Spontaneous occurrence of ploidy abnormalities in sterlet: is it necessary to fertilize sturgeon eggs immediately post-collection?
Sturgeons are the most endangered group of animals in the world. Artificial reproduction of sturgeons serves as an essential source of material for restocking, commercial purposes, and research. However, the recent findings suggest that hatchery practice can remarkably affect the genetical quality of sturgeon progeny. Namely, bad practice can result in an increased production of ploidy-abnormal specimens, i.e., the individuals possessing species-atypical numbers of chromosome sets in cells. Among the most common are biological triploids with three sets instead of two; another type of abnormal ploidy is mosaicism—the presence of cells with unequal numbers of chromosome sets. These specimens can exhibit impaired gametogenesis and lower fitness than their counterparts of common ploidy. This raises concerns about how to prevent the undesirable occurrence of abnormal individuals.
The present study deals with several aspects of artificial reproduction in sterlet, a sturgeon species that is native to the Czech Republic. Primarily, it focuses on the effect of storage duration of collected eggs (in vitro ageing) on the ploidy structure of the progeny and its yields. Apart from this, different concentrations of fertilization environments were tested based on the previous finding that the using of high numbers of spermatozoa per one egg contributes to the incidence of mosaicism. Last but not least, we evaluated the effect of elevated spawning temperature combined with previously mentioned factors and other aspects of artificial reproduction.
The results of the study conducted using 22 sterlet females confirmed that sturgeon eggs do not need to be fertilized immediately post-collection. When females are held at 15°C before being stripped and individual egg batches are stored in ovarian fluid at the same temperature, the eggs can be fertilized within 6 h without the risk of decreased quality or quantity of the progeny. However, this conclusion is valid only for females with normal latency—eggs of females ovulating considerably later than the majority of the spawners should be omitted from reproduction or, at least, fertilized immediately post-collection. The fertilization environment of 105 spermatozoa per egg with an egg:water ratio of 1:4 was proven to be optimal; tenfold increase in the concentration of spermatozoa resulted in an elevated incidence of mosaicism, while a considerably diluted environment did not yield significantly fewer abnormal individuals than 105. Apart from this, we confirmed the harmful effect of elevated spawning temperature on eggs—when 18°C was used instead of 15°C, the occurrence of ploidy abnormalities (mostly triploids) often reached as much as 75%, and in one of the females, even 100%.
More detailed information can be found in the original scientific article:
Hubálek, M., Flajšhans, M., Tichopád, T., Prášková, E., Michalcová, K., Kašpar, V., 2026. In vitro egg-ageing and sperm quantity in the artificial reproduction of sterlet (Acipenser ruthenus): is ‘the less, the better’ a good rule for avoiding ploidy abnormalities in small sturgeon species? Aquaculture 619: 743881.
