Establishment of route of challenge and tissue level persistence study of Aeromonas hydrophila infection in rohu, Labeo rohita for running a selection programme

Selective breeding of rohu, Labeo rohita to Aeromonas hydrophila infection requires a challenge model to obtain LD50 dose and study of bacterial persistence in survivors’ tissues. Fish were bath challenged with various routes viz., only immersion, after scale removal (with and without high stocking), after skin abrasion (with and without high stocking), under only high stocking density and after immunosuppression. Fixed dose of intramuscular and intraperitoneal injections with uniform and variable body weights and variable intraperitoneal dose g-1 body weight were attempted. Fish were challenged and tissues from internal organs were collected at different time periods. Bacterial load was detected by nested PCR-based screening using DNA extracted from various tissues. Results revealed intraperitoneal challenge g-1 body weight as the best mode to obtain LD50. Survivors could be used as brood fish for next generation breeding to get better resistant offspring since they don’t serve as carriers after 15 day post-challenge.