DIETARY VITAMIN-C, IMMUNITY AND DISEASE RESISTANCE IN ATLANTIC SALMON(SALMO-SALAR)

Presmolt Atlantic salmon were fed a fish meal based experimental diet supplemented with graded levels of ascorbate-2-monophosphate (AP), equ ivalent to 40, 400, 2000 and 4000 mg ascorbic acid (AA)/kg for 6 month s prior to a bacterial challenge experiment. The liver AA concentratio n reflected the dietary intake of AP, but not linearly. Growth, hemato logy and acid phosphatase activity in zymosan stimulated macrophages w ere not affected by dietary AP. Serum hemolytic complement activity wa s higher in fish fed the highest AP level, but the variation was not s ignificant. Production of specific antibodies was significantly higher in fish fed the highest AP level 11 and 17 weeks after vaccination. B acterial challenge with Aeromonas salmonicida showed increased surviva l in the 4000 AP group. Lysozyme activity in headkidney and serum comp lement activity and serum iron in fish surviving the challenge were hi gher in the 4000 AP group, indicating important roles of vitamin C on lysozyme, complement and iron in non-specific disease resistance. The results indicate that high dietary levels of AP favourably affect heal th in Atlantic salmon. Disease resistance was, however, not correlated with the AA status in the liver.