Enhanced immune response and protection rainbow trout to Aeromonas salmonicida bacterin following prior immersion immunostimulants

Bathing rainbow trout for 30 min in immunostimulant solutions before a 2 min bath in Aeromonas salmonicida O antigen bacterin elevated both the nonspecific defence mechanisms and the specific immune response. Levamisole, a known T lymphocyte stimulator in mammals; QAC, a quaternary ammonium compound, and ISK a short-chain polypeptide, heightened the neutrophil oxidative activity as measured by nitroblue tetrazolium assay and increased the phagocytic uptake of glutaraldehyde-fixed sheep red blood cells. The heightened activity of the specific immune response was monitored by counting numbers of plaque-forming cells, and by demonstrating elevated circulatory antibody titres. Protection levels against the virulent pathogen were also increased when the fish were challenged 14 days later. Giving an immunostimulatory bath before the antigen bath is a relatively easy method of increasing efficacy and potency of immunogens for the prevention of diseases in fishes.