Effects of dietary thymol-carvacrol on growth performance, hematological parameters and tissue composition of juvenile rainbow trout, Oncorhynchus mykiss

Growth performance, carcass quality, survival and hematological responses of Oncorhynchus mykiss juveniles (initial weight 8.4 +/- 0.1 g) fed diets containing thymol-carvacrol powder at the levels of 0, 1.0, 2.0, 3.0 g kg(-1) were tested. Thymol-carvacrol powder originated from Origanum vulgare, a Mediterranean plant, added to diets. Each diet was fed to triplicate groups of fish for 45 days. Fish fed diets containing thymol-carvacrol had significantly higher final weight and growth than the control group. Food conversion ratio in fish fed diets containing 2.0 and 3.0 g kg(-1) thymol-carvacrol was statistically better than in other treatments. Survival was not different among all treatments. The number of lymphocytes increased when thymol-carvacrol was used at higher levels. Furthermore, whole body lipid content was higher in fish fed 1.0 and 2.0 g kg(-1) thymol-carvacrol than the other groups, but body protein in the group fed 3.0 g kg(-1) was higher than in other groups. Also, body ash in control and 1.0 g kg(-1) was higher than in other groups. Whole body dry matter was not affected by dietary treatments. These results indicated that dietary administration of thymol-carvacrol can influence some growth, hematological parameters and tissue composition in rainbow trout juveniles.