Feed intake and absorption of lipid oxidation products in Atlantic salmon ( Salmo salar ) fed diets coated with oxidised fish oil

Two questions were asked in the present study; does Atlantic salmon taste and discriminate against oxidised feed and are lipid oxidation products absorbed from the intestine. In Experiment 1, a control diet, a medium oxidised diet and a highly oxidised diet were prepared (TBARS levels: 34±5, 61±4 and 76±2 nmol g −1 , respectively). The control diet was marked with holmium and the experimental diets with europium. Each of the experimental diets were fed together with the control diet (1:1) to Atlantic salmon in duplicate tanks in one meal to satiation and the stomach contents were analysed for the lanthanides. The fish discriminated slightly against the highly oxidised diet, but not against the medium oxidised diet. In Experiment 2, Atlantic salmon cannulated through the dorsal aorta were fed control and oxidised feed (TBARS: 71±5 and 204±18 nmol g −1 ) and blood samples were collected regularly over a nine days period. On day 9, the fish were sacrificed, and samples of muscle, liver, intestinal tissue and contents were taken and analysed for oxidation products, and vitamins C and E. Plasma TBARS increased 3-4 fold in response to the oxidised diet and there was a slight increase in muscle and liver TBARS. The data on peroxide value (PV) in the tissues showed large variation, but no differences between the groups were detected. PV and TBARS in the contents of the large intestine increased 7- and 1.6-fold, respectively, in response to oxidised feed. There were no differences in levels of vitamins C and E between the groups. It seems that Atlantic salmon feed quite well on oxidised feed and that aldehydes, here represented by MDA and measured as TBARS, are absorbed from the intestine. The question as to whether lipid hydroperoxides are absorbed is unanswered due to the large variation in tissue PV. On the other hand, animals in general seem to be protected from absorption of lipid hydroperoxides and we hypothesise that similar mechanisms are active in Atlantic salmon.