Thirty-two cownose rays (Rhinoptera bonasus) at the North Carolina Aquarium at Fort Fisher have become clinically affected by a fatal disease associated with a coccidian organism between 1990-96. The initial clinical signs start approximately 1-6 months after introduction into the exhibit and include distended cutaneous lymphatics and a loss of body condition. As the disease course continues, the rays slowly become emaciated while the coelomic cavity distends with fluid. Shortly before death, the epidermis becomes generally pale with a dark splotchy pattern. An erratic swimming pattern develops, slowing to a weak fluttering at the surface. Eating ceases approximately twenty-four hours prior to death.

The rays have originated from many wild sources and two aquaria which have not reported the disease in their collection. Other animals that have been in the exhibit or quarantined with the rays include sandbar and sharp nose sharks, southern, bullnose, Atlantic and blunt nose stingrays, cleamose skates, Snook, ladyfish, lookdowns, silversides, Atlantic bumpers, and horseshoe crabs. Restaurant quality quahog clams, shrimp, clams, and squid along with locally purchased whole fish are fed to the rays. All frozen items are stored at -30°C and thawed prior to feeding.

Necropsy findings include a serous to white effusion filling the coelomic cavity, generalized serositis, and cutaneous lymphangectasia. Organisms are noted in the serosal surfaces of the coelomic organs with associated lymphocytic serositis. Coccidial oocysts are readily demonstrated in the coelomic cavity but have not been found in the feces of affected rays. Coelomic and fecal samples of one Atlantic ray and one southern ray did not contain coccidian oocysts. Oocysts were not found in the sediment, foam fractionater byproducts, or filter samples.

Because the oocyst contains four sporocysts, we place the organism in the genus Eimeria. Microgametocytes and oocysts in various stages of development have been found in coelomic aspirates of live rays. Further taxonomic study is underway. Current recommendations include quarantine, entrance and exit examinations and diagnostic evaluation (including a coelomic aspirate/ coelmic wash and aspirate). Evaluation of therapeutic approaches is in progress.