The aim of the experiment was to identify the possibilities of stimulating pikeperch spawning with human chorionic gonadotropin (hCG) and Ovopel, a mammalian GnRH analogue (D-Ala⁶ Pro⁹ NEt-mGnRH) with a dopamine inhibitor (metoclopramide). Pikeperch spawners were caught with trap gear (fyke-nets) during the pre-spawning season from the Tałty and Tałtowisko lakes (Masurian Lakeland, northern Poland). After transport that lasted an hour, the fish were placed in tanks in a recirculating system and then segregated by sex. The females were divided into five experimental groups, each containing six specimens. The fish were injected twice at 24 hour intervals with hCG (group I - 200 and 200IU kg⁻¹ body weight (BW); group II - 200 and 500IU kg⁻¹ BW), Ovopel (group III - 0.25 and 0.50 pellets kg⁻¹ BW; group IV - 0.25 and 1.0 pellets kg⁻¹ BW) or 0.7% NaCl solution (group V, control - 0.2 and 0.5 cm³ kg⁻¹ BW). The effects of the hormonal stimulation expressed as the percentage of ovulating females, the degree of spawning synchronicity, and survival of the embryos to the eyed-egg stage were highly differentiated. The highest percentages of spent fish were obtained in the group stimulated with hCG - 83.3% (group I) and 100% (group II) of the females ovulated. The development of the oocytes in this group was rapid and synchronous, which was reflected in the shortened and relatively similar latency period (47 - 57 hours following the first injection; mean ≈ 51 hours) in individual females. No impact was noted with regard to hCG dose (400 vs. 700 IU kg⁻¹ BW) on the latency time or on egg quality. Ovopel did not positively affect either oocyte maturation or pikeperch ovulation. None of the fish from group III ovulated, and in group IV, as in the control group, eggs were obtained only from three (50%) females. In contrast to group V, the eggs of females stimulated with Ovopel were of low biological quality and survival to the eyed-egg stage ranged from 0 to 8%. Higher mortality among the females was also noted, especially in group III. The experiment indicated that hormonal stimulation with hCG is effective, while that with Ovopel was surprisingly ineffective.
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