Morphology, chemical contents and physiology of chondrostean fish sperm: a comparative study between Siberian sturgeon (Acipenser baerii) and sterlet (Acipenser ruthenus)

The present study was carried out with two sturgeon species, Siberian sturgeon (Acipenser baerii) and sterlet (A. ruthenus) to compare spermatological parameters to better understand inter‐species differences. Significant differences between morphometric features were observed such as acrosome length, acrosome width, head length, midpiece width and flagellar length, while midpiece length did not reveal such differences. The sterlet has a shorter spermatozoon than the Siberian sturgeon. Ultrastructural parameters vary significantly in terms of length of the nucleus, diameter of the endonuclear canals (EC), size of posterolateral projections (PP) and diameter of flagellum. Mean values for density of spermatozoa in the semen, seminal plasma pH, osmolality (mOsmol kg^?1), along with Ca²⁺, Na⁺, K⁺, Cl^? ions concentrations (mm ) were determined to be 0.61 ± 0.37 × 10⁹, 8.16 ± 0.18, 77.20 ± 52.28, 0.24 ± 0.06, 31.39 ± 10.21, 3.51 ± 1.10, 14.00 ± 4.30 in A. baerii and 0.41 ± 0.32 × 10⁹, 8.13 ± 0.19, 50.74 ± 6.27, 0.16 ± 0.11, 20.11 ± 3.78, 1.26 ± 0.54, 6.11 ± 0.60 in A. ruthenus, respectively. Significant differences were observed in Na⁺, K⁺ and Cl^? concentrations in the seminal plasma as well as in sperm velocity. The percentage of motile spermatozoa did not show any significant difference between the two species. Comparing the results of this study with published literature data on sturgeon spermatozoa reveals that morphological and ultrastructural parameters of spermatozoa together with some parameters of the seminal fluid and spermatozoa velocity can be used in comparative spermatology to better understand inter‐species differences. The observed biochemical and physiological differences should be also considered for the development of methods for controlled reproduction and for sperm cryopreservation techniques.