TISSUE LOCALIZATION AND IMMUNE-RESPONSES IN ATLANTIC SALMON, SALMO-SALAR L, AFTER ORAL-ADMINISTRATION OF AEROMONAS-SALMONICIDA, VIBRIO-ANGUILLARUM AND VIBRIO-SALMONICIDIA ANTIGENS

The tissue localisation of formalin-killed radioactive labelled Aeromo nas salmonicida, Vibrio anguillarum and Vibrio salmonicida delivered o rally to Atlantic salmon (Salmo salar) was investigated. The bacteria were delivered by intubation directly into the stomach, and binding/up take of radiolabelled protein antigens in four gut segments (stomach, pylorus, midgut and hindgut) spleen, blood and kidney was recorded ove r a 7 day period (5, 12, 24, 72 and 168 h). The peak concentrations (c pm) of antigens in stomach, pylorus, midgut and hindgut was at its hig hest 5, 12, 24 and 48 h after intubation, respectively. Binding/uptake of antigens in the gut was generally higher in starved fish compared to fed fish. Also, the concentrations of specific antibodies in serum, gut and skin mucus after intraperitoneal, oral and anal administratio n was investigated. Generally, the antisera obtained after intraperito neal immunisation showed high antibody titres against the homologous a ntigens whereas no specific antibodies could be demonstrated in serum after oral administration. Although gut mucus contained a low antibody titre after oral administration of A. salmonicida (A-layer positive), no specific antibodies could be demonstrated in skin mucus up to 10 w eeks after intraperitoneal, oral or anal administration of this antige n.