Extracellular Products and Endotoxin from Aeromonas hydrophila: Effects on Age-0 Channel Catfish

The effects of the extracellular products (ECP) and endotoxin from Aeromonas hydrophila grown in a defined medium were determined following intraperitoneal injection of young-of-the-year channel catfish Ictalurus punctatus. Endotoxin had no lethal effects in doses as high as 400 μg per 7.2-g fish, whereas ECP had a 48-hour median lethal concentration (LD50) of 15.7 μg per 7.2-g fish. Sublethal doses of ECP often produced many of the gross pathologies associated with A. hydrophila infections. The primary lethal factor was heat-labile at 56 C for 10 minutes, but a heat-stable component was also implicated.