Changes in serum protein and IgM concentration duringsmolting and early post-smolt period in vaccinated and unvaccinated Atlantic salmon (Salmo salar L.).

During smolting the concentrations of serum protein and IgM were measured.A Vibrio salmonicida vaccine was given once or twice at various times to study the effect of smolting on vaccination. smolting there was a decrease of both total serum proteins and totalserum IgM of 24%. After sea water transfer, the total serum protein concentration increased to levels similar to those before smolting and remained stable at this level throughout the observation period. The total IgM concentration increased immediately after sea water transfer and 4 weeks later it was similar to levels before sea water transfer. In September, 4 months after sea water transfer, the IgM concentration was twice the concentration before smolting. and length were not affected by primary vaccination, while groups secondary vaccinated after sea water transfer were significantly smaller than those secondary vaccinated prior to sea water transfer. served decrease in total serum protein and IgM during the parr-smolt transformation and the subsequent increase of IgM after sea water transfer and in the autumn indicate a potential variation in immunocompetence, suggesting that the timing of vaccination with respect to developmental stage or smolt status has an impact on the immune response.