Conjugated linoleic acid in diets for juvenile Atlantic salmon (Salmo salar);: effects on fish performance, proximate composition, fatty acid and mineral content

We have examined the effects of different levels of dietary conjugated linoleic acid (CLA) on the growth and body composition of 0.7 g Atlantic salmon fry. Groups of fish were fed diets containing 0%, 0.5%, 1.0% or 2.0% CLA for a period of 12 weeks. The fish were weighed in bulk at start and after each 4-week interval, and samples were collected for analysis of the proximate composition, fatty acid composition and mineral composition. Growth rates were calculated, as were the fatty acid content in body burden increase (BBI) of lipid and the deposition ratio (R-D) of fatty acids. CLA did not have a significant effect on the growth rate or on the proximate composition of salmon fry, even though there was a trend (P = 0.08) towards higher final weight in the fish fed the 1% CLA diet. The fatty acid composition was strongly affected by diet. CLA was deposited in the fish, and dietary CLA also affected the deposition of other fatty acids. The R-D values of 14:0, 16:0 and 18:0 increased, while the R-D values of 16:1 and 18:1 decreased, in response to increasing levels of CLA in the diets. This suggests that CLA causes a reduction in Delta-9 desaturase activity. Dietary CLA caused a significant increase in the R-D values of total n-3 fatty acids, especially that of 22:6n-3. CLA also caused a higher concentration of phosphorus (P) and calcium (Ca), and a lower P/Ca ratio in the fish. The results show that dietary CLA may alter fatty acid metabolism and bone mineralization. (C) 2004 Elsevier B.V. All rights reserved.