Comparative study on ultrastructure and motility parameters of spermatozoa of tetraploid and hexaploid Siberian sturgeon Acipenser baerii

Siberian sturgeon Acipenser baerii is supposed to by species of functionally tetraploidy (4n). Large-scale screening of ploidy levels of various sturgeon stocks revealed one hexaploid (6n) male specimen producing triploid spermatozoa. Spermatozoa of three tetraploid individuals were compared with those of the hexaploid specimen in terms of ultrastructure and motility features. All evaluated morphometrical characteristics of the acrosome, the head, the midpiece and the flagellum showed significantly higher values in spermatozoa of 6n in comparison with 4n Siberian sturgeon males. Mean values of velocities at the beginning of activation differed highly significant between spermatozoa of 6n (155.19 and 158.22 mu m s(-1)) and 4n males (181.05 and 179.21 mu m s(-1)) in time 15 and 30 s post activation. Nevertheless their velocities did not show significant differences between spermatozoa of 6n (149.35 and 154.16 mu m s(-1)) and 4n (158.00 and 152.66 mu m s(-1)) in 30 and 45 s post activation. It was supposed that the bigger head of 6n male spermatozoa inhibited motility at the beginning of activation, but later the longer flagellum and bigger midpiece with higher number of mitochondria can partially balance the increased sizes of heads in spermatozoa movement of male with higher ploidy level.