The main problem of artificial reproduction of pikeperch presents the unpredictability of the latency time (LT) (Żarski, et al., 2019) . Therefore, a special final oocyte maturation (FOM) classification was developed in order to tackle this (Żarski et al., 2012). Although useful, this procedure still requires frequent handling especially in cases of out-of-season reproduction when the fish are commonly hormonally stimulated in the first stage of FOM. A recent paper showed high agreements in the post-stimulation maturation dynamics in pikeperch between in vivo and in vitro oocyte maturation (Ljubobratović et al., 2023). Therefore, using the in vitro maturation (IVM) technique, we are aiming at developing a method that predicts the individual latency time and thus minimizing the number of handling procedures that require the biopsy of oocytes.
Materials and methods
In early November 2022, during out-of-season pikeperch reproduction, in total 13 females were hormonally stimulated with salmon gonadoliberin analog using the warming thermal regime (Ljubobratović et al., 2021). At the time of ovulation, a sample of oocytes was taken from each female using a catheter (CH06 infant feeding tube). Immediately upon biopsy, the oocytes of each female were stocked in separate wells of 6-wells cell culture plates. Each well was filled with 90% L15 medium and 5 IU/mL of human chorionic gonadotropin. Wells were further placed onto an orbital shaker and incubated at 13°C for in total 96h. Starting from 48 h post-stimulation, IVM of oocytes were monitored each 4 h, while the same procedure in females was started 120 h post-stimulation and was p erformed each 24 h. On this way, FOM dynamics and both in vivo and in vitro latency times were assessed and correlated.
All injected females ovulated, while all the IVM oocytes samples reached germinal vesicle breakdown (GVBD). The LT in females ranged from 6 to 9 days, while in vitro oocytes took 56 to 76 h to GVBD. The strongest correlation between the LT and IVM was found in 52 and 56 h post-stimulation, showing higher correlation compared to the in vitro LT.
The IVM techniques appear to be a promising tool for estimation of optimal female state for hormonal induction as well as the prediction of the latency time in out-of-season pikeperch reproduction. Rather than using the time until GVBD during the IVM, a given FOM stage at a certain time post-stimulation might be more useful to predict the state of female readiness for ovulation induction as well as the prediction of its LT.
This research was funded by the National Research, Development and Innovation Fund of Hungary (grants PD-139053 and K138425).
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