Reproductive Aspects of Freshwater Stingrays (Chondrichthyes: Patamotrygonidae) in the Brazilian Amazon Basin

Abstract

Freshwater stingrays (Potamotrygonidae) are the only elasmobranchs completely adapted for living in freshwater and all species studied so far presented a reproductive mode described as matrotrophic viviparity with development of trophonemata. Several specimens were collected, dissected and had their reproductive parameters studied. The following species are being studied: Potamotrygon motoro, P. orbignyi, P. schroederi, P. scobina, Potamotrygon sp., Paratrygon aiereba and Plesiotrygon iwamae. The reproductive cycle in the potamotrygonid species observed is directly related to the hydrologic cycle. All species studied have defined reproductive periods with the following sequence of events: gonadal maturation, copulation, pregnancy, birth and resting. Each species analyzed presented a different reproductive periodicity. Gonadal maturation lasts for an average of about 3 months. Copulation does not happen during the same period of the year for all species and it takes place during the rainy or dry season. The lowest average uterine fecundity observed corresponded to 1 and the highest average value was 8. The gestation period varied and lasted between 3 to 9 months. Birth season also presented variation and may last from 3 to 4 months. A resting interval was observed in the reproductive cycle of most species. It is expected that the observation of reproductive aspects of freshwater stingrays contributes to the understanding of population dynamics of these species.