Arctic charr, Salvelinus alpinus (L.), weighing 1.6 g, were fed either commercial or one of 12 semipurified diets containing different concentrations and types of n-3 and n-6 polyunsaturated fatty acids (PUFA). The effects of dietary composition on growth, feed efficiencies, hepatosomatic indices, liver DNA and RNA concentrations and RNA/DNA ratios were investigated. The lowest growth occurred in charr fed diets deficient in PUFA and increasing dietary 18:3n-3 from 0.1 to 2.0% led to improvements in specific growth rates and feed efficiencies. The level of dietary 18:3n-3 required for adequate growth appears to fall within 1.0-2.0%. Dietary 22:6n-3 was more effective for growth enhancement than dietary 18:3n-3 and dietary 18:3n-3 was more effective than dietary 18:2n-6. No significant differences in growth and feed efficiency were found for charr fed diets containing combinations of 2.26-2.82% 18:3n-3 and 0.56-0.70% 18:2n-6 or 2.0% 18:3n-3 only. This implies that dietary 18:2n-6 has a minimal effect in the presence of adequate amounts of dietary 18:3n-3. DNA concentrations were lower in livers from fish fed diets containing less-than-or-equal-to 1.0% n-3 PUFA and this suggests histological and biochemical changes. However, a higher DNA concentration was found in charr fed the PUFA-free diet. Hepatosomatic indices were correlated with DNA concentrations for all casein-based diets. RNA concentrations in livers appeared to be correlated to anabolic events and RNA/DNA was of little value as an indicator of growth.
