Effects of dietary fatty acids on growth, feed efficiency and liver RNA and DNA content of Arctic charr, Salvelinus alpinus (L.).
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 <- 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.