The bambooleaf wrasse, Pseudolabrus sieboldi, is a diandric protogynous fish with a diurnal rhythm of ovarian development, and females spawn daily during the spawning season. This study investigated the steroidogenic pathway for estradiol-17β (E2) biosynthesis in vitellogenic ovarian follicles of the bambooleaf wrasse. We incubated follicles in vitro with radioactively labeled steroid precursors, and measured serum steroid levels using microtiter plate enzyme-linked immunosorbent assays (ELISAs). ELISAs for estrone (E1) and testosterone (T) were developed. The experiments showed that E2 was synthesized from pregnenolone via 17-hydroxypregnenolone, dehydroepiandrosterone, androstenedione, and E1. T was not produced from any radiolabeled precursors, and exogenous T was not converted to E2. During the spawning season, serum levels of E2 and E1 showed similar patterns, with a diurnal rhythm of high levels at 03:00 hr associated with active ovarian vitellogenic follicles. In contrast, serum T levels were constant and relatively low compared to levels of E2 and E1. These results indicate that E2 is synthesized via E1, rather than T, in the ovarian follicles, and suggest that T detected in the blood is likely derived from extra-follicular tissues.
All Science Journal Classification (ASJC) codes
- Animal Science and Zoology