Advancement and synchronisation of spawning in Salmo gairdneri and S. trutta following administration of LRH-A combined or not with pimozide

Abstract

Abstract Prior to the onset of the spawning season female rainbow trout were injected intraperitoneally (IP) with LRH-A ([des Gly 10 D-Ala 6 ] LHRH ethylamide) alone at a dose of 1 μg/kg body weight or in combination with pimozide (PIM, 10 mg/kg body weight), a dopamine antagonist, given 6 h before the LRH-A. Pimozide + LRH-A and pimozide alone induced a significant elevation in plasma GTH but only PIM + LRH-A consistently advanded ovulation. Egg quality was altered with PIM + LRH-A and PIM + saline, resulting in lower survival at the eyed stage. Prior to the onset of the spawning period, brown trout were injected IP with LRH-A alone at doses of 1, 10 and 20 μg/kg body weight. A single injection slightly initiated and synchronized ovulation at doses of 10 and 20 μg; a second injection given 6 days later did not modify the ovulation profile. There was no effect when the same doses were given in pelleted form in silicone rubber implants. When LRH-A and PIM were injected IP 6 h apart at doses of 10 and 1 mg/kg body weight PIM and 10 μg/kg body weight LRH-A, ovulation was slightly stimulated. The effects of LRH-A given in silicone rubber implants were potentiated by simultaneous injection of PIM (10 mg/kg body weight). No alteration of egg quality was observed after these various treatments on brown trout.