The sterlet (Acipenser ruthenus) is an object of restocking, valuable aquaculture species and experimental model. However, its artificial reproduction often results in the unintentional production of individuals with species-atypical ploidy and impaired physiological/reproductive performance: autotriploids and haplo-diploid mosaics. We evaluated the effects of in vitro egg ageing and the fertilization environment on the incidence of ploidy abnormalities in sterlet to propose protocol that can ensure a good balance between ploidy structure and progeny yields. We conducted two experiments involving eggs from nine females fertilized by two males. The eggs were collected within 2.5h post-ovulation and stored in ovarian fluid at 15°C (150-g portions); ploidy was analysed 2–3d post-hatching. In Experiment 1, eggs were fertilized within 20 min post-collection (0h) and after 8h using spermatozoa:egg ratios of 10⁵ and 10⁶ and an egg:water ratio of 1:4 (=4 variants). In experiment 2, two fertilization environments, 10⁵/1:4 and 10⁴/1:15, were applied to eggs stored for 0h, 3h, 6h and 12h (=10 variants). In vitro egg ageing for 8/12h affected the incidence of ploidy abnormalities (autotriploids and haplo-diploid mosaics) in 33% of females (6/18) and in some cases reduced progeny yields. Egg ageing up to 6h had a negligible effect on ploidy abnormalities, hatching and malformations in all but two females that had considerably prolonged latency. Increasing spermatozoa:egg ratio from 10⁵ to 10⁶ did not impact fertilization rate but it reduced hatching and elevated occurrence of haplo-diploid mosaicism in 44% of females (4/9). A spermatozoa:egg ratio of 10⁴ was insufficient for adequate fertilization and never produced significantly fewer abnormal individuals than 10⁵. We conclude that storing regularly collected sterlet eggs up to 6h at 15°C and fertilization using 10⁵ spermatozoa:egg and 1:4 egg:water ratio will ensure low incidence of ploidy abnormalities and high progeny yields, and that late-ovulating females should be used with caution.       
 

Artificial reproduction,ploidy abnormalities,second polar body retention,polyspermy,spermatoza:egg ratio