Abstract
The Southern stingray, Dasyatis americana, are large rays that are commonly displayed in public aquariums. In aquariums, as well as in the wild, female Southern rays are reproductively active and can produce 2 to 10 pups a year. Female Southern rays are seldom not gravid1 as they are impregnated within days of parturition. The uterus never undergoes involution and the ray's ovary is constantly producing follicles for the next litter of pups. To decrease the overproduction of rays in captivity, many aquaria have resorted to single sex exhibits that are inhabited by large female rays. When there are no males to impregnate the female her uterus continues to act as if she is gravid, and produces a large amount of histotroph2 to feed pups that are not present. This accumulation of histotroph leads to an extreme mucometra. Follicle production without ovulation and fertilization also causes the ovary to become cystic and achieve enormous proportions. While the mucometra may be treated by cannulating the cervix and evacuating the uterus, this condition recurs in a few months due to the abnormal ovary.
In an effort to prevent these reproductive disorders in a single sex collection; ovariectomy of some of our juvenile female rays is being pursued. The rays are anesthetized and maintained with MS-222 at 75 ppm in a recirculating system. The left paralumbar area is sanitized with an iodine solution. An incision is made parallel to the spinal column and 2 cm lateral to the dorsal lumbar muscles. After incising the peritoneum the cranial portion of the ovary and the enveloping oviduct are dissected free, clamped and ligated with a single encircling ligature. This pedicle supplies the majority of the blood supply to the ovary. The suspensory ligament from the ovary that runs along the mid line is transected and mosquito forceps are applied for hemostasis as necessary. The caudal pole of the ovary is broadly attached to the cranial end of the epigonal gland. This is bluntly separated with very little hemorrhage. The peritoneum and skin are each sutured with 3-O PDS in a simple interrupted pattern. Sutures are removed one month after surgery. The rays recover rapidly and feed within hours of the surgery.
To date there have been no post-surgical complications but it is too early to tell if removal of the ovary in sub-adult animals will cause any subsequent growth, metabolic, or reproductive problems in the future. A surgical limitation is acquiring patients of the appropriate size and reproductive status.
Acknowledgements
The author would like to thank the aquarists at the Ripley's aquariums for their professional support in handling the large numbers of animals involved in this project.
* Presenting author
Literature Cited
1. Henningsen A. Notes on reproduction in the Southern stingray (Dasyatis americana), Copeia, 2000(3):826–828, 2000.
2. Myleniczenko N, Penfold L. 2012. Ultrasound findings in Southern Stingrays (Dasyatis americana) with and without reproductive disease. Proceedings IAAAM, 2012.