Effects of dietary conjugated linoleic acid on growth, nutrient utilization, body composition, and hepatic lipogenesis in rainbow trout juveniles (Oncorhynchus mykiss)

Dietary conjugated linoleic acids (CLA) have been shown to alter growth rates and reduce body fat storage by altering the activity of key enzymes involved in lipid metabolism, in several species, but have not been evaluated in rainbow trout. A 12-week growth trial was conducted with rainbow trout juveniles, having an initial weight of 5.3 ± 0.03 g (mean ± S.D.). Fish were fed to satiation, twice a day, with diets containing graded amounts of CLA (0%, 0.5%, 0.75%, 1.0%, or 2.0%). At the end of the experiment, the daily growth index, feed intake, feed efficiency, and whole body composition were determined. The lipogenic activity of some enzymes (glucose-6-phosphate dehydrogenase, G6PD, EC 1.1.1.49; malic enzyme, ME, EC 1.1.1.40; and fatty acid synthetase, FAS, EC 2.3.1.38) was also measured in the liver. Further, digestibility of the diets was determined, using chromic oxide as inert tracer, and an automatic system for the faecal collection. No significant differences were detected (P > 0.05) in growth parameters, feed conversion, nutrient or energy utilization, body composition, or lipogenic enzymes activity among treatments. The results obtained in this experiment clearly suggest that CLA can be incorporated up to 2.0% in rainbow trout diets without any adverse effects on fish performance or feed efficiency.