Effect of dietary flaxseed oil level on the growth performance and fatty acid composition of fingerlings of rainbow trout, Oncorhynchus mykiss

This study evaluated the suitability of flaxseed oil as a source of supplemental dietary lipid for fingerlings of

rainbow trout (Oncorhynchus mykiss). Triplicate groups of the 30 fingerlings held under identical culture conditions

were fed twice daily by iso-nitrogenous, iso-calorific and iso-lipidic diets for 8 weeks. Experimental diets consisted of

30.2% protein, 18.6 kJ g-1 energy and 16.5% lipid from fish oil (FO), flaxseed oil (FxO) and 1:1 blends of the oils

(FFxO). Moisture, ash, protein, final body weight, specific growth rate, weight gain, feed conversion ratio, survival

and hepatosomatic index were not affected by treatments but the percent of lipids was significantly highest in fish

fed the flaxseed oil diet (FxOD). The condition factors of fingerlings reared on FxOD and fish and flaxseed oils diet

(FFxOD) were significantly lower than those fed the fish oil diet (FOD). Protein efficiency ratio (PER) was significantly

higher than those fed the FOD and FFxOD. Whole body fatty acid compositions mirrored those of diet treatments.

The highest amounts of highly unsaturated fatty acids (HUFAs) were detected in fish fed 100% FO, which was

significantly different from other treatments. In all treatments polyunsaturated fatty acids/saturated fatty acids

(PUFAs/SFAs) and n-6/n-3 ratios were higher than 0.45 and lower than 4, respectively. Present results indicate the

fingerlings can be reared on diets in which FO has been replaced with FxO, with no significant effects on fish

performance.