A Hyphomycete Fungus,Paecilomyces lilacinus,Associated with Wasting Disease in Two Species of Tilapia from Puerto Rico

The hyphomycete Paecilamyces lilacinus was isolated from internal tissue samples of a hatchery-raised blue tilapia Tilapia aurea and three of nine feral Mozambique tilapias T. mossambica suffering from tilapia wasting disease in Puerto Rico. Gross cultural and microscopical features of this fungus closely resemble those of P. farinosis and P. marquandii, both of which have been previously isolated from fish tissues. They also resemble features of P. fumoso-roseus, a species that has been isolated from a captive tortoise. However, the species from tilapia can be distinguished from these other species of Paecilomyces by its production of a brown exudate on Czapek yeast agar (CYA), its deep brown reverse coloration on CYA and Blakeskee malt extract agar (MEA), and its longer, more slender, solitary phialides. It can be further differentiated from these species by growth at 37 degreesC, which is absent in the other three species. Externally, infected fish were emaciated and had sunken eyes and relatively large heads. They also had eroded fins and hemorrhagic, occasionally scaleless lesions up to 5 cm wide on their flanks. Internally, their gastrointestinal tracts and body cavities contained a clear, light amber fluid. Infections were also marked by the presence of numerous golden to reddish-brown granulomas, 0.3-1.3 mm wide, throughout the internal organs. Histopathology revealed that granulomas in spleen, kidney, and liver samples from the blue tilapia and from 12 of 18 Mozambique tilapias collected between 1992 and 1998 were composed of necrotic foci containing invading hyphae, hyphal fragments, conidia, and mixed cellular and caseous material. Bacteria were not observed in the lesion material. As tilapia wasting disease is an apparently common and fatal disease in the Mandri and Santa Teresa lagoons, we recommend that further studies be undertaken to determine the source and route of infection for possible control measures.