CHANGES IN SERUM-PROTEIN AND IGM CONCENTRATION DURING SMOLTING AND EARLY POST-SMOLT PERIOD IN VACCINATED AND UNVACCINATED ATLANTIC SALMON (SALMO-SALAR L)

During smelting the concentrations of serum protein and IgM were measu red. A Vibrio salmonicida vaccine was given once or twice at various t imes to study the effect of smelting on vaccination. During smelting t here was a decrease of both total serum proteins and total serum IgM o f 24%. After sea water transfer, the total serum protein concentration increased to levels similar to those before smelting and remained sta ble at this level throughout the observation period. The total IgM con centration 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 t he concentration before smelting. Weight and length were not affected by primary vaccination, while groups secondary vaccinated after sea wa ter transfer were significantly smaller than those secondary vaccinate d prior to sea water transfer. The observed decrease in total serum pr otein and IgM during the parr-smelt 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 smelt status has a n impact on the immune response.