Morphological characterization of the Hypanus guttatus (Bloch and Schneider 1801) female reproductive tract in the Amazonian estuarine gradient during the non-gestational stage

Stingrays exhibit a wide diversity of reproductive strategies and modes of embryonic nutrition, yet comprehensive morphological descriptions of the female reproductive system remain scarce for many marine species. The present study characterizes in detail the macroscopic and microscopic morphology of the female reproductive tract of the marine stingray Hypanus guttatus , collected from an Amazonian estuary in northern Brazil. Four sexually mature non-gestational females (disc width 70.125 ± 3.79 cm, disc length 187 ± 5.77 cm) were subjected to anatomical dissection and histological analysis. The reproductive system exhibited marked functional asymmetry, characterized by complete development of the left antimere (ovary, oviduct, oviducal gland, uterus, and urogenital sinus) and severe regression of the right antimere, which retained only vestigial structures associated with the epigonal organ. The functional left ovary displayed an organizational pattern typical of matrotrophic viviparous elasmobranchs, containing follicles at various developmental stages indicative of asynchronous oogenesis. The genital duct exhibited histologically well-differentiated regions, including a specialized oviducal gland, a uterus lined with trophonemata, and a urogenital sinus. This structural pattern aligns with the reproductive anatomy described for marine Myliobatiformes, in contrast to the bilateral functionality reported for several freshwater stingray species. This study provides the first integrated morphological characterization of both antimeres in Hypanus guttatus , expanding current knowledge on the reproductive biology of Neotropical estuarine batoids and establishing an anatomical baseline for future ecological, physiological, and conservation research.