Abstract

Female southern stingrays (Dasyatis americana) housed in single-gender groups have presented with reproductive disorders in a number of aquaria. Two of nine adult, female southern stingrays housed in one large mixed-species aquarium, presented with decreased appetite and a prominent bulge over their caudal dorsal surfaces. Physical examination, blood collection, endoscopy, and ultrasound were performed on the animals. Ultrasound showed a severe accumulation of hypoechoic uterine and markedly enlarged ovaries with mixed-size hypo- and hyperechoic structures. Endoscopy and fluid analysis of the uterine fluid in affected animals confirmed an overabundance of histotroph. Serum analysis revealed estrogen concentrations that were markedly higher in affected females. Examination of the remaining females revealed three additional affected animals. Necropsy results in the initial females corroborated ultrasound findings and showed hemorrhagic and necrotic ovarian tissue with cystic follicles and multiple retained masses filled with yolk material that was both inspissated and fluid. Ultrasound criteria were developed to differentiate between normal and abnormal female stingrays, and hormone levels were obtained in both healthy and affected female stingrays. Initial data describes a progressive reproductive disorder, possibly linked to chronically elevated estradiol as a function of being maintained in an all-female group. The repeated production but retention of follicles appears to result in an abnormally large ovary, which together with an over exuberant production of histotroph, results in a large, fluid-filled uterus and a domed back. Further investigation into this disease process is ongoing together with the development of treatment strategies.

Acknowledgments

Special thanks to the aquarium and hospital staff at the Disney’s animal health department; Disney’s The Seas with Nemo and Friends® at Epcot®; as well as Castaway Cay®; and Daniel P. Fahy, Nova Southeastern University Oceanographic Center, Dania Beach, FL.