Northern pike (Esox lucius L.) is one of the fish species whose production in freshwater aquaculture may increase in the next few years. One method of producing this species is to create monosex stocks of pike, as females grow faster, mature later and gain larger body sizes. They can be obtained in the process of gynogenesis. The aim of this research was to determine and optimize the conditions of UV irradiating European perch (Perca fluviatilis L.) spermatozoa to inactivate them genetically (first experiment). The aim of this study was also to confirm whether perch spermatozoa can be used to induce northern pike gynogenesis using thermal shock (second experiment). During first experiment the highest rate of haploid larvae (29.9 ± 0.85%) was noted in the group inseminated with perch sperm irradiated for 6 min (1548 J m-2). No viable embryos were observed in groups of eggs inseminated with sperm irradiated for more than 10 minutes (2580 J m-2). The heat shock applied 12 or 14 min after gamete activation, for 3 or 5 min at 34.0°C, resulted in obtaining of gynogenetic specimen due to retention of the second polar body in all experimental groups. The most efficient was heat shock applied 14 min after gamete activation and lasting 3 min, and resulted in 18.5 ± 1.3% of gynogenetic larvae for female B. Heat shock applied 12 min after gamete activation, lasting 3 min was also effective in the case of female A, resulting in obtaining of 16.5 ± 2.1% gynogenetic specimen.
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