Biological indicators and traceability of the origin of Russian sturgeon juveniles in the lower reaches of the Volga River and the north- western part of the Caspian Sea

   The aim of the work: characterization of juveniles released from sturgeon hatcheries into the natural habitat with individual identification of individuals.

   Methods: Ichthyological researches in the Volga River and its watercourses were surveyed using a 4.5 m fry trawl; in the western part of the Northern Caspian, a trawl survey was carried out using a 9 m trawl and the developed grid of stations, adjusted to take into account the sea level decrease. The trophological material was processed by the quantitative-weight method, followed by the calculation of private and general indices of the filling of the digestive tracts. Molecular genetic methods for the analysis of microsatellite loci and sequencing of a fragment of the control region of mitochondrial DNA were used.

   Novelty: the origin of the Russian sturgeon and the contribution of artificial reproduction from Russian sturgeon hatcheries to the Volga- Caspian fishery basin were determined by molecular genetic methods.

   Results: The composition of food organisms and the degree of fattening of Russian sturgeon juveniles after their migration to the sea were determined. The contribution of artificial reproduction from Russian sturgeon hatcheries to the replenishment of the Russian sturgeon population of the Volga- Caspian basin in the period 2016–2021 for fingerlings was averaged 80 %.

   Practical significance: The intensity of downstream migration in the Volga River and its watercourses of juveniles released from sturgeon hatcheries was studied. The presented data was made it possible to determine the main localization sites of Russian sturgeon juveniles depending on the species composition and abundance of food organisms in the northwestern part of the Caspian Sea. Based on the results of genotyping of spawners at sturgeon hatcheries and juveniles caught in the Northern Caspian, an assessment was made of the effectiveness of the work of the sturgeon hatcheries in 2016–2021.

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