Conjugated linoleic acid in diets for large-size rainbow trout (Oncorhynchus mykiss):: effects on growth, chemical composition and sensory attributes

The effects of graded levels (0 %, 0.5 %, 0.75 and 1 %) of dietary conjugated linoleic acid (CLA) were assessed on 97 g rainbow trout. Fish were fed to satiation twice a day for 12 weeks. At the end of the experiment, all groups of fish weighed more than 250g and no significant differences were detected in growth performance, feed conversion, nutrient or energy utilisation or body composition between treatments. A decrease in liver lipid content resulted from including CLA and was accompanied by a reduction in malic enzyme activity. The muscle saturated acid and PUFA content did not vary between dietary treatments, despite the increasing concentration of stearic acid and CLA. In the liver, however, both fractions increased significantly with dietary CLA. Moreover, the MUFA decreased significantly in both muscle and liver. CLA was incorporated into tissue lipids, with levels in flesh (2-1-4.2%) being 2-fold higher than in liver (0-8-1.9%). In muscle, the percentage of cis-9,trans-11 isomer ranged from 39.5 % to 41.8 % and that of trans-10,cis-12 isomer from 31-4 % to 33-4 % of total CLA. The incorporation of CLA isomers in the liver varied with dietary treatment, and the cis-9,trans-11 isomer seemed to be more efficiently incorporated than trans-10,cis-12. Sensory data indicated slight-to-moderate differences between the trout fed with and without CLA. The present results suggest that 250 g rainbow trout can incorporate CLA in both muscle and liver, contributing to the production of a functional food.