Abstract

Yellow spotted stingrays (Urolophus jamaicensis) or yellow stingrays are popular display aquarium elasmobranchs which are viviparous. Their gestation period is not well documented but other species of the same genus have terms between 3 and 4 months (T. Tricas, Florida Institute of Technology, personal communication). Yellow spotted stingrays commonly conceive in captivity, but some fail to deliver offspring. The underlying etiology is uncertain, but improper environmental cues such as water temperature and salinity changes, photoperiod, nutrition, social structure, bottom substrate, or any combination of the above could contribute to the inability for gravid rays to deliver. Manually induced parturition is a viable option to resolve yellow spotted stingray dystocias.

Cases

Two adult, pregnant, yellow spotted stingrays were approximately 2 months past their expected parturition dates. Rays were kept in artificial sea water (Forty Fathoms Crystal Sea^®, Marine Enterprises International, Inc., Baltimore, MD, USA) with a crushed coral substrate. Salinity (31±1 ppt), temperature (23±1°C), and pH 8.3±1 was stable; and ammonia, nitrite, and nitrate were within acceptable parameters. The rays were fed a mixture of squid, shrimp, clams, and gel food at approximately 1–3% of their body weight daily. The rays were housed with clearnose skates (Raja eglanteria), cownose rays (Rhinoptera bonasus), Atlantic stingrays (Dasyatis sabina), southern stingrays (Dasyatis americana), bluntnose stingrays (Dasyatis sayi), and bonnethead sharks (Sphyrna tiburo).

Visual examination and palpation of the distended coelomic wall indicated an undetermined number of viable pup(s) which were observed swimming inside the uterus with a characteristic undulating motion of their pectoral fins. Both rays were induced through digital manipulation.

Throughout the dystocia, the females continued to eat and behave normally. Females were anesthetized with 300–400 ppm tricaine methanesulfonate (Finquel^®, Argent Chemical Labs, Redmond, WA, USA) and the cloaca canulated with a beveled 6-ml syringe case to examine the functional “cervix.” A Kelly forceps were introduced into the cervix, which was dilated by rotating the instrument in a slowly expanding circular motion. Clear uterine fluid evacuated once the cervix was expanded, and a gloved finger was introduced to continue dilating the cervix. The lumen was gently expanded to approximately 2 cm where two fingers could be placed into the uterus to locate one of the pups’ tails. Remember: most ray pups resemble miniature adults and have venomous barbs which could cause the surgeon serious injury and pain. Once the tail was pulled through the cervix, gentle but steady pressure was placed on the coelomic cavity to expel the fetuses from the uterus. Pups that could not be extracted in this manner were carefully removed by gentle traction on the barb using padded hemostats, thus, pulling the fetus out by its tail.

Six pups were delivered alive, four from one ray and two from the other. Ray pups started respiring 30–130 seconds after delivery. It is uncertain whether this was a physiologic response or a result of the tricaine anesthesia. Four months after manual induction the adult females were once again gravid.

Pharmacologic methods to induce parturition are currently being investigated as well as natural history data, such as gestational times and parturition cues to determine when intervention is necessary.

Acknowledgments

We thank the staff of the North Carolina Aquarium at Fort Fisher, New Hanover County, NC, USA.