Introduction
The development of protocols for photothermal spawning induction in pikeperch has been a subject of interest for both scientific and commercial purposes during the last few decades (Hermelink et al., 2011; Żarski et al., 2019; Ljubobratović et al., 2025 ). Accordingly, several protocols have been published, showing their applicability on different levels of reproductive biology indicators. Nevertheless, the advanced gametogenesis cannot guarantee high reproductive performance, which is especially so in the case of eggs, where late stimulation of ovulation may lead to a reduction in gamete quality (Ljubobratović et al., 2022 ). Therefore, the evaluation of different scenarios of protocols for induction of out-of-season induction and their effect on egg quality upon hormonal stimulation is of importance for establishing indicators of the appropriate maturation stage for the procedure of artificial reproduction.
Materials and methods
The study was conducted in one climate chamber over two consecutive years in period from December 2020 to November 2022. In this manner, two pho to-thermal spawning protocols were applied: SHORT - 19-week-long, composed of cooling only ; LONG - 23-week-long, composed of 19 weeks of cooling with an additional four weeks of chilling. Accordingly, the first reproduction took place in early October 2021, while the second one was performed in early November 2022. For both reproductions, the warming thermal protocol of the artificial reproduction was conducted (Ljubobratović et al., 2021). The SHORT group was composed of 18 pairs of breeders, while the LONG group was composed of 15 pairs of breeders. The ovarian follicle diameter was measured three times during the cooling and chilling period, and egg and sperm quality were examined during the artificial reproduction.
Results
Significantly higher ovarian follicle diameters were found at each sampling moment in the LONG group. Latency time was significantly shorter in LONG groups, while main egg quality features were better in the SHORT group, except pseudo-gonadosomatic index, which was higher in the LONG group. On the other hand, better sperm quality was observed in the LONG group.
Discussion
Based on the assessed results, it seems that the final chilling phase, composed of a stable minimal temperature, is not required in case of artificial reproduction using external hormones for ovulation stimulation. While this phase appears beneficial for males, it may lead to latency time reduction and, consequently, to egg quality deterioration. Future studies should evaluate whether the low temperatures are necessary for out-of-season artificial reproduction.
Acknowledgements
The study was funded by the National Research, Development and Innovation Fund of Hungary (grants PD139053, K138425, FK142933). This work was supported by the Research Excellence Programme and by the Flagship Research Group Programme of the Hungarian University of Agriculture and Life Sciences. The corresponding author was granted the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.
Reference
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