Sperm motility in ocellate river stingrays: evidence for post-testicular sperm maturation and capacitation in Chondrichthyes

Abstract

Sperm maturation, as a process through which spermatozoa acquire the ability for motility activation and fertilization, is well-known for many groups of animals. This process takes place in a taxon-specific manner in different parts of male reproductive tract. In contrast to most fish with external fertilization, a large number of animals have internal fertilization where transit through the epididymis of the male reproductive tract is necessary for the completion of sperm maturation. Although Chondrichthyes are fishes, they exhibit internal fertilization and possess specific male genital anatomy that resembles mammals. The existence of sperm maturation in the epididymis of cartilaginous fishes has been proposed but has yet to be confirmed. In this study, we used mature ocellate river stingrays Potamotrygon motoro, as a representative of Chondrichthyes, collected during the natural spawning period and evaluated sperm motility parameters during transit through the male reproductive tract, and upon contact with uterine fluid. Our data demonstrate that spermatozoa acquire motility after transit through the epididymis and are stored in a motile state within a specific organ - the seminal vesicles. Moreover, these motile spermatozoa are able to increase their velocity under the influence of uterine fluid in the female reproductive tract.