The effects of combined phytogenics on growth and nutritional physiology of Nile tilapia Oreochromis niloticus

This study investigated whether dietary supplementation of phytogenic compounds limonene and thymol had synergistic or additive effects on growth and selected nutritional physiology pathways in Nile tilapia. A 63-day feeding experiment was conducted using fish of 1.5 +/- 0.0 g ( +/- standard error) fed on a commercial diet coated with either 0 ppm limonene and thymol (control), 400 ppm limonene (L), 500 ppm thymol, (T) or a combination of 400 ppm limonene and 500 ppm thymol (LT). Final fish weight (FW) was significantly improved to similar extents by diet LT (16.7 +/- 0.3 g) and L (16.6 +/- 0.4 g). Dietary thymol alone and the control did not enhance FW (15.0 +/- 0.4 g and 13.7 +/- 0.4 g respectively). Dietary thymol had shown a strong tendency to improve somatic growth (P = .052). The analysed candidate genes involved in the pathways of nutrient digestion, absorption and transport (muc), lipid metabolism (lpl), antioxidant enzymes (cat) and somatotropic axis growth (igf-I) were also up-regulated to similar extents in Nile tilapia by diet L and LT (P < .05), above the regulation observed with the diet supplemented exclusively with thymol. This suggests lack of synergistic or additive effects on growth and nutritional physiology pathways when limonene and thymol are supplied in the diet.