Effect of luteinising hormone-releasing hormone analogue and human chorionic gonadotropin on ovulation, plasma and ovarian levels of gonadal steroidsin greenback flounder Rhombosolea tapirina

Female greenback flounder Rhombosolea tapirina were treated with either des Gly(10) [D-Ala(6)] LHRH ethylamide (LHRH-a) at 50 or 100 mu g/kg intraperi toneal injection (ipi), LHRH-a cholesterol pellet (LNRH-a pellet) 100 mu g/ kg implanted intraperitoneally, or human chorionic gonadotropin (hCG) 1,000 IU/kg ipi, Treatment with hCG, LHRH-a (50 mu g/kg) ipi and LHRH-a pellet i ncreased the total number of ovulations above control levels. LHRH-a (100 m u g/kg) ipi was not consistently more effective than the control and both L HRH-a (50 mu g/kg) ipi and LHRH-a pellet induced more ovulations than LHRH- a (100 mu g/kg) ipi. Of those fish that ovulated, most ovulated more than t wice, and most ovulations occurred at daily intervals. Oocyte diameters inc reased and oocyte stage advanced significantly in response to all exogenous hormone treatments. This was accompanied by increases in plasma and ovaria n levels of 17 beta-estradiol (E-2), and in most cases, plasma and ovarian levels of testosterone (T). Plasma and ovarian levels of 17,20 beta-dihydro xy-4-pregnen-3-one (17,20 beta P) were not consistently elevated in associa tion with reproductive events.