Meeting Abstract
Freshwater stingrays possess a unique combination of the ovaries (OV) and epigonal organs (EPO) into a single ovary-epigonal mass (OEM) that demonstrates both morphological and physiological lateral asymmetry. We examined OEM and uteri (UT) of six species of potamotrygonids in order to quantify the volume of OV and EPO within the OEM, to describe OV histology and UT morphology during different reproductive stages, and to verify a possible correspondence of lateral asymmetry between OEM and UT. OEM and UT of all species were examined both macroscopically and microscopically. Stereological techniques were used to quantify volume in an unnamed Potamotrygon species (“cururu stingray”). All of the species examined demonstrated lateral OEM asymmetry. The left OEM of Potamotrygon sp. was ~55 times larger and contained more macroscopically visual ovarian follicles (averaging 4 per left OV vs. usually absent in the right). The right OEM was composed of 7.3% OV tissue and 92.7% EPO tissue by volume, whereas the left side was 51.2% OV and 48.8% EPO. Seven phases of follicular development were identified in the OV with different compositions of follicular stages in each side. UT were symmetrical and the fecundity ratio between the right and left sides was 0.9:1.1 (right:left). Despite the volumetric difference in OV between the two sides, UT fecundity suggests that both OV are functionally symmetric and that ovarian fecundity alone is not an accurate measure of reproductive potential.
