Meristic and morphological features of the Baltic sturgeon (Acipenser sturio L.)

In order to perform a population recovery program of the common sturgeon, A cipenser sturio, of the Baltic Sea, it was necessary to define the morpholo gical, genetical and ecological characteristics of this species. Although t he sturgeon was an important commercial fish until the beginning of the 20t h century, only one study gathered a complete morphological description whi ch wa based on 5 preserved specimens (Marti, 1939). Due to the quasi extinction of the North European sturgeon population the o nly option to investigate the morphology of the Baltic sturgeon was to coll ect data from Museum specimens. 27 museal specimens and one live individual were included in the morphological analysis, using the conventional Russia n methodology as well as the method of trust network measurement. Studying the literature on classical morphometry of A. sturio, different methods for measuring head length were identified and their relevance is discussed. It is concluded that because of the variability of the sturgeon's rostrum due to mechanical damages during the life (mainly through scraping against sub strates while feeding) the morphological investigations should not use dist ances related to the tip of the snout. Comparing the amount of dorsal and l ateral bony plates, the Baltic sturgeon seems to differ from A. sturio from the Gironde (Atlantic Ocean) and the Rioni (Black Sea). The meristic diffe rences between A. sturio from the Baltic Sea, Atlantic Ocean and Black Sea may show a boundary effect of the narrow North Sea- Baltic Sea connection. However, the rhombic denticles between the dorsal and lateral plates and th e same radially striated structure of the dorsal plates of common sturgeon living in European waters seem to point to the existence of only one specie s in the region. Further ecological (Spawning behaviour), and genetic (karyotype and DNA-seq uencing) studies are envisaged to document whether geographical distance le ads to genetic differences among specimens originating from a larger Europe an region.