Lesions in the musculature of captive American plaice Hippoglossoides platessoides caused by the fungus Hormoconis resinae (Deuteromycetes)

Abstract

Round black lesions were found on the ventral slde of 8 juvenile American plaice Hippoglossoides platessoides housed in the aquarium at the Department of Fisheries and Oceans Research Laboratory, Halifax, Nova Scotia, Canada. The wild plaice caught on Sable Island Bank, Nova Scotia, were held in 800 and 3200 I tanks supplied with a continuous flow of fresh prefiltered seawater at ambient temperature. The lesions numbered 1 or 2 per fish, varied from 5 to 20 mm in diameter and usually had a large central crater. Light microscopy and SEM revealed that the ulcers were surrounded by a rim of hyperplastic epidermis and contained numerous branched, septate fungal hyphae and Gram-negative bacteria, host erythrocytes, macrophages, and cellular debris. Fungal hyphae and necrosis extended through the dermis and musculature to the vertebral column. While the epidermis was intact over smaller lesions, hyphae could be seen on the surface of the skin, and extending along the scales through the epidermis and into the dermis. The fungus was identified as Hormoconis (Cladosporium) resinae (Deuteromycetes), a species that is not only ubiquitous in terrestrial, freshwater and marine environments, but often occurs in petroleum products. This is the first record of the fungus as a pathogen in a marine organism.