HORMONAL INDUCTION AND SYNCHRONIZATION OF OVULATION IN ENDANGERED CASPIAN BROWN TROUT (SALMO TRUTTA CASPIUS KESSLER, 1877) AND ITS EFFECTS ON EGG QUALITY

The aim of this study was to evaluate the effects of different hormones to induce and synchronizing of ovulation in an early spawning of Salmo trutta caspius. Fish were selected in the beginning of the spawning season and were allocated into five groups and were treated intraperitoneally; (I) 0.5 ml of sGnRHa in two injections (GnRHa–Dom, GnRH-1), (II) 0.5 ml propylene glycol-dissolved mGnRHa in two injections (GnRHa–Met, GnRHa-2), (III) 0.5 ml propylene glycol-dissolved [D-Trp6-mGnRH] in two injections (GnRHa–Met, GnRHa-3) and (IV) 0.5 ml propylene glycol-dissolved sGnRHa in two injections (GnRHa– Met, GnRHa-4) and (V) 0.5 ml propylene glycol in two injections (control group). The GnRHa and dopamine antagonist doses in all hormone treatments were 20 μg kg-1 and 10 mg kg-1 body weight respectively. In each injection, fish received half dose of hormone. All treatment groups received two injections four days apart. All fish in treatment I & II groups had 100% ovulated within 15 & 14 days after treatment, respectively. While 50% and 83.33% of the fish in the treatment III & IV ovulated within 18 to 21 days after treatment respectively. The control group had only 33.3 % after 31 days. Fish injected with the GnRHa had a mean time ovulation of 13 days, compared with 24 days for control treated fish. None of the treatments caused any pre- or post-spawning mortality in the broodstock. Fertilization, eyeing and hatching percentages of the produced progeny were normal in all the treatment groups and did not differ significantly among them (p>0.05). In conclusion, all GnRHa-DA treatments were effective in advancing the onset of ovulation, synchronizing the ovulation of the treated fish and shortening the egg collection period, relative to the control without affecting broodstock survival and egg quality.