THE EFFECT OF DIETARY VITAMIN-A ON THE IMMUNOCOMPETENCE OF ATLANTIC SALMON (SALMO-SALAR L)

Atlantic salmon, Salmo salar L. were maintained on diets containing lo w (0.37 mg kg-1 diet), normal (1.95 mg kg-1 diet) and high (15 mg kg-1 diet) levels of vitamin A fed at 1.5% body weight per day. After 4 mo nths, liver vitamin A levels reflected dietary intake and growth rates of all three groups were similar. Kidney leucocyte migration and seru m bactericidal activity were found to be significantly reduced in fish fed low levels of vitamin A. On the other hand, high levels of vitami n A in the diet were found to augment serum antiprotease activity rela tive to the levels found in the other dietary groups. However, phagocy te respiratory burst activity, bactericidal activity and eicosanoid pr oduction were unaffected by the dietary vitamin A regime, as were lymp hocyte functions (lymphokine and antibody production) and both serum l ysozyme and classical complement activity. That the overall immunomodu latory effect of vitamin A was small was reflected in the resistance t o Aeromonas salmonicida. No significant differences were found between the different vitamin A intake groups despite a trend to decreased re sistance in the low vitamin A diet group.