Introduction
Among native sturgeon species of the Danube River, specimens of sterlet (Acipenser ruthenus), ship sturgeon (Acipenser nudiventris) and Russian sturgeon (Acipenser gueldenstaedtii) have also been found in the Middle Danube Basin in the last 45 years (Harka-Sallai, 2004). Out of these species, only the sterlet has permanent self-sustaining populations. However, it is possible to assume that anadromous species, may also exist as populations that have switched to potamodromous - freshwater life cycle (Pintér, 1987). Individuals from these populations are also rare to found because these endangered species are on the edge of extinction. In the case, when a genetically valuable wild individual is caught it may be necessary to reproduce, even if only one of the sexes was caught. Reproduction of such individuals may increase the number of individuals in these closed stocks by restocking of the offspring. In the case of breeding a male when only the chromosomes of the male take place in the reproduction, the method of androgenesis is used, and in the case of a female, the method of gynogenesis. However, since many thousands of individuals can be reintroduced after a successful breeding, it is necessary to develop a method that will contribute to the safe restocking of individuals with the appropriate genetic background without costly and slow genetic testing.
Materials and methods
To develop uniparental propagation methods, Russian sturgeon was used as a model animal and gynogenetic propagation method was selected. Sperm from three species such as paddlefish (Polyodon spathula), Siberian sturgeon (Acipenser baeri) and Russian sturgeon were irradiated with Co60-ϒ ray and portions of eggs of a Russian sturgeon were fertilized. If there are no viable hybrids of the two species used for gynogenesis, the result of gynogenesis will certainly be 100% without any other assay (Peruzzi et al., 1993). In the Acipenseridae family, species hybridize more effectively to each other than in other fish species (Birstein et al., 1997), therefore paddlefish seemed to be an adequate choice because it is out of the Acipenseridae family and belongs “only” to the order of Acipenseriformes. The assumption was that there is no hybrid with other sturgeon species, thus hatched offspring are certainly be gynogenetic offspring. Siberian sturgeon, on the other hand, hybridize effectively to Russian sturgeon, also due to the chromosome number match. Portions of 3 x 100-gram egg from a female Russian sturgeon was fertilized with irradiated and unirradiated sperm. The eggs were incubated in a Zuger-jars in 16 ± 1.5 °C water with 98 ± 4.5% oxygen saturation. The hatched larvae were placed in 250 l tanks in a recirculation system. For the first 4 days, artemia (Artemia sp.) and then cut red chironomus larvae (Chironomus sp.) were used ad libitum for feeding.
The fertilization rate, hatching rate and the average body mass of offspring 35 days of post hatch (DPH) was determined. The success of gynogenesis treatment was genetically determined by microsatellite analysis.
Results
Our results are summarized in the first table (Table 1):
Our results show that by fertilizing the eggs of the cutting case, we obtain a viable hybrid with the eggs of the Siberian sturgeon and the Russian sturgeon. Thus, the principle of using the species with which the target species cannot hybridize because the hatched larvae are certainly gynogenetic offspring is not met. Based on the microsatellite results of 5-5-5 fish examined from the groups, it can be stated that the treated groups carried only the genetic material of the dam of the maternal species. However, it is clear that the use of irradiated Siberian sturgeon sperm is the most appropriate method for the production of gynogenetic Russian sturgeon, as the percentage of fertilization does not differ from the use of irradiated Russian sturgeon semen, while it shows better results than hatching and 35 DPH average body weight than the same species irradiated semen is used. The Siberian sturgeon has the property of hybridizing to any other sturgeon species, and its dominant phenotype determines the phenotype of the hybrid (Chebanov et al., 2018), which is thus 100% identical to the phenotype of the Siberian sturgeon. Thus, despite the fact that the Russian sturgeon and the Siberian sturgeon have a viable hybrid, due to the dominant phenotype, the hybrid individuals can be easily selected from the stock. Therefore, for the gynogenesis of a high genetic value Russian sturgeon aimed at enhance the native population, it is strongly recommended to use a Siberian sturgeon as a sperm-donor species.
References
Birstein, V.J., Hanner, R., DeSalle, R., 1997. Phylogeny of the Acipenseriformes: cytogenetic and molecular approaches. Env. Biol. Fish. 48, 127–155.
Mikhail Chebanov, Sergei Podushka, Eugeny Rachek, Dmitry Amvrosov, and Yan Merkulov: The Siberian Sturgeon (Acipenser baerii,Brandt, 1869) Volume 2, Chapter 39 – Farming 2 89 © Springer International Publishing AG, part of Springer Nature 2018 P. Williot et al. (eds.),, 290. p. https://doi.org/10.1007/978-3-319-61676-6_14
Peruzzi, S., Scott, A.G., Domaniewski, J.C.J. and Warner, G.F. (1993): Initiation of gynogenesis in Oreochromis niloticus following heterologous fertilization. Journal of Fish Biology 43, 585–591.
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