Morphology and fine structure of the Russian sturgeon, Acipenser gueldenstaedtii (Acipenseridae, Chondrostei) spermatozoa

Spermatozoa morphology and fine structure were studied in the Russian sturgeon, Acipenser gueldenstaedtii (Acipenseridae, Chondrostei) spermatozoon using scanning and transmission electron microscopy. The spermatozoon is composed of an elongated head (length: 6.84 ± 0.04 μm) with an acrosome (1.18 ± 0.01 μm length and 1.05 ± 0.01 μm width), a cylindrical midpiece (length: 1.64 ± 0.03 μm) and a flagellum (length: 49.42 ± 0.37 μm). Eleven to 12 postero-lateral projections (length: 0.65 ± 0.02 μm) were observed at the posterior edge of the acrosome. Three endonuclear canals was observed from the acrosome to the implantation fossa. In the midpiece, 4–6 mitochondria were observed as well as (i) a proximal centriole close to the implantation fossa and (ii) a distal centriole at the base of the axoneme. The flagellum consisted of nine peripheral microtubules and a central pair surrounded by the plasma membrane, which was extended while developing a pair of lateral fins along it. Inter-individual differences in morphological dimensions of spermatozoa were detected. Principal component analysis performed on morphological parameters revealed 74.08% of the variance for the first three components. The acrosome width, midpiece length and posterior width of midpiece were correlated with component 1, flagellar length and total length with component 2, and head length, anterior width of head, posterior width of head and anterior width of midpiece with component 3. Inter-species comparisons in Acipenseridae showed differences in morphological dimensions of spermatozoa. In this context, acrosome, head and midpiece dimensions in the Russian sturgeon were similar to those of Shortnose sturgeon, white sturgeon and Persian sturgeon. Length of the flagellum and total length of spermatozoon in the Russian sturgeon showed similarity to those of Lake sturgeon and Persian sturgeon.