Total replacement of fish oil by vegetable oil with a return to fish oil in Caspian Sea salmon (Salmo trutta caspius) 1: Growth performance, flesh fatty acid profile, and lipid metabolism

The effect of complete substitution of vegetable oils (cottonseed, soybean and grape seed) and a
return to fish oil diets on growth parameters, survival and metabolism of free fatty acids in the diet
of fish in the Caspian Sea, was investigated. Four experimental diets containing 100% fish oil,
cottonseed oil, grape seed oil and soybean oil were fed to triplicate group of fingerlings (initial
weight 3.6 g) for 60 days. No significant difference was detected for weight gain,
specific growth rate and survival. Fillet fatty acid composition was analyzed and the results showed
that fillet fatty acid composition was highly affected by dietary fatty acid profile. The highest
accumulation rate of linoleic acid and linolenic acid was observed in the fish fed vegetable oil based
diets. The results showed that feeding vegetable oil based diets stimulated elongation and
desaturation pathway of C18 PUFA in fingerlings. However, the highest amount of EPA, DHA
arachidonic acid (AA) was observed in fish oil based diet. At the end of the second period, after
return to fish oil based diet, muscle fatty acid composition (total saturated fatty acid, linoleic and
linolenic acid) of the fish fed previously vegetable oil based diets were still different to those fed
fish oil based diet.