Abstract
Two wild-caught pacific bonito (Sarda chiliensis) from Monterey Bay Aquarium died during quarantine without any prior clinical signs. Gross necropsy findings included skin ulceration, enlarged spleen, swollen kidney with black nodules approximately 2–4 mm in diameter, and granulomas in spleen. Black fungal hyphae were identified in renal impression smears using light microscopy. Tissue samples were submitted for histopathologic examination to the University of California, Davis. The results of histopathologic examination revealed black septate fungus in the kidney and skin. Renal and skin cultures grew a fungal pathogen morphologically identified from the genus Exophiala. Two bacterial pathogens, Vibrio alginolyticus and Photobacterium damsela, were also isolated from kidney, skin, and blood cultures. Mycotic samples were sent to the Texas Fungus Testing Laboratory for speciation, where a species of Exophiala was confirmed, and its DNA sample was sequenced at CBS in the Netherlands. The sequence revealed a novel species of Exophiala, which belongs to a clade of melanized fungi containing many water-borne fungal species. Previously, Exophiala species have been cultured from marine and fresh water fish including striped jack, Atlantic salmon, sand lance, smooth dogfish, and leafy sea dragons in captive and cultured animals.1-5 In the current case, while the origin of infection is not yet established for the bonito, the previously reported cases all involve captive or cultured fish. Thus far, no wild animal cases of Exophiala infection have been reported, and nosocomial infection is suspected for these animals. Based on the current peer-reviewed literature, this is the first case of Exophiala infection reported in bonito. Exophiala are ubiquitous in soil and water, and is a significant pathogen which can cause systemic disease, resulting in significant mortality and morbidity in some fish. It has also caused severe disease in valuable aquarium fish such as leafy and weedy sea dragons.1 Exophiala infection appears to be an emerging disease and the prevention and control of such systemic mycotic disease is critical in maintaining healthy aquarium animal collections. In addition, several species of Exophiala are also zoonotic, emphasizing a continuing need to practice best husbandry and sanitation practices when working around captive fish collections and aquaculture facilities.
Acknowledgements
The authors wish to thank Dr. Ronald P. Hedrick of Fish Diagnostic Laboratory, University of California, Davis; Ms. Anita Wong of Veterinary Teaching Hospital Microbiology Laboratory, College of Veterinary Medicine, University of California.
References
1. Nyaoke A, Weber ES, Innis C, Stremme D, Dowd C, Hinckley L, Gorton T, Wickes B, Sutton D, de Hoog S, Frasca S. Disseminated phaeohyphomycosis in weedy seadragons (Phyllopteryx taeniolatus) and leafy seadragons (Phycodurus eques) caused by species of Exophiala, including a novel species. J Vet Diagn Invest 2009; 21: 69–79.
2. Otis EJ, Wolke RE, Blazer VS. Infection of Exophiala salmonis in Atlantic salmon (Salmo salar L). J Wildl Dis 1985; 21: 61–64.
3. Carmichael JW. Cerebral mycetoma of trout due to a Phialophora-like fungus. Sabouraudia 1966; 6: 120–123.
4. Munchan C, Kurata O, Wada S, Hatai K, Sano A, Kamei K, Nakaoka N. Exophiala xenobiotica infection in cultured striped jack, Pseudocaranx dentex (Bloch & Schneider), in Japan. J Fish Dis 2009; 32 (10): 893–900.
5. Gaskins JE, Cheung PJ. Exophiala pisciphila: a study of its development. Mycopathologica 1986; 93: 173–184.