Epidemic Oral Ulceration in Largemouth Bass (Micropterus salmoides) Associated with the Leech Myzobdella lugubris

An epidemic of severe ulcerations of the tongue and buccal cavity was documented in subadult and adult largemouth bass (Micropterus salmoides) from Currituck Sound, North Carolina (USA). Other external clinical signs were not present. Between November 1986 and May 1987, reports from fishermen indicated that as many as 90% of large (>300 mm total length) bass were affected. Older fish were the most commonly involved. The leech, Myzobdella lugubris (=Illinobdella moorei), was consistently present on or near the lesions. Lesions were heavily infected with several different bacteria that were apparently secondary invaders. Stressful (high) salinity or an interruption in the normal migratory cycle of the parasite are suggested as possible causes for this condition in these bass.