ARCTIC CHAR (SALVELINUS-ALPINUS) AND RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) DIFFER IN THEIR GROWTH AND LIPID-METABOLISM IN RESPONSE TO DIETARYPOLYUNSATURATED FATTY-ACIDS

Juvenile Arctic char (Salvelinus alpinus) and rainbow trout (Oncorhync hus mykiss) were fed one commercial and three casein-based diets varyi ng in amounts of 18:2n-6 and 18:3n-3, two polyunsaturated fatty acids (PUFA), for 12 wk at 10 degrees C. Both species on the diet without PU FA had lower specific growth rate (SGR) but higher percentages of live r neutral lipids and 20:3n-9 in liver polar lipids than those fed high PUFA content or commercial diets. Regardless of the amount of 18:3n-3 in the diets, the percentages of 20:3n-9 and 20:3n-9/22:6n-3 in liver or muscle polar lipids were significantly lower in char than in trout ; values in trout were lower than reported in other studies. These fin dings question the use of 20:3n-9/ 22:6n-3 as an indicator of essentia l fatty acid status for both species, Different levels of 20:3n-9, 22: 6n-3, and other PUFAs in tissue polar lipids of the two species sugges t that Delta 6 and/or Delta 5 desaturases are less efficient in char. While trout fed test diets had slightly less 20:4n-6 than wild trout, char had 1/10 less 20:4n-6 in muscle polar and total lipids than wild char, suggesting that char may require n-6 and n-3 PUFA in their diet for optimal performance.