Short-term holding of female broodstock at improper spawning temperature can trigger the incidence of autotriploidy in sterlet (Acipenser ruthenus)

Artificial propagation is an essential source of sturgeon progeny for both commercial and conservation purposes. However, in culture settings sturgeons often spontaneously produce offspring with altered ploidy – mainly autotriploids having in somatic cells 1.5-fold more DNA than fish of normal ploidy. The presence of autotriploids rather than individuals of normal ploidy may decrease farm productivity or wild population recovery. We tested whether or not the temperature for holding female broodstock contributes to the incidence of spontaneous autotriploidy in sterlet (Acipenser ruthenus). We compared the occurrence of autotriploidy in the progeny of females held at various temperatures ranging from the optimal range for sterlet reproduction (12, 14 and 16 °C), in the progeny of females held at optimal and two above-optimal temperatures (15, 18 and 20 °C) and in the progeny of females held at optimal and below-optimal temperature (15 and 10 °C). The respective temperatures were reached before hormonal stimulation and kept until egg collection. Eggs were stripped within 2 h post-ovulation and fertilized within 30 min; ploidy was analysed in prelarvae sampled 2–3 d post-hatching. Only low proportions of autotriploids (0–1.1%) were detected in the progeny of females held at 10, 12, 14 and 16 °C, which was the case also for females held at 15 °C. However, a considerable number of females from above-optimal temperatures (two out of three females at 20 °C and at least two out of six females at 18 °C) produced significantly higher proportions of autotriploids, with the highest proportion observed in a female held at 20 °C: 53.3%. We used water at various temperatures for the fertilization of eggs and incubation of embryos: when each of the female-holding temperatures 12, 14 and 16 °C was combined with 12, 14 and 16 °C for fertilization and incubation, the holding temperatures 15, 18 and 20 °C were combined with 15, 18 and 20 °C, and holding temperatures 10 and 15 °C were combined with 10 and 15 °C, the proportions of spontaneous autotriploids remained statistically unchanged. We performed microsatellite analysis on autotriploid progeny of some females held at above-optimal temperatures and confirmed maternal origin of the third chromosome set. Apart from autotriploids, other individuals of abnormal ploidy were detected (tetraploids, pentaploids, haplo-diploid, haplo-triploid, diplo-triploid and diplo-tetraploid mosaics), whose occurrence seemed to be low and randomly distributed. We conclude that even the short-term holding (2-day) of sterlet female broodstock at temperatures of 18 °C or higher can often result in a remarkable occurrence of spontaneously autotriploid progeny, while the holding of females at 10–16 °C and/or using of water at 10–20 °C for fertilization and incubation do not seem to affect the incidence of autotriploidy.