Abstract
An adult brown rockfish (Sebastes auriculatus) presented to the California Academy of Sciences Animal Health Department in May 2017 for evaluation of poor body condition and a monogenean infection. This animal was wild-caught in 2008, and had no previous medical history. Visual exam revealed that the fish spent an excessive amount of time resting on the bottom of the tank, and had a poor body condition of 3/9. On anesthetized physical exam, several bends in the ventral pelvic and pectoral fin rays were discovered along with associated proliferative skin lesions. The fin lesions were suspected to be caused by excessive bottom sitting. Skin scrape revealed 1+ monogenean infection, while gill biopsy was negative for parasites. Complete blood count revealed a left shift with 4% band cells, but normal overall leukocyte count. Plasma chemistry was unremarkable. Whole body radiographs showed a discrete area of increased soft tissue opacity present in the caudal portion of the swim bladder. Coelomic ultrasound was unremarkable. Top differentials at this time were infectious aerocystitis or a neoplastic mass. The patient was started on injectable ceftazidime and a fresh water bath was performed due to the monogenean infection.
Over the next subsequent weeks, attempts were made to collect a diagnostic aspirate sample from the swim bladder using ultrasound and coelioscopy guidance; however, attempts were unsuccessful. Five weeks after presentation, the decision was made to euthanize the patient due to progression of disease despite empirical antibiotic therapy, and due to perceived poor prognosis based on the severity of disease appreciated during coelioscopic exam.
Gross necropsy revealed an extremely thickened swim bladder wall with a 2x2.5 cm brown, caseous masses present within the caudal lumen of the swim bladder. Several small nodules were also noted on the surface of the spleen and liver and within the mesentery. The epicardium was covered in a diffuse tan adherent material. A sterile swab of the swim bladder mass was collected and submitted for microbiological analysis. Histopathology of the swim bladder revealed severe multifocal to coalescing granulomatous cellulitis and granulomas. Small hyphal structures could be identified in some of the granulomas. These were irregular hyphae with internal septation and ballooning hypha walls. In some areas, these structures were also supporting multiple round to oval deeply basophilic-staining clusters. Multiple metazoan parasite granulomas were also appreciated in the omentum, intestines, spleen, heart, hematopoietic kidney and interstitium of the gills. Culture from the swim bladder resulted in growth of a yeast in tryptic soy agar supplemented with 5% sheep blood approximately 5 days post-inoculation. Amplification and sequence of the internal transcribed spacer region identified Filobasidium uniguttulatum as the closest match in the National Center for Biotechnology Information with 96% identity.
Fungal infection of the swim bladder is a relatively uncommon diagnosis in teleost patients although several cases of fungal aerocystitis have been reported.1-5 Filobasidium uniguttulatum is a saprophytic fungus and the teleomorph form of Cryptococcus uniguttulatum. To the authors’ knowledge, this is the first report of a Filobasidium or cryptococcal infection in a teleost.
Acknowledgements
The authors would like to thank the Animal Health and Husbandry staff of the California Academy of Sciences and Dr. Kathryn Phillips of the University of California Davis for providing her radiology expertise in this case.
* Presenting author
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