At the Research Center for Fisheries and Aquaculture MATE AKI HAKI in Szarvas, Hungary protocols were refined for early hormonal stimulation of ovulation in pikeperch. In this region, the typical spawning period for wild pikeperch is April. For decades, pond-reared pikeperch have been successfully spawned upon injection in January. This study aims to produce high-quality gametes an additional month earlier, in December, thus “exceptionally early.” Methodologies were developed to evaluate the oocyte maturation competence (OMC) in females based on the size of their oocytes and in vitro maturation dynamics. We evaluate exceptionally early-term ovulation stimulation in breeders grown in-pond conditions. Fish are transported from Fodina Fish Farm to MATE AKI HAKI in December. Fish are anesthetized and injected with 5 µg/kg of salmon gonadotropin-releasing hormone at water temperatures of 4-6 °C. At the time of injection, oocytes from each female are sampled using biopsy and photographed for size. One day after hormonal treatment, water temperature is increased by 1 °C each day until reaching 10 °C, when the final oocyte maturation (FOM) stage is evaluated. When fish oocytes reach germinal vesicle breakdown, the genital papilla of the respective female is sutured, and fish are moved to a 12 °C tank. This thermal transfer ensures ovulation in the following 24 h. Ovulation is evaluated at 9-, 15-, 20- and 24-hours post-suture. Non-synchronized ovulation is common in pikeperch but the described protocol enables high synchronization efficacy.
Fertilization takes place immediately after egg collection; egg adhesiveness removal is performed using a milk solution for 30 minutes, and finished with a kaolin solution bath. Egg volume is measured and stocked in the incubation jar. During incubation, eggs are cleaned from dead eggshells 2x per day. The volume of remaining embryos is again measured at 72 h post-fertilization to calculate the embryo survival rate, commonly used for the evaluation of the egg quality. One day after eye pigmentation, incubation water is hyperoxidized to force synchronous hatching. This study will determine the correlation between oocyte size at the time of hormone injection, latency time and embryo survival rate. Finally, feasibility of the artificial reproduction in the exceptionally early term will be discussed.