The effects of a single administration of [D-Ser(tBu)6,Pro9-NEt]-LHRHa at high dose alone (50 µg/kg), and at constant dose (20 µg/kg) combined with different doses of the dopamine receptor antagonist Metoclopramide (5, 10, 20, 40 mg/kg) for the induction of spawning in common carp broodstocks were determined under local hatchery conditions and compared with classic carp pituitary extract (CPE, double injection) application (water temperature 24 ºC). Fish injected with physiological saline (0.7% NaCl) were used as a control group. No spawning was observed in the control group or in the groups given LHRH-a combined with low (5, 10 mg/kg) doses of MET. The spawning ratio was low in the group given a high dose of LHRH-a alone (50 µg/kg), while it was high in the groups given LHRH-a combined with high (20, 40 mg/kg) doses of MET, and in the group injected with CPE. Latency period in the LHRH-a+MET groups was approximately half of that in the CPE group (14-16 and 24-26 h, respectively). There were no differences between spawned groups with respect to the spawning index of broodstocks, or the fertilization/hatching rate of eggs. It was concluded that spawning can be induced successfully in common carp broodstocks with 20 µg/kg LHRH-a+20 mg/kg MET, in a single injection, in a shorter latency period and without a negative effect on egg quality, compared to CPE treatment. This combination may be useful for more effective broodstock and hatchery management in common carp culture.

The effects of a single administration of [D-Ser(tBu)6,Pro9-NEt]-LHRHa at high dose alone (50 µg/kg), and at constant dose (20 µg/kg) combined with different doses of the dopamine receptor antagonist Metoclopramide (5, 10, 20, 40 mg/kg) for the induction of spawning in common carp broodstocks were determined under local hatchery conditions and compared with classic carp pituitary extract (CPE, double injection) application (water temperature 24 ºC). Fish injected with physiological saline (0.7% NaCl) were used as a control group. No spawning was observed in the control group or in the groups given LHRH-a combined with low (5, 10 mg/kg) doses of MET. The spawning ratio was low in the group given a high dose of LHRH-a alone (50 µg/kg), while it was high in the groups given LHRH-a combined with high (20, 40 mg/kg) doses of MET, and in the group injected with CPE. Latency period in the LHRH-a+MET groups was approximately half of that in the CPE group (14-16 and 24-26 h, respectively). There were no differences between spawned groups with respect to the spawning index of broodstocks, or the fertilization/hatching rate of eggs. It was concluded that spawning can be induced successfully in common carp broodstocks with 20 µg/kg LHRH-a+20 mg/kg MET, in a single injection, in a shorter latency period and without a negative effect on egg quality, compared to CPE treatment. This combination may be useful for more effective broodstock and hatchery management in common carp culture.