Passive transfer of specific maternal immunity does not protect Atlantic salmon (Salmo salarL.) fry against yersiniosis

In order to elucidate whether specific protective immunity can be transferred from mother to offspring in Atlantic salmon, brood fish were vaccinated repeatedly by injection against yersiniosis during the period of egg development. An increase in specific antibodies measured by ELISA againstYersinia ruckeriserovar O2, and of bacterial agglutinating titres against both serovar O1 and O2 ofY. ruckeriwas demonstrated in the serum of vaccinated brood fish. Agglutination was also detected in homogenates of freshly stripped eggs and of fry, but at equal levels in groups from vaccinated and nonvaccinated mothers. Vaccination of the brood females resulted in low levels of specific antibodies againstY. ruckeriserovar O2 in their eggs and in fry sampled one week after hatching. However, mortalities after challenge were not reduced in fry descending from vaccinated mothers. These results indicate that specific maternal antibodies are transferred from Atlantic salmon mothers to eggs and fry, but at very low levels, insufficient to protect the offspring against yersiniosis.