Abstract

The Southern ray, Dasyatis americana, and the cownose ray, Rhinoptera bonasus, are commonly displayed in public aquaria. Although quite hardy, they are subject to reproductive maladies such as dystocia, egg retention problems, and metritis. These conditions can best be prevented or managed with surgical intervention followed by appropriate medical treatment.

In an effort to prevent these reproductive disorders in a single sex collection of Southern rays, ovariectomy of the juvenile female rays is an excellent strategy. Juveniles in the 50 to 70 cm disc width make the best candidates. The rays are anesthetized and maintained with MS-222 at 75 ppm in a recirculating system. The left para-lumbar 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 3-0 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 minimal post-surgical problems and no evidence of deleterious long-term effects. There has been no evidence of the vestigial right ovary becoming active. Acquiring patients of the appropriate size and reproductive status are the only surgical limitations.

The same approach may be employed for a variety of diagnostic and therapeutic laparotomies. The para-lumbar approach has proven useful in performing c-sections on cownose ray dystocia cases. Dystocias in cownose rays are relatively common and may be due to an oversized pup or one that is presented for a head-first delivery. If the dam is well past her due date as calculated through monthly ultrasonographic monitoring, or the dam has a prolonged labor and the pup appears dead when examined with the ultrasound, a c-section is indicated. A para-lumbar is used, but the incision is made more caudally. Care should be taken not to incise into the kidney. The uterus is very vascular, but hemorrhage is easily controlled and the wall is closed with a simple continuous PDS suture. The skin is closed with PDS, and sutures are removed at one month.

Acknowledgements

The author would like to thank the aquarists at the Ripley's Aquariums.