Freshwater rays are elasmobranchs restricted to South America, with the greatest diversity of species concentrated in the Amazon region. Potamotrygon leopoldi is a freshwater ray endemic to the Xingue River basin and is commercially exploited as an ornamental resource. The present study aims to provide preliminary aspects of the reproductive biology of P. leopoldi. Specimens of P. leopoldi (n = 54) were sampled by the research team in March-April 2003 and February and April 2004 (flood period) in the middle Xingu River region (PA). Some initial observations were made in the field, but all reproductive apparatus and embryos were removed, fixed (formalin 10%) and preserved (alcohol 70%) for laboratory analysis. The males analyzed (n = 29) had mean lUS and lGS of 3.67 and 0.46, respectively. Pearson's correlation index (r) between disc width and clasper length was 0.86 and, of these specimens, 86.21 % had abundant semen. The females analyzed (n = 25) had mean lHS of 3.05 and mean lGS of 1.29. Mean ovarian fecundity was 11.60 and mean uterine fecundity was 6.54. Pearson's correlation index (r) found for the relationship between disc width and number of embryos was 0.89. The presence of uterine eggs (n = 22) and embryos (n = 130) was observed in 96% of females (n = 24). Uterine eggs and early developing embryos were observed in 62.50% (n = 15) of the pregnant females. The observation of a significant number of males with abundant semen and early developing embryos indicates that probably P. leopoldi presents part of its reproductive cycle associated with the Xingu River flood period. Possibly the processes of copulation and the beginning of gestation occur predominantly in the flood period, however, further studies are still needed to better characterize the reproductive cycle of this species.
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