Optimizing the gonadoliberin dosage and evaluating the egg quality in the preseason and seasonal artificial reproduction of pond-reared sterlet Acipenser ruthenus.

Sterlet Acipenser ruthenus is the smallest in size, early maturing, yet third in production scale among the sturgeon species and as such presents a good model to study reproductive biology. The present study aimed to evaluate the effects of preseason artificial reproduction and reduction of hormonal dosage on the egg quality in pond-reared sterlet. Therefore, a series of three trials were conducted in the period 2021 and 2022 (21 and 22) that evaluated three dosages of mammalian gonadotropin releasing hormone analog des-Gly-(d-Ala)-GnRH (40, 20, and 10 µg/kg) in both preseason (January) and seasonal (April) spawning batches (PRE and SEA). The greatest embryo survival was achieved in SEA-21-10 (84.8 ± 5.8 %) and the lowest in PRE-21-40 (31.0 ± 40.7 %). Overall results indicated that a dosage of 10 µg/kg leads to the highest embryo survival. Considering the season, latency time was significantly longer in preseason reproduction being on average about 6 h prolonged (35.1 ± 2.8 h vs. 41.4 ± 2.9 h) and it directly affected the embryo survival (linear correlation r = - 0.769, P = 0.003). Likewise, preseason reproduction yields more variable egg quality, due to impaired performance of later ovulating fish most likely due to lower oocyte maturation competence. The present study found expected latency time at 14 °C to be 37-41 h in the preseason and 31-41 h in season, while the recommended dosage is 10 µg/kg des-Gly-(d-Ala)-GnRH. Future studies should develop in vitro tools to evaluate the oocyte maturational competence to improve the egg quality in the preseason.