Summary:
The effects of dietary lipid oxidation on fish are diverse and contradictory. In this study, herring oil was oxidized to five different levels (peroxide values (POV): 20.44, 182.97, 56.12, 33.27 and 0.00 meq kg- 1) and used to formulate five experimental diets. Juvenile Arctic charr (Salvelinus alpinus, mean body mass ± SD: 2.41 ± 0.11 g) were reared on the five diets for 67 days. In another experiment, juvenile Nile tilapia (Oreochromis niloticus) (1.71 ± 0.40 g) were reared on three diets formulated with oxidized oils having POV of 19.55, 447.27 and 32.72 respectively, for 90 days. Growth responses were monitored in quadruplicate groups of 60 individuals of Arctic charr and 100 for Nile tilapia, respectively. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were only studied in Arctic charr.
At the end of the study, the Arctic charr group reared on a diet with oils in the primary oxidation state had significantly lower body mass and specific growth rate, but higher hepatosomatic index compared to the rest of the groups. The activities of CAT and GPx increased with dietary lipid oxidation while that of SOD remained fairly stable. In Nile tilapia, both final body mass and condition factor were significantly lower in the group fed fresh oil than in the groups fed oxidized oils. Fillet lipid content decreased with lipid oxidation while ash and protein did not differ amongst tilapia groups. The results suggest that Arctic charr are more susceptible to lipid oxidation than are Nile tilapia. These differences may be the result of species differences in tolerance to oxidized lipids, variable lipid intake or access to vitamin E / tocopherol in feed.