Immunocompetence and duration of immunity againstVibrio salmonicidaandAeromonas salmonicidaafter vaccination of Atlantic salmon (Salmo salarL.) at low and high temperatures

The influence of the environmental temperature on immunocompetence and duration of immunity in Atlantic salmon was investigated. Immunity and antibody responses in fish acclimated and reared at 2 and 10° C were examined 9, 18 and 27 weeks after vaccination with aqueous and oil-emulsified vaccines. The results obtained show that both aqueous and oil-emulsified vaccines gave full protection againstVibrio salmonicidaindependent of the rearing temperature. Vaccination against furunculosis served to confirm this result. However, the antibody response was delayed or strongly suppressed by low temperature (2° C). These results show that immunity can be fully established at temperatures shown to be non-permissible for specific antibody responses in Atlantic salmon. Duration of immunity appears to be strongly correlated to temperature and vaccine formulation. Protection obtained with the aqueous vaccine was severely reduced by 18 weeks after vaccination in fish reared at 10° C. This negative effect of high rearing temperature on the duration of protection was fully prevented by the oil emulsification of the vaccine antigens. However, high temperature had no similar effect on the duration of antibody production. This may indicate that duration of antibody production and immunity is not maintained by the same mechanisms.