Re-evaluating the dietary requirement of EPA and DHA for Atlantic salmon in freshwater
2020
Qian, C. | Hart, B. | Colombo, S.M.
The requirement for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is recommended at 0.50–1.0% of the dry diet for juvenile Atlantic salmon (Salmo salar). Current commercial aquafeed formulations for Atlantic salmon tend to contain a physiological excess of these fatty acids. The aim of this study was to re-evaluate the EPA and DHA requirement by Atlantic salmon parr in freshwater since it was determined 20 years ago, and feed formulations and salmon production have changed. This study evaluated the effect of different dietary levels of EPA and DHA (0.25 to 2.0%) on growth performance, overall health, and whole-body EPA and DHA content. Salmon (initial weight 22.6 g ± 1.2) were fed four levels (0.25, 0.5, 0.75 and 2%) of EPA + DHA diets for 6 weeks in freshwater at 12 °C. Diets were fed to triplicate tanks, with 20 fish per tank. There were no mortalities throughout the trial and fish nearly doubled their weight after 6 weeks. Categorically, there were no discrete significant differences in growth performance among treatments after 6 weeks. However, weight gain was exponentially related to diet EPA + DHA levels (p < .0001; r² = 28.3%), and the feed conversion ratio was inversely related. In both cases, these relationships suggested that the asymptote is reached between 0.25% and 0.5% dietary EPA + DHA. Whole body DHA and EPA showed positive linear relationships with diet DHA (p < .001; r² = 88.7%) and EPA (p < .001; r² = 92.9%). Based on growth performance and whole-body fatty acid content, salmon fed a diet containing 0.50% EPA + DHA diet exhibited similar growth performance and haematocrit with control diet (2%). Therefore, 0.5% is considered the lowest required EPA + DHA level for Atlantic salmon parr in freshwater in this study.
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