Nocardiosis in sea bass, Lateolabrax japonicus, in Taiwan

An epizootic in pond cultured seabass, Lateolabrax japonicus, was caused by Nocardia sp. in Taiwan, in September and October 1997. The cumulative mort ality within 1 month was 17.5% (3500 out Of 20000 fish) and diseased fish w ere 7 months old with total lengths from 25 to 30 cm. Multiple, yellowish w hite nodules, 0.1-0.2 cm in diameter, were scattered in the gill, heart, li ver, spleen and kidney. Histopathologically, typical granulomatous lesions appeared in those organs. The morphology of isolated bacteria from brain he art infusion (BHI) medium or Lowenstein-Jensen medium (LSM) were bead-like filaments, as shown by Ziehl-Neelsen's (ZN) staining method. The gross lesi on and histopathological changes found in experimentally infected fish were similar to those in naturally infected fish. Based on the growth character istics, morphological and biochemical properties of the bacterium, and hist opathological changes, the isolated bacteria were identified as Nocardia se riolae. This is the first report of N. seriolae-infected sea bass in aquacu lture.