2.6. Challenge test
The seven-day lethal dose 50 (LD50) for A. hydrophila MTCC-1739
was 107 cfu/mL as determined earlier in our laboratory [24]. At the
termination of the feeding trial, ten fish from each tank (i.e.
3 10 ¼ 30 fish per group) were picked out for challenge test. The
fish were injected i.p with 100 mL of phosphate buffer saline (PBS)
containing 1 107 live A. hydrophila. For negative control, a group
of 10 fish were injected with PBS only. The challenged fish were
kept under observation for 15 days and fed a basal diet. The mortality
of fish in each tank was observed over the course of 15 days.