Effect of dietary conjugated linoleic acid on muscle, liver and visceral lipid deposition in rainbow trout juveniles (Oncorhynchus mykiss)

Some of the conjugated linoleic acids (CLA), cis-9, trans-11 and trans-10, cis-12 isomers, may present a wide range of health benefits. Taking into account these beneficial effects and the relative low amounts of CLA in fish products, commercial diets for juvenile rainbow trout were supplemented with graded levels (0, 0.5, 0.75, 1 and 2%) of CLA. Duplicated groups of 5.3 g fish were fed to satiation, twice a day, over a period of 12 weeks with a CLA mixture, containing mainly the bioactive cis-9, trans-11 and trans-10, cis-12 isomers. The increase of dietary CLA levels did not affect growth performance, feed conversion ratio (FCR), hepatosomatic index (HSI) or viscerosomatic index (VSI) of the rainbow trout juveniles. Total lipids in muscle and liver were similar among treatments. In viscera, CLA supplementation reduced total lipids, but only the 0.5% CLA treatment differed significantly from the control. The fatty acid profile was affected by the dietary inclusion of CLA, resulting in a significant increase of the saturated and polyunsaturated fractions and a general decrease of the monounsaturated one, in both muscle and viscera. Nevertheless, in liver only fish fed 1% CLA had a significantly higher saturated fraction. The general decreases of monounsaturated fatty acid level in tissues with the saturated increase suggest a reduction of Δ-9 desaturase activity. CLA was deposited in all tissues and reflected the dietary CLA level. The highest concentration was attained when the 2% diet was used (6.9 g/100 g lipids in muscle). In conclusion, rainbow trout are capable of incorporating CLA in muscle, liver and viscera better than any other vertebrate, showing that this species is a potential route to increase human CLA ingestion.