Introduction
Percids are coolwater species, and while thermophilic in terms of growth they require a cold period for reproduction (Embrke et al., 2025). While pikeperch (Sander lucioperca) requires cooling for maturation of its gonads, it is yet speculative what the lowest temperature is required for its successful reproduction (Hokanson et al., 1977). Thus far, there have been two studies evaluating this topic (Hermelink et al., 2017; Milla et al., 2021). Although both studies showed that a relatively high temperature of 12 °C was appropriate for full gonadogenesis, fish reproduction was not reported, so the gamete quality was not assessed. Accordingly, to the best of our knowledge, the study that reported reproduction with the warmest wintering temperature was at about 9 °C (Ljubobratovi�� et al., 2020). On the other hand, the study that reported the lowest temperature for the successful reproduction was at 10 °C (Ljubobratovi�� et al., 2021). Building upon the previous knowledge, yet aiming to reach a feasible spawning induction protocol, the present study evaluated the egg quality in two batches of females with different reproductive experience when the chilling phase was performed at 10 °C.
Materials and methods
In total, 20 females were used for the evaluation of the egg quality. Prior to induction in fully controlled conditions, fish were raised outdoors in in-pond raceways for three years, when the spawning cycle shift was performed (Ljubobratovi�� et al., 2025). Ten females were seven years old and had already been artificially reproduced twice since the cycle shift (OLD), while the other ten were five years old and had not been artificially reproduced thus far, and had just been submitted to the reproductive cycle shift for the study (YOUNG). Mimicked summer was performed at a stable temperature of 21 °C with constant daylight reduction of 2 min/day from 15.5h to 12h. Autumn was mimicked with gradual cooling from 21 °C to 10 °C at a rate of 1°C weekly, while the daylight period was further reduced to a minimal 8.8h with stable dynamics of 2 min daily. Further on, the stable 10 °C was kept, while the daylight increased with a dynamic of 3 min/day. Upon one (EARLY) or two months (LATE) of this stable chilling phase, ten fish (five from each class) were hormonally stimulated and reproduced by the stable thermal protocol described by Ljubobratovi�� et al. (2021). In short, from hormonal stimulation until the GVBD, the temperature was kept at 10 °C, while upon reaching the germinal vesicle breakdown, the fish was moved to 12 °C until ovulation, which took place within 24 h.
Results
Latency time was affected by both induction moment and the age of the breeders, being on average 2 days and 4.5 days shorter in YOUNG, for EARLY and LATE reproduction batches, respectively. Embryo survival rate was relatively high in both batches, with a mean about 10 % higher in the EARLY batch and ranging from 31.4 % to 78.8 % and from 49.3 % to 87.0%, in the EARLY and LATE batches. Embryo survival was not affected by either of the two assessed factors. Oil globule fragmentation was affected by the induction duration only, being higher in the LATE batch (24.2 ± 37.5 % vs. 2.7 ± 4.8 %).
Discussion
The present results show that pikeperch's ability to produce high-quality eggs upon hormonal stimulation of ovulation, even with the chilling phase being at 10 °C, yet offering a one-month period of propagation similar to earlier reports at lower temperatures (Ljubobratovi�� et al., 2020). Based on the assessed egg quality features, it appears that even after the repeated cycles in the shifted reproduction regime, females are still capable of yielding high reproductive performance, ensuring the reliability of the protocol. The presented spawning induction schedule, following the reproduction cycle shift, presents a new step forward towards the economic feasibility of pikeperch off-season egg supply.
Acknowledgements
This research was funded by the National Research, Development and Innovation Fund of Hungary (grants PD-139053 and K138425) and by the Flagship Research Group Programme of the Hungarian University of Agriculture and Life Sciences. The presenting author was granted the J��nos Bolyai Research Scholarship of the Hungarian Academy of Sciences.
Reference
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