A. hydrophila FW52 was kindly supported by Dr. Saowanit
Tongpim. It was isolated from tilapia disease and behemolytic and
grown in brain, heart infusion agar (BHI). After incubation at 35 C
for 18 h, the cells were harvested by centrifugation at 5000 rpm for
15 min at 4 C. The 96 h LD50 was achieved from previous work[31]. At the end of the feeding trial, 20 fish from each treatment
were injected intraperitoneally with 0.1 ml of 0.09% normal saline
solution (NSS) containing a 2.24 108 cfu ml1 of A. hydrophila. The
same volume of the NSS (0.1 ml) was intraperitoneally inoculated
to each fish for the control treatment. The post survival rate was
calculated at day 15 of injection.