The reaction of the immune system of fish to vaccination: development of immunological memory in carp, Cyprinus carpio L., following direct immersion in Aeromonas hydrophila bacterin

. The development of immunological memory was investigated in carp following direct immersion in Aeromonas hydrophila bacterin. A single bath did not induce an increase in serum antibody (Ab) levels. A second bath at 1, 3 or 8 months resulted in clear secondary Ab responses. The highest Ab levels were reached in the group boosted after 3 months. However, at 12 months a second bath gave no further significant response. When a booster was given at the same intervals by intramuscular injection, instead of immersion, the induced memory was not expressed as a clear secondary response. It is concluded that direct immersion in a bacterial antigen did induce immunological memory. The duration of this slowly developing memory is limited in time (less than 12 months) and was only demonstrated following a second immersion. This last feature suggests the existence of a local or mucosal activity during the immune response after bath vaccination.