Comparison of the effects of different methods of mammalian and salmon GnRHa administration on spawning performance in wild-caught female carp (Cyprinus carpio carpio) from the Caspian Sea

The effects of acute or sustained administration of mammalian and salmon GnRH agonists (mGnRHa and sGnRHa) were examined on the reproduction performance of wild-caught female carp from the Caspian Sea. Ripe broodfish were caught in the beginning of spawning season (early May) by seine from the southeast coastal waters of the Caspian Sea, Golestan province, Iran. To induce spawning fish were allocated into 8 groups and treated with 7% physiological saline (control), 4 mg kg− 1 carp pituitary (CP) extract (positive control), 20 μg kg− 1 mGnRHa or sGnRHa together with 40 mg kg− 1 Metoclopramide (acute treatments), a cholesterol pellet containing 20 μg kg− 1 mGnRHa or sGnRHa together with 40 mg kg− 1 Metoclopramide, and emulsified GnRHa in Freud's Incomplete Adjuvant (FIA) containing 20 μg kg− 1 mGnRHa or sGnRHa together with 40 mg kg− 1 Metoclopramide (mGnRHa-FIA and sGnRHa-FIA). After the final injection the fish were checked for spawning regularly. Ovulated fish were stripped manually and the eggs fertilized artificially. Significant differences were observed in the reproduction success, latency period and practical fecundity among treated groups (p ≤ 0.05). Injection of CP or sGnRHa in acute or sustained methods increased significantly the reproduction success compared to acute injection, implanting of mGnRHa or controls (p ≤ 0.05). In spite of the weaker effect of mGnRHa injection or cholesterol implant on induction of ovulation, treatment with mGnRHa-FIA showed similar effects as sGnRHa-FIA. Almost all sustained delivery systems of both GnRHa enhanced the practical fecundity of treated fish compared to CP and acute GnRHa injections. The latency periods of fish that received GnRHa-FIA and implant were near 24 and 50 h, respectively, which were significantly longer than that of fish given an acute GnRHa treatment or CP (p ≤ 0.05). There was no significant difference in fertilization and hatching success of the produced progeny among treated groups (p ≥ 0.05). The results showed that injection of GnRHa in FIA increased significantly the ovulation success of fish, but implanting fish with mGnRHa in a cholesterol pellet had variable effects with increasing fecundity but not higher ovulation success, compared to the CP treatment.