ANTIOXIDANT STATUS AND IMMUNITY IN ATLANTIC SALMON, SALMO-SALAR L, FED SEMI-PURIFIED DIETS WITH AND WITHOUT ASTAXANTHIN SUPPLEMENTATION

Parr of Atlantic salmon, Salmo salar L,., were fed semi-purified diets supplemented with 60 mg astaxanthin kg(-1) and without astaxanthin supplementation for 10.5 months. The astaxanthin concentration in the non-supplemented diet was analysed to be 6.0 mg kg(-1). The growth of the fish was significantly affected by the dietary treatment. The mean daily weight gain in the groups fed the supplemented diets was 0.39% throughout the period, whereas the groups fed the non-supplemented diet had a mean daily weight gain of 0.18%. The dry matter and fat content were significantly higher in fish fed the supplemented diet. The astaxanthin concentration in the muscle of fish fed the astaxanthin-supplemented diet was 2.7 mg kg(-1) versus 0.3 mg kg(-1) in the non-supplemented fish. Antioxidant vitamins in the muscle (retinol, alpha-tocopherol) and liver (retinol, alpha-tocopherol and ascorbic acid) were two to 20 times higher in the fish in the supplemented group, suggesting antioxidant sparing effects. Blood haemoglobin and immunological parameters tended to be higher in fish fed the low astaxanthin diet although the difference was not significant. However, the resistance to challenge with Aeromonas salmonicida was higher in fish fed the astaxanthin supplemented diet. This may be due to a difference in weight at the time of the challenge which, in turn, may have influenced the body composition and smoltification of the fish. A relationship between dietary astaxanthin concentration and antioxidant status in both liver and muscle was observed, and this may also have had an influence on the observed differences in blood parameters and disease resistance.