Spawning induction in common carp ( Cyprinus carpio) using pituitary extract or GnRH superactive analogue combined with metoclopramide: analysis of hormone profile, progress of oocyte maturation and dependence on temperature

Abstract

Spawning experiments under routine hatchery conditions on Israeli farms showed that successful ovulation in the common carp (Dor 70×Yugoslavian lines) can be achieved by a single administration of 10 μg/kg sGnRHa ([D-Arg 6,Pro 9-NEt]-sGnRH) combined with 20 mg/kg of the water-soluble dopamine receptor antagonist, metoclopramide (GnRH + MET). An initial rise in the maturational gonadotropin (cGtH) level occurred 3 h after treatment, gradually increasing thereafter, and reaching a peak of 227±41.8 ng/ml (mean ± s.e.m., n = 10) 14 h after treatment, when full ovulation took place, as reflected by the presence of a few expelled eggs on the bottom of the tank. This rise was associated with increased levels of oestradiol-17 β (E 2; 19.5 ± 3.4 ng/ml) and 17 α,20 β-dihydroxy-4-pregnen-3-one (17,20-P; 23.9±19.7 ng/ml). Ovarian biopsies showed a gradual progress in oocyte maturation with germinal vesicle breakdown (GVBD) occurring during the rise in both steroids. At the time of initial egg release, GtH remained at a high level while the steroids started to decline. In a parallel group, fish were primed with a dose of carp pituitary extract (CPE), calibrated to contain 0.07 mg/kg cGtH, and 11 h later with a resolving dose of CPE (0.34 mg/kg cGtH). Following priming, circulating GtH and E 2 increased moderately, and the germinal vesicle migrated towards the oocytes' periphery. A further increase in cGtH and E 2, and a sharp peak in 17,20-P, occurred concomitantly with GVBD, 6 h after the resolving dose was given. Data compiled from several spawning experiments showed that the interval between hormone administration and initial egg release (latency) was negatively correlated with water temperature over the range of 20–26°C. While latency was always longer in GnRH+MET than in CPE treatment, in each treatment it was nonetheless constant between 22.5°C and 25°C. GnRH+MET given at various hours of the day or evening resulted in identical spawning with the same latency. This fact, together with the predicted latency at a given temperature, may provide the aquaculturist with a protocol to accurately schedule spawning induction in the common carp.