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RP2E INRA Université de Lorraine

Predicting the egg quality based on the oocyte diameter and in vitro maturation in domesticated pikeperch Sander Lucioperca.

8th international workshop on the biology of fish gametes. Gametes workshop., 20-23 septembre, Gdansk, Pologne

Ljubobratovic, U., Kitanovic, N., Milla, S., Marinovic, Z., Fazekas, G., Stanivuk, J., Zarski, D., Horvath, A.

2022

Unlike in wild fish, final oocyte maturation (FOM) indicators were not suitable for captive pikeperch grown on artificial diets. Therefore, our work aimed at monitoring the oocyte diameter over the last several months of the pikeperch reproductive cycle and using the techniques of in vitro biological tests of FOM (IVM). In the first year, we evaluated the minimal oocyte diameter of responsiveness to hormonal stimulation in indoor-reared females. Further on, we evaluated the oocyte diameter in preseason reproduction at the early stage of oocyte maturation competence (OMC). The third trial was devoted to monitor the oocyte diameter from the stage of late vitellogenesis until the start of the natural reproductive season. Finally, IVM techniques were used to evaluate its relationship with in vivo FOM dynamics. The first trial led to the conclusion that overgrowing 900 µm oocyte reaches the initial OMC state when fish become responsive to salmon gonadotropin releasing hormone analog stimulation. In the second trial, this minimal oocyte diameter border was confirmed and it was also shown that in preseason oocyte size directly correlates with egg quality. The outcome of the third trial showed inter-individual maturational differences in fish among common broodstock. Variability in dynamics of oocyte maturation was visible already in autumn. Likewise, this trial showed that the seasonal state of higher OMC in faster-growing oocytes leads to improper FOM visible in oil globule fragmentation and malformation of the newly hatched larvae. Finally, the potential of IVM as the evaluator of the OMC was shown in the preseason as correlation was found with the oocyte diameter and in vivo latency time (period from hormonal stimulation to ovulation). Overall our research showed individuality in domesticated broodstock visible already in vitellogenesis leading to earlier OMC compared to wild fish. Likewise, faster maturing fish appear to be sensitive to external hormones in case of more advanced OMC state. Therefore, our future research will aim at developing IVM protocols for evaluation of the optimal OMC state for artificial reproduction.

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