A twelve year old, male spotted eagle ray, housed at the National Aquarium in Baltimore, developed anorexia, lethargy, pallor, and weight loss over a two-week period in Dec. 2004. The ray was seen swimming in tight circles and sinking to rest on the bottom of the tank. Water quality parameters were within normal limits and no other animals were affected. A CBC revealed elevated total protein and PCV and a chemistry panel demonstrated a markedly decreased BUN. A Vibrio sp. was isolated on blood culture and was sensitive to enrofloxacin. Antimicrobial treatment was administered for 5 weeks. Despite intital improvement, the ray deteriorated rapidly and was euthanized in early Feb. 2005. A necropsy of the ray revealed severe monogenic branchitis with diffuse lamellar hyperplasia.