Follicular growth and sex steroids in adult females of the endemic Amazonian freshwater stingray Potamotrygon wallacei (Chondrichthyes, Potamotrygonidae)

This study evaluated how the plasma steroid hormones testosterone (T) and 17 beta-estradiol (E-2) are related to follicular development in regenerating females of the cururu stingray, Potamotrygon wallacei, during the rising water season of the middle Rio Negro basin. The relative weight of hepatic and ovarian tissues, as well as the morphological changes in the vitellogenic follicles, were related to the increase in the water level. Correlations between the maximum follicular diameter (MFD) and E-2 and T levels suggest a concomitant action of these steroids in controlling follicular growth. These associations support the idea that the reproduction of this species is synchronous with the local hydrological cycle of the middle Rio Negro basin.