PROTECTION OF ATLANTIC SALMON (SALMO-SALAR L) AGAINST AN EXPERIMENTAL-INFECTION OF AEROMONAS-SALMONICIDA SSP ACHROMOGENES

To assess the protective role of cell-associated and extracellular ant igens of Aeromonas salmonicida ssp. achromogenes, Atlantic salmon were immunised either with detoxified extracellular products (d-ECP), form alin killed cells (f-Cells) or a mixture of both. In an experimental c hallenge ECPs were found to elicit better protection than whole bacter ia. The protection strongly correlated with the detection of antibodie s directed against a toxic metallo-caseinase, AsaP1, in fish sera. Pas sive immunisation of Atlantic salmon with rainbow trout or rabbit anti -AsaP1 antisera conferred significant protection against challenge wit h a virulent A. salmonicida ssp. achromogenes strain. In an equivalent experiment neither rainbow trout nor rabbit antisera containing antib odies to the A-layer protein of A. salmonicida were found to be protec tive for passively immunised Atlantic salmon. The results demonstrate the importance of humoral antibodies and neutralisation of bacterial t oxins in protecting Atlantic salmon against A. salmonicida ssp. achrom ogenes. (C) 1997 Academic Press Limited.