Amoebae Associated with Ulcerative Lesions of Fish from Tidal Freshwater of the James River, Virginia

While surveying ichthyofaunal diversity in the tidal freshwater James River (near Richmond, Virginia) during March and September 1997, we observed that 40–50% of live fish collected had ulcerative lesions. Concomitant sampling upstream in nontidal reaches produced few fish with lesions (≤2%). These observations were unprecedented based on similar surveys conducted annually since 1989 and subsequently through 2000. Affected taxa included cyprinids, catostomids, ictalurids, centrarchids, and moronids, representing both resident and migratory species. During this episode of tissue ulceration, free‐living pathogenic amoebae, predominantly Acanthamoeba and Naegleria, were the primary organisms associated with lesions across all degrees of severity and across all host species. Based on the focal nature of the lesions, the lack of physical injury to surrounding tissues, the low numbers of fungi and pathogenic bacteria, the absence of Pfiesteria and related organisms, and the large numbers of free‐living pathogenic amoebae isolated from all of the lesions, we suggest the epizootic event was an instance of ulcerative amebiasis. The 1997 event in the tidal James River was the first documented case of a fish epizootic from these amoebae in North America in over 20 years and is the first such event described for a mid‐Atlantic coastal tributary.