Effects of Dietary Cottonseed and/or Canola Oil Inclusion on the Growth Performance, FA Composition and Organ Histology of the Juvenile Rainbow Trout, Oncorhynchus mykiss

This study aimed at demonstrating the effects of total and 50% dietary fish oil replacement by cotton seed and canola oils and a mixture of these vegetable oils (VOs) on growth, tissue fatty acid composition and histology of digestive organs in the juvenile rainbow trout for 84 days. Five iso-nitrogenous and lipidic diets were formulated to replace dietary fish oil (FO) totally by cotton seed oil (CSO), canola oil (CO) and an equal or 50% FO/ 50% VO mixture. Duplicate groups of 50 fish (~15 g) were fed two times daily to apparent satiation. Growth performance, feed efficiency and viscerosomatic index were not influenced by dietary treatments (P>0.05). However, hepatosomatic index was significantly higher (P<0.05) in fish fed with CSO and CSO50/CO50 diets. Fish fed CSO or CO diets had significantly lower levels of n-3 highly unsaturated FAs and increased levels of 18:2n-6 in the whole body FA composition (P<0.05). Furthermore, liver had significantly higher levels of docosahexaenoic acid and arachidonic acid than those in the fish whole body. Results suggest that the 50% replacement of dietary fish oil by cotton seed oil and canola oils in equal amounts could be possible without compromising growth and overall well-being in the juvenile rainbow trout.