Overall, fillet
fatty acid composition was reflective of dietary concentrations. Fillets
from all treatments were enriched in EPA and DHA relative to dietary
levels, indicating selective retention of these fatty acids as is typically
observed in fish (Trushenski et al., 2006). The DHA:EPA ratio in fish
fillets was similar among all treatments except for the FM20 group,
which was significantly higher. This difference can be largely explained
by differences in dietary fatty acid profile: levels of EPA were the lowest
in the FM20 feed, whereas dietary DHA was more similar among FM replacement diets, causing the FM20 to have the highest dietary DHA:EPA
ratio, which was reflected in the final tissue content. In all treatments,
fillet SFA decreased relative to dietary content, which could indicate
that these fatty acids were being catabolized as an energy source,
resulting in more efficient tissue deposition of LC-PUFA (Trushenski
et al., 2013). Total fillet n−3 fatty acid and LC-PUFA levels decreased
with increased FM replacement and were significantly different from
fillets in fish fed the FM100 diet. However, the content of LC-PUFA in
fish fed the FM replacement diets still contained 70 to 80% of these
fatty acids found with the FM100, which may still be enough to ensure
adequate nutritional value for the consumer