| Popis: |
Changes in serum steroid hormones were studied during the reproductive cycle of a viviparous rockfish, Sebastiscus marmoratus. Serum levels of estradiol-17β (E2) and testosterone (T) were moderately high throughout the spawning period from December until February (E2), and until post-spawning in April (T). Serum progesterone (prog) fluctuated but remained low throughout the annual reproductive cycle; 17α,20β-dihydroxy-4-pregnen-3-one (17α, 20β-diOHprog), on the other hand, was relatively high during the spawning period. During the spawning period, 7 of 12 females reared under laboratory conditions spawned twice at 10- to 16-day intervals. Histological observations indicated that oocytes developed gradually during gestation of the preceding brood and, after parturition, developed more quickly towards the end of vitellogenesis and subsequent fertilization. In repeat spawners, E2 and female-specific serum proteins remained high several days after the first parturition, then gradually decreased. Prog showed no significant changes over the period. The 17α, 20β-diOHprog, however, was low immediately after parturition, then rapidly increased, remained elevated during the middle of the period and then decreased. These results indicate that E2 is involved in vitellogenesis, and 17α, 20β-diOHprog may have some important roles in gestation in the multiple spawner S. marmoratus. |
