Materials and methods
Bacterium
A stock of A. hydrophila and Streptococcus
sp. isolates were obtained from Department
of Aquaculture, Faculty of Fisheries,
Kasetsart University. Bacterial isolates were
initially distinguished on the basis of colony
morphology and shape by growth on brain
heart infusion (BHI) agar media (Merk) for
24 hr at 30°C. The predominant types of
bacterial colonies were purified on fresh
medium. Further pathogens were identified
by examination of Gram-staining and