Fungal Diseases of Marine and Estuarine Fishes

Fungi are generally considered to be opportunistic, relatively weak pathogens that are problematic only when hosts are exposed to some stressful conditions or otherwise have reduced defenses. Ichthyophonus hoferi is a fungus-like agent of uncertain taxonomy that causes a systemic infection in many marine fish. Pathology depends upon the host, dosage of pathogen, and possibly strain/species of fungus. Gross clinical signs include behavioral changes, abnormal pigmentation, abdominal distension, muscle atrophy, spinal curvature, roughening of skin, and skin ulcers. In the early stages of infection, there is usually a pronounced mononuclear infiltrate in reponse to the presence of spores. Ichthyophonus is clinically very similar to other chronic inflammatory diseases, such as mycobacteriosis. Experimental transmission is easily accomplished by feeding spores or infected fish. Ichthyophonus is the only fungal pathogen that has caused significant epidemics in purely marine feral fish populations.