Development of a homologous radioimmunoassay for red seabream follicle stimulating hormone and regulation of gonadotropins by GnRH in red seabream, Pagrus major

Effect of GnRHa on plasma levels of Fsh and Lh in the female greater amberjack Seriola dumerili

“…In the plasma of adult female tilapia Oreochromis niloticus (L. 1758), Fsh concentrations increased 6 h after a single injection of an analogue of salmon GnRH (GnRH3; Trp 7 , Leu 8 GnRH) (Aizen et al ., ). However, in adult male red seabream Pagrus major (Temminck & Schlegel 1843), plasma Fsh levels did not rise between 2 and 24 h post‐injection of GnRHa (Okuzawa et al ., ). In the present study, GnRHa implants did not elevate plasma levels of Fsh in the post‐vitellogenic female greater amberjack within 42 h of GnRHa administration, suggesting that short‐term administration of GnRHa does not stimulate Fsh release in this species either.…”

“…In the present study, GnRHa implants did not elevate plasma levels of Fsh in the post‐vitellogenic female greater amberjack within 42 h of GnRHa administration, suggesting that short‐term administration of GnRHa does not stimulate Fsh release in this species either. Additionally, implantation of GnRHa cholesterol pellets did not stimulate Fsh release in juvenile or adult red seabream (Okuzawa et al ., ). Additional experiments are necessary to determine if GnRHa does not stimulate Fsh release even in juvenile or previtellogenic female greater amberjack.…”

“…GnRHa administration has been demonstrated to stimulate Lh release in a range of species (Mylonas & Zohar, ; Rosenfeld et al ., ), including tilapia (Aizen et al ., ) and red seabream (Okuzawa et al ., ). Similarly, the present study showed that GnRHa implants elevated plasma levels of Lh in the female greater amberjack, suggesting that elevated plasma Lh triggered OM, resulting in ovulation.…”

“…Previous studies on adult fish have demonstrated that circulating Gth concentrations increased within 24 h of GnRHa administration (Aizen et al ., ; Okuzawa et al ., ). Hence, the present study focused on the short period of GnRHa stimulation on Gth release, from the GnRHa implant to the first ovulation.…”

“…At present, Fsh and Lh assays are available only for limited fish species. With the exception of salmonids, where Fsh and Lh assays have been available since the late 1980s (Suzuki et al, 1988;Swanson et al, 1989), assays for other species, especially the Fsh assay, have been developed only since 2000 (Aizen et al, 2007b;Kazeto et al, 2019;Okuzawa et al, 2016). Hence, the effect of GnRH upon the release of Fsh and Lh in many fish species remains to be explored.…”