The Morphological and Genetic Diversity of the Caspian Anadromous Shad, Alosa Kessleri Kessleri (Alosidae) From the Akhtuba River (Lower Volga Region) in the Current Time Period. To the Question of the Intraspecies Structure

The paper presents data on variability of morphological and population-genetic features of the Caspian anadromous shad from the Akhtuba River for three years in a row (2020-2022). Studies of the ichthyoplankton samples for the first time reveal that the spawning of the Caspian anadromous shad occurs in the middle reach of the Akhtuba River, at a distance of 180-290 km from the upper boundary of the Volga Delta. The studied species is characterized by stable values of body length and weight, sex ratio, and morphological features in the samples. A low level of its genetic variability has been established by nuclear markers of microsatellite loci and the gene. Nine haplotypes have been identified in the gene, two of which differ significantly from the others. In general, the Caspian anadromous shad is characterized by high haplotype diversity in combination with low values of nucleotide diversity. The obtained results are descriptive and can be regarded as the initial stage (hypothesis development and discussion) of studying the structure of the Caspian anadromous shad in the Lower Volga Basin.