The importance of reactive oxygen species and the antioxidant system in sperm biology has been recognized for different bony fishes but nothing is known in this regard for chondrichthyans. For the first time for cartilaginous fishes, the enzymatic antioxidant system was shown herein to be present in both fractions of sperm (spermatozoa and seminal fluid) collected from two different places (seminal vesicle and cloaca). In internally fertilizing freshwater ocellate river stingray, Potamotrygon motoro, the activity of superoxide dismutase and glutathione peroxidase was not changed upon sperm transition from the seminal vesicle to the cloaca. The activity of catalase was significantly increased for both sperm fractions at transition from the seminal vesicle to the cloaca (1.6 times for spermatozoa and 1.9 times for seminal fluid). The role of the sperm antioxidant system for different aspects of internal fertilization is discussed. The presented results are the initiatory step in uncovering the biochemical events of internal reproduction in Chondrichthyes.

Neotropical Ichthyology Laboratory Department of Biology and Zootechny Ilha Solteira School of Engineering São Paulo State University Monção Street 226 Ilha Solteira SP 15385 000 Brazil

Research Institute of Fish Culture and Hydrobiology Faculty of Fisheries and Protection of Waters University of South Bohemia in České Budějovice South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses Zátiší 728 2 389 25 Vodňany Czech Republic

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