RETENTION OF FURUNCULOSIS VACCINE COMPONENTS IN ATLANTIC SALMON, SALMO-SALAR L, FOLLOWING DIFFERENT ROUTES OF VACCINE ADMINISTRATION

The retention of vaccine components was studied in Atlantic salmon, Sa lmo salar L., following different routes of vaccination against Aeromo nas salmonicida. Frozen tissue was collected from the spleen, head kid ney, hind gut and liver of fish that had been vaccinated by intraperit oneal injection (monovalent and trivalent vaccines), immersion and ora l administration 2,6,8 and 16 weeks previously. The trivalent injectio n group showed the highest levels of specific antibodies and was the o nly group to show protection following challenge with virulent A. salm onicida. Following intraperitoneal injection, there was an initial wid espread distribution of Aeromonas lipopolysaccharide, but by 16 weeks lipopolysaccharide was predominantly found in macrophage populations i n the spleen, head kidney and abdominal granulomas. Only small amounts of lipopolysaccharide were retained in the head kidney of the immersi on group and no lipopolysaccharide was retained in the oral group. Sma ll and inconsistent amounts of A-layer protein were present in the mel anomacrophages of the head kidney of all groups. The relative prominen ce of A-layer protein in the spleen of the trivalent injection group 8 weeks after vaccination was linked to the high levels of specific ant ibodies, and possible immune-complex trapping and the enhancement of i mmunological memory.