Characterization of the genetic structure in aquaculture and wild sterlet (Acipenser ruthenus Linnaeus, 1758) populations based on microsatellite analysis

Sterlet (Acipenser ruthenus L. 1758) is one of the smallest and short-cycle species among fish of the Acipenseridae family, with the widest distribution area. For conservation and proper use of this species which was commercially important in the recent past but now is in a depressed state, information on genetic diversity in its populations is crucial. In this work, based on the analysis of polymorphism of 12 microsatellite loci, we assessed the genetic variability of several hatchery and natural populations of sterlet from the basins of the White, Caspian, Kara, Azov and Black seas. The research was carried out in 2023-2024. Fragments of pectoral fins ( n = 191) of aquaculture and wild individuals were used to isolate DNA. The origin of the aquaculture fish was as follows: the Oka (OK, n = 50, Mozhaisk production and experimental fish hatchery, Goretovo village, Mozhaisk Urban District, Moscow Province), Nizhnevolzhsky (NV, n = 34, ASTU aqua complex, Astrakhan, Astrakhan Province) and Sukhonovsky (SX, n = 35, RTF Diana, Kaduy river, Kaduysky District, Vologda Province). The wild fish samples represented five populations, the Kuibyshevskaya (KV, n = 16, Volga River, Republic of Tatarstan), Saratovskaya (SV, n = 16, Volga River, Saratov Province), Don (DN, n = 14, Don River, Rostov Province), Vyatskaya (VT, n = 16, Vyatka River, Republic of Tatarstan) and Yeniseiskaya (EN, n = 10 Yenisei River, Krasnoyarsk Territory). Polymorphism of 12 STR microsatellites, the Aru13, Spl-163, An20, LS-68, AoxD161, AfuG 41, Afu 68 b, AfuG 51, LS-39, AfuG 63, AfuG 112, Aru18 was determined using genetic analyzers (an ABI3130xl, Applied Biosystems, USA and NANOFOR 05, NPK Synthol, Russia). To assess genetic diversity, allelic diversity (AR) adjusted for sample size, observed (HO) heterozygosity, unbiased expected (UHE) heterozygosity and coefficient of inbreeding (UFIS) based on unbiased expected heterozygosity were calculated. To assess the origin, dispersion and relatedness, and to characterize the genetic structure and genetic relationships between the studied samples of sterlet, we used Principal Component Analysis (PCA) and calculated the values of the pairwise matrix genetic distances F ST and Jost’s D, followed by construction of dendrograms “network of neighbors” in the SplitsTree 4.14.5 program. According to the results of genetic analysis, the group of aquaculture samples from ASTU (NV) had the lowest values of HO (0.566±0.098) and UHE (0.573±0.089). In all other seven sterlet populations, HO varied from 0.569 in SX to 0.708 in EN, and the UHE values were higher than 0.6. In the seven studied sterlet groups, low positive values of the inbreeding coefficient (FIS) were noted, the confidence interval (CI 95 %) of which overlapped the zero value, indicating unreliable deviations of the number of heterozygotes from that theoretically expected in these samples. The exception was the Yenisei sterlet population with negative values of the inbreeding coefficient, indicating an excess of heterozygotes (UFIS(EN) = -0.1).The use of several statistical approaches revealed that the Yenisei population is the most isolated in genetic structure. Vice versa, similarity in the frequency of common alleles, common genetic structure and a low level of genetic differentiation were identified between groups of fish belonging to the Volga-Caspian (Oka, Upper Volga, Middle Volga and Vyatka origin) and Azov-Black Sea (Don population) basins. The data obtained in our work on the genetic diversity, genetic similarities and differences between individual hatchery herds of sterlet, as well as wild populations of the Caspian, Kara, Azov-Black Sea basins can be used to plan the broodstocks management and the conservation of the unique gene pool of the species A. ruthenus . To expand our understanding of the genetic structure of the Russian sterlet gene pool, these studies will be continued on larger samples and a wider range of samples from other aquaculture stocks and natural populations.