Protection against carp erythrodermatitis following bath or subcutaneous exposure to sublethal numbers of virulent Aeromonas salmonicida subsp. nova

. A bath challenge system was used to infect carp. Cyprinus carpio L., with Aeromonas salmonicida subsp. nova, the causative agent of carp cruthrodermatitis. Bath‐challenged fish became infected with the bacterium exihibitinng typical signs of the disease, Carp that were sublethally bath exposed became infected and exhibited some skin lesions, but after one week, these quickly healed and the animals fully recovered from the infection, Naive fish that had not been previously exposed to the bacterium had mortalities of 100% when infected by the subcutaneous route and 40–60% by the bath route of infection. Carp that received sublethal infections were able to withstand subsequent lethal infection and recover regardless of the route of infection. Sublethally bath‐exposed carp were protected from subsequently lethal challenges of A. salmonicida subsp. nova for at least 5 months.