TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000   Laboratory Studies On Aphanomyces invadans From Atlantic Menhaden     V.S. Blazer1, W.B. Schill1 and J.H. Lilley2   1National Fish Health Research Laboratory, USGS, 1700 Leetown Road, Kearneysville, WV 25430; 2Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, UK and Aquatic Animal Health Research Institute, Bangkok, Thailand     Ulcerative lesions in Atlantic menhaden, Brevoortia tyrannus, along the eastern coast of the United States have generated a great deal of concern during the past few years because of their supposed relationship to the toxic dinoflagellate Pfiesteria. Consistently, however, in menhaden collected during fish kills or fish lesion events in the Chesapeake Bay, we have found a highly invasive fungal pathogen within these ulcers which consist of chronic, granulomatous inflammation extending deep into the muscle. In 1998, from lesioned menhaden in the Pocomoke and Wicomico Rivers, MD, we were able to isolate a slow-growing, aseptate oomycete. By morphology, temperature-growth curves, salinity-growth curves and PCR analysis these isolates are identical to Aphanomyces invadans from Thailand, Japan and Australia. They are also very different than the saprophytic Aphanomyces previously isolated from ulcerative mycosis of menhaden.  A.invadans, the cause of EUS (epizootic ulcerative syndrome, has caused significant losses of freshwater and estuarine, cultured fishes throughout the Indo-Pacific. We have reproduced lesions identical to those observed in natural outbreaks of EUS and in menhaden collected in tributaries of the Chesapeake, by intramuscular injection of zoospores of the menhaden isolate in both menhaden and snakehead. The progression of these lesions will be demonstrated. In addition, using PCR methodology we have demonstrated positive results in menhaden collected in estuarine environments in New Jersey, Delaware, Virginia, South Carolina, and Georgia. We have not yet been able to acquire any properly fixed menhaden samples from North Carolina. We have also received a positive reaction within the ulcer of a largemouth bass from a freshwater pond in Georgia. These results suggest that A. invadans may be having a significant effect on fish populations along the East Coast of the United States.     Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page