Interaction between two dietary levels of iron and two forms of ascorbic acid and the effect on growth, antioxidant status and some non-specific immune 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, antioxidant status and non-specific immunity in Atlantic salmon. Atlantic salmon smelts were fed extruded fish meal diets with or without addition of 400 mg iron/kg as iron sulphate, and 150 mg/kg of two different chemical forms of ascorbic acid (ascorbic acid polyphosphate, AAPP or ethyl cellulose coated ascorbic acid, AAEC) for 20 weeks. The experiment was conducted as 2 x 2 factorial design. The basal diet contained 160 mg iron/kg. There were no significant differences in growth or mortality between the dietary groups during the experiment. Fish fed diets without iron supplementation had significant reduced hepatic iron concentration after 16 and 20 weeks of feeding, compared to the iron supplemented groups. Further, regression analyses of hepatic iron concentration vs. weeks of feeding showed that fish fed diets supplemented with iron and AAPP maintained the hepatic iron concentration during the experiment, while the hepatic iron concentration was significantly reduced in fish fed diets supplemented with iron and AAEC. Supplementation of AAEC gave significant reduced hepatic AA concentration after 4 weeks of feeding the experimental diet compared to supplementation of AAPP. Supplementation of iron had no effect on the status of AA. Further, the haematological parameters were not affected by the dietary treatments during the experiment. Iron supplementation as well as supplementation of AAPP lead to a small, but significant, increase in head kidney catalase activity after 20 weeks of feeding, while no significant effects were found in serum concentration of total protein, serum total antibody specific haemolytic complement activity, serum spontaneous haemolytic complement activity, serum lysozyme activity, head kidney lysozyme activity, spleen lysozyme activity or spleen catalase activity. In conclusion, the antioxidant status was mainly a result of the form 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.