular Biology, 129 (2-3):
367-373
(4th International Symposium on Fish Endocrinology)
Abstract:
Lunar synchronization of testicular development in
the golden rabbitfish, Siganus guttatus, was assessed by
measuring changes in sperm motility and conditions in the seminal plasma,
and by in vitro production of steroid hormones in testicular fragments and
sperm preparations. The duration and percentage of sperm motility was low 1
week before spawning (the new moon), but increased significantly on the day
of spawning (the first lunar quarter). During the first lunar quarter, the
osmolality decreased, but Ca2+ concentration increased in the
seminal plasma. These results suggest that spermiation occurs rapidly
towards the specific lunar phase. Testicular fragments and sperm
preparations were incubated with human chorionic gonadotropin (hCG) and two
precursor steroid hormones, 17a-hydroxyprogesterone
(17a-OHP) and testosterone (T), during the two
lunar phases. The production of 11-ketotestosterone (11-KT) increased
significantly when the testicular fragments were incubated with hCG at the
first lunar quarter, while incubation of sperm preparations with 17a-OHP during the same moon phase resulted in a
significant increase in 17a,20b-dihydroxy-4-pregnen-3-one (DHP) production in
the medium. These results suggest that 11-KT is produced in the somatic
cells of the testis under the influence of gonadotropin, and that sperm can
convert 17a-OHP
to DHP. Additionally, steroidogenic activity was considered to increase
toward the specific lunar phase. The synchronous increase in testicular
activity supports the hypothesis that lunar periodicity is a major factor
for the testicular development of S. guttatus.
(Sesoko Station, Tropical Biosphere Research Center,
University of the Ryukyus, 3422 Sesoko, Motobu, Okinawa 905-0227, Japan,
Tel.: +81-980-47-6215; fax: +81-980-47-4919, e-mail: tilapia@lab.u-ryukyu.ac.jp)