Docosahexaenoic acid in Arctic charr (Salvelinus alpinus): The importance of dietary supply and physiological response during the entire growth period

The aim of this 14-month feeding study was to investigate the effects of dietary docosahexaenoic acid (DHA) on tissue fatty acid composition, DHA retention, and DHA content per biomass accrual in muscle tissues of Arctic charr (Salvelinus alpinus). A control feed, formulated with a relatively high DHA inclusion level (F1), was compared with feeds containing gradually reduced amounts of DHA (Feeds F2, F3, and F4). Arctic charr were randomly distributed among 12 tanks and fed one of the feeds in triplicate. The DHA content within muscle tissues of fish fed diets F1 and F2 was generally higher compared to fish fed diets F3 and F4. However, there was an interaction between dietary DHA treatment and season, which resulted in fish muscle tissues having similar DHA contents irrespective of dietary supply during specific sampling periods. Although diets F3 and F4 contained ~4-fold less DHA compared to diets F1 and F2, the retention of DHA in dorsal and ventral muscle tissue was up to 5-fold higher relative to the diet content in fish fed diets F3 and F4. However, the difference among treatments was dependent on the month sampled. In addition, younger fish retained DHA more efficiently compared to older fish. DHA (μg DHA/g/day) accrual in muscle tissue was independent of somatic growth, and there was no difference among treatments. The results suggested that dietary DHA may be essential throughout the life cycle of Arctic charr and that the DHA content of muscle tissues was influenced by diet and metabolic/physiological factors, such as specific DHA retention during the entire growth cycle . Finally, this long-term feeding study in Arctic charr indicated a non-linear function in DHA retention in dorsal and ventral muscle tissues throughout the life cycle, which varied in its relationship to dietary DHA.