INTERACTION BETWEEN 2 DIETARY LEVELS OF IRON AND 2 FORMS OF ASCORBIC-ACID AND THE EFFECT ON GROWTH, ANTIOXIDANT STATUS AND SOME NONSPECIFICIMMUNE PARAMETERS IN ATLANTIC SALMON (SALMO-SALAR) SMOLTS

This study was conducted to evaluate the effect of dietary iron level and form of ascorbic acid (AA) on growth, haematology, iron status, an tioxidant status and non-specific immunity in Atlantic salmon. Atlanti c salmon smelts were fed extruded fish meal diets with or without addi tion of 400 mg iron/kg as iron sulphate, and 150 mg/kg of two differen t chemical forms of ascorbic acid (ascorbic acid polyphosphate, AAPP o r ethyl cellulose coated ascorbic acid, AAEC) for 20 weeks. The experi ment was conducted as 2 x 2 factorial design. The basal diet contained 160 mg iron/kg. There were no significant differences in growth or mo rtality between the dietary groups during the experiment. Fish fed die ts without iron supplementation had significant reduced hepatic iron c oncentration after 16 and 20 weeks of feeding, compared to the iron su pplemented groups. Further, regression analyses of hepatic iron concen tration vs. weeks of feeding showed that fish fed diets supplemented w ith iron and AAPP maintained the hepatic iron concentration during the experiment, while the hepatic iron concentration was significantly re duced in fish fed diets supplemented with iron and AAEC. Supplementati on of AAEC gave significant reduced hepatic AA concentration after 4 w eeks of feeding the experimental diet compared to supplementation of A APP. Supplementation of iron had no effect on the status of AA. Furthe r, the haematological parameters were not affected by the dietary trea tments during the experiment. Iron supplementation as well as suppleme ntation of AAPP lead to a small, but significant, increase in head kid ney catalase activity after 20 weeks of feeding, while no significant effects were found in serum concentration of total protein, serum tota l antibody specific haemolytic complement activity, serum spontaneous haemolytic complement activity, serum lysozyme activity, head kidney l ysozyme activity, spleen lysozyme activity or spleen catalase activity . In conclusion, the antioxidant status was mainly a result of the for m and stability of dietary AA, and iron supplementation had no effect on the growth, haematology, antioxidant status or health of the fish. (C) 1998 Elsevier Science B.V.