Effects of several methods of GnRHa administration on induction and synchronization of ovulation in rainbow rout, Oncorhynchus mykis

Subject Areas : New Technologies in Aquaculture Development

Received: 2020-11-02 Accepted : 2020-11-02 Published : 2008-11-21

Keywords: Rainbow trout, egg quality, GnRHa, Keywords: Freund’s incomplete adjuvant, Induced spawning,

Abstract :

Abstract In this study likely effects of water in oil (w/o) emulsion versus acute administration of gonadotropin releasing hormone agonist (GnRHa) on induction and synchronization of ovulation in rainbow trout were examined. GnRHa was diluted in physiological saline (PS) or propylene glycol (PG) and mixed with equal volume of Freund’s incomplete adjuvant (GnRHa-FIA). All fish received 0.5 ml intraperitoneal injections. Dose of hormone in all groups was 25 μg/kg-1 except control fish which received physiological saline. All fish injected with PS diluted GnRHa, combined with adjuvant or in two injections protocol ovulated 10 and 11 days after injection respectively. In contrast only 75% in control fish and 60% of fish with an acute injection of pure GnRHa ovulated up to 36 days after injection. In fish injected with PG diluted GnRHa combined with adjuvant ovulation percentage reached to 87% until the end of experiment compared to 100 % ovulation for fish injected twice with PG diluted GnRHa. Fertilization, eyeing and hatching percentages were normal in all treatment groups and did not differ significantly among groups (p >0.05). None of treatments caused any pre or post-spawning mortality. In conclusion, combination of physiological diluted GnRHa with Freund’s incomplete adjuvant (GnRHa-FIA) was effective in advancing the onset of ovulation, synchronizing the ovulation of treated fish and shortening the reproductive period, relative to control or acute GnRHa injected group (p <0.05). GnRHa-FIA did not affect egg quality or cause any mortality in the treated broodstock.