Improved fillet quality in harvest-size Atlantic salmon fed high n-3 canola oil as a DHA-source

Abstract

New sources of the very long-chain n-3 polyunsaturated fatty acids (n-3 VLC-PUFA) are needed for sustainable growth of salmon farming. In recent research high n-3 VLC-PUFA canola oil has shown promise as a safe and effective source of docosahexaenoic acid (DHA) and other n-3 PUFA in small Atlantic salmon. To study its long-term effects on performance and fillet quality under realistic farming conditions, a 12-month feeding experiment was carried out with Atlantic salmon growing to harvest weight (4.7 kg) in triplicate sea water cages. The fish were fed three diets containing graded inclusion levels of high n-3 canola oil resulting in levels of dietary DHA (22:6 n-3) of 4.0% (Standard; STD), 6.6% (Medium; MED) and 8.3% of total fatty acids (HIGH) and total EPA + DHA of 6.4, 9.1 and 11.0% of total fatty acids, respectively. The STD diet was considered to represent current commercial practice. There were no significant differences between the dietary groups in overall fish growth and weight at harvest, and no differences were seen in feed conversion ratio. Tissue FA-profiles mirrored the diets, giving increased DHA, EPA (20:5 n-3) and ALA (18:3 n-3) with increasing inclusion level of high n-3 LC-PUFA canola oil. Dietary inclusion of n-3 canola oil had no effect on muscle astaxanthin concentration, but instrumentally measured redness, yellowness and chroma increased with n-3 canola oil inclusion, suggesting a positive effect on colour via effects on muscle structure or composition. The prevalence and severity of dark melanin spots in the fillet was significantly reduced by increased inclusion level of n-3 canola oil. The prevalence of severe spots (score ≥ 2), average score and number of affected muscle segments were all lower in MED and HIGH, compared to STD.In conclusion, high n-3 canola oil is an efficient source of DHA and other n-3 fatty acids for harvest-size Atlantic salmon. Increased dietary supply of DHA and other n-3 PUFA, above minimum requirement levels for DHA, improved fillet pigmentation and reduced fillet melanin spots, without compromising fish growth.