The influence of temperature, dietary polyunsaturated fatty acids, α-tocopherol and spermine on fatty acid composition and indices of oxidative stress in juvenile Arctic char, Salvelinus alpinus (L.)

Juvenile Arctic char, Salvelinus alpinus (L.), were fed two levels of polyunsaturated fatty acids (PUFA) (5.5 or 2.5% of diet (37 or 16% of lipid respectively)), alpha-tocopheryl acetate (70 or 300 mg kg(-1) diet) and the antioxidant spermine (0 or 250 mg kg(-1) diet) in a 3x2 factorial design and analysed for tissue fatty acid composition and indices of oxidative stress. The effect of temperature was evaluated by first maintaining the fish at 12 degrees C for 70 days and then 0.6 degrees C for 71 days. Liver and muscle fatty acid compositions were significantly influenced by the fatty acid compositions of the feed, although extensive modification of some fatty acids took place prior to deposition in the tissues. Maintaining char at low temperature increased liver PUFA content particularly in fish fed the low PUFA diets while no major changes were seen in muscle. Tissue alpha-tocopherol deposition was mainly influenced by dietary alpha-tocopheryl acetate. Dietary spermine had no influence on tissue levels of spermine. Dietary manipulation had no major influence on haematology and blood chemistry. High dietary PUFA increased the content of thiobarbituric acid reactive substances (TBARS) in both liver and muscle. Neither alpha-tocopheryl acetate nor spermine influenced tissue TEARS content. Lowering the environmental temperature influenced several parameters including haematology, blood chemistry and muscle spermine content, but none were related to diet. It is concluded that Arctic char is tolerant to a wide range of dietary content of PUFA (16 to 37% of lipid) and alpha-tocopherol (70 to 300 mg kg(-1)), and that spermine offers no further protection against oxidative stress. It is suggested that toxic levels of PUFA is related to the amount in dietary lipid where more than 50% of lipid may be harmful to the fish.