TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000     Brain Parasite In Cultured Yellow Perch     Helen Acland1, Hamish Rodger2 and Fred Rommel1 1Pennsylvania Veterinary Laboratory, Department of Agriculture, 2305 N. Cameron St., Harrisburg, PA 17710 USA; 2University of Pennsylvania School of Veterinary Medicine, 3800 Spruce Street, Philadelphia, PA 19104 USA                 An as yet unidentified parasite resembling a myxosporean has been found by microscopic examination of sections of brains of Yellow Perch (Perca flavescens) being raised in culture at 19oC in a freshwater recirculating system of 140,000 gallons.  Although there were low numbers of opportunistic bacteria isolated from internal organs of some fish, there was neither definitive evidence of a virus in any tissues examined nor were other parasites seen. Water quality parameters monitored by the facility were normal. Mortality was 99% in more than 100,000 fish obtained in 1998 and 1999. Fry of 1-3 g and unknown age were purchased from a hatchery in a different state and it was reported that wild fish were used as stock to breed and obtain young fish. From the outset, the small fish introduced into the recirculating system exhibited clinical signs of hyper-excitability and later lethargy.  Abnormal swimming behavior was observed as mortality began to increase three to five months after introduction into the system.   Yellow Perch fry obtained from a different source and placed in the recirculating system reported here have shown no clinical signs or histological evidence of the parasite after six months. Other Yellow Perch from the same source reported here, but presumably hatched at a different time and sold to another producer with a recirculating system in an adjacent state, have not shown any evidence of the brain parasite.  The lesions in the brain are multiple meningeal and ependymal nodules composed of enormous numbers of spores, which infiltrated the optic lobes and cerebellum of the brains of some fish with minimal  inflammatory response. Preliminary DNA analysis of the parasite confirms that it is not  Myxobolus. cerebralis, M. arcticus nor M. neurobius and is the subject of further investigation.     Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page