Effect of gonadotropin-releasing hormone analogue (GnRHa) and pimozide on plasma levels of sex steroids and ovarian development in sea bass (Dicentrarchus labrax L.)

To synchronise and advance spawning, European sea bass females in late vite llogenesis were treated with two i.p. injections of GnRH analogue alone (5 and 20 mug/kg BW) given 12 h apart, or combined with pimozide (PIM) (10 mg/ kg BW) either in the first or second injection. Saline-injected and untreat ed females were used as controls. Administration of GnRHa alone or combined with PIM accelerated the final oocyte maturation (FOM) and induced spawnin g. However, 48 h after the second injection the size of oocytes and the per centage of oocytes in GVBD stage were lower in the PIM-treated females. The number of eggs spawned was highest in the group that received GnRHa alone and lowest in the group that received PIM in the second injection. Plasma l evels of 17 beta -oestradiol (E2) increased sharply at 12 h after the first injection of GnRHa alone or combined with PIM, decreasing after a second i njection of GnRHa alone. However, the plasma E2 decreases was much slower i n females that received the PIM in the first injection. Females that receiv ed PIM in the second injection still showed elevated plasma E2 during a lon ger period. Plasma testosterone (T) increase was parallel to the plasma E2 decrease and peaked earlier in the group that received GnRHa alone in both injections. Low and nonsignificant changes of 17 alpha ,20 beta -dihydroxy- 4-pregen-3-one (17,20 beta -P) were observed in plasma during the time that the animals were sampled. The results demonstrate that the use of PIM does not improve the GnRHa treatment and the use of GnRHa alone during the last stages of vitellogenesis is enough to induce FOM in the European sea bass. (C) 2001 Elsevier Science B.V. All rights reserved.