Endocrine and morphological correlates of reproduction in the draughtboard shark Cephaloscyllium laticeps (Elasmobranchii: Scyliorhinidae).

This study examined the endocrine and reproductive correlates of reproduction in 636 female and 468 male draughtboard sharks (Cephaloscyllium laticeps) captured from southeastern Australia. Females were oviparous and displayed a single external-type ovary with a maximum follicle diameter of 35 mm. Vitellogenesis commenced at a follicle diameter of 10 mm. Females showed a constant overlap between follicular recruitment, ovarian growth, and egg laying. The male reproductive tract consisted of paired testes with spermatocysts undergoing diametric development. Plasma levels of the presumptive gonadal steroids, testosterone (T), 17beta-estradiol (E2), progesterone (P4), and 11-ketotestosterone (11-KT; males only) were correlated with morphological developmental stages of the gonads. In females, E2 increased as the follicle developed before declining as the follicle reached maturity. T remained low during the first stages of ovarian growth and increased as the follicle reached maturity. P4 showed a peak just before ovulation. In males, T was the only hormone that varied with maturity, increasing in adults; E2 and P4 were present at low plasma concentrations in males and did not change with stage of gonadal development. 11-KT was undetectable at all times. Endocrine changes in draughtboard sharks were consistent with hormonal correlates reported for other species and suggest roles for E2( in females) and T (in both sexes) in gametogenesis and P4 in maturational events in females.

Effects of aromatase inhibitors on in vitro steroidogenesis by Atlantic salmon (Salmo salar) gonadal and brain tissue.

In order to assess the efficacy of selected aromatase inhibitors on Atlantic salmon (Salmo salar) ovarian and brain tissue, in vitro systems were developed for measuring 17beta-estradiol (E(2)) production by these tissues. Isolated vitellogenic follicles, or homogenised whole brains were incubated at 10 degrees C in complete Cortlands solution for 18 or 42 h respectively, and E(2) levels in the medium were determined by RIA. The addition of testosterone to the medium increased E(2) production in all preparations. E(2) production by whole brain homogenate was reduced by co-incubation with the aromatase inhibitors 1,4,6-androstatriene-3,17-dione (ATD), 4-androstene-4-ol-3,17-dione (OHA), aminoglutethimide, fadrozole or miconazole. Fadrozole, ATD, and OHA reduced E(2) production by vitellogenic follicles at a medium concentration of 0.1 microg mL(-1), whereas miconazole was only effective at 10 microg mL(-1). This study demonstrates a simple and rapid screening method for assessing the efficacy of aromatase inhibitors on fish tissues, and that the aromatase inhibitors ATD, OHA and fadrozole are potent inhibitors of both brain and gonadal aromatase in vitro, in Atlantic salmon.

Maintenance of Atlantic salmon (Salmo salar) at elevated temperature inhibits cytochrome P450 aromatase activity in isolated ovarian follicles.

Atlantic salmon (Salmo salar) broodstock were transferred from natural (12-16 degrees C) to controlled temperatures of 14, 18 or 22 degrees C for 3 months during vitellogenesis. Fertility and survival were significantly reduced in eggs from broodstock held at 22 degrees C relative to 14 or 18 degrees C. Endocrine mechanisms were disrupted after only one month at 22 degrees C, as evidenced by decreased plasma vitellogenin (Vtg) and increased plasma testosterone (T) levels and, at later stages, decreased levels of plasma 17beta-estradiol (E2). In vitro incubations of isolated ovarian follicles were carried out at monthly intervals, with follicles exposed to human chorionic gonadotropin, N-2-0-dibutyryladenosine 3,5-cyclic monophosphate, and the gonadal steroid precursors 17-hydroxyprogesterone, androstenedione, and T. After one month of exposure to controlled temperature, T synthesis was generally enhanced in response to all treatments at all temperatures, but E2 synthesis was inhibited at 22 degrees C, suggesting temperature impairment of cytochrome P450 aromatase (P450arom) synthesis or activity. The effect became less marked as follicles matured suggesting that temperature sensitivity is stage dependent. The results of this study suggest that the inhibitory effects of elevated temperature on E2 and Vtg synthesis, and subsequent egg development found in the present and earlier studies, arise at least partly, from temperature modulation of P450arom.