Removal of persistent organic pollutants from Atlantic salmon (Salmo salar L.) diets: Influence on growth, feed utilization efficiency and product quality

Atlantic salmon were fed diets with fish oil, either normal (control group) or cleansed for persistent organic pollutants (POPs) as the sole lipid source from smolt stage to harvest size. The POPs were removed using short-path distillation, aided by a working fluid, and were highly efficiently removed resulting in low dietary levels. Each diet was fed to fish in four cages, 5 × 5 × 5 m, and the fish were fed ad libitum by aiming at least 10% over feeding every day. Although the growth rate was low during the first months of the trial, the growth rate was good in total, from sea transfer to harvest size. The fish fed the diet with the cleansed oil grew significantly better than the control fish in 1 of the 5 periods. Feed conversion ratio (FCR) was significantly lower for the cleansed oil group for 2 of the 5 periods, as well as the total trial period. Nutrient digestibility was measured when the fish were around 1 kg and at termination of the study, and there were no significant differences between the dietary groups. There were no significant differences in dress out loss and condition factor, and hepatosomatic index was found to be significantly higher for the control group at the last sampling. Colour was measured by using DSM Salmofan at four points on the fillet as well as in the Norwegian Quality Cut, and found to be significantly higher for the control fish in one intermediate sampling. At the last sampling, there was however a tendency of higher colorization for the cleansed oil group. For fillets sampled at the termination for quality assessments, there were only minor differences in muscle pH, firmness, colour and consumer test. The muscle pH was significantly higher and muscle firmness tended to be higher for the cleansed oil group. The levels of POPs in fillets were highly significantly lower in fish fed diets with the cleansed oil. In conclusion, none of the parameters measured in the present study indicate any negative effects of the cleansing process in Atlantic salmon from smolt stage to harvest size. On the contrary, the study suggests positive effects on growth, feed utilisation efficiency and product quality.