Growth performance, hematology and immunological parameters of rainbow trout, Oncorhynchus mykiss, fed with diets containing different levels of vitamin E and folic acid

This study was conducted to evaluate the effects of dietary levels of vitamins E (25, 30 and 35 mg kg^-1), Folic Acid (1.5, 2 and 2.5 mg kg^-1) and their combination on the growth performance, hematological and immunological parameters of rainbow trout, Oncorhynchus mykiss. Each diet was fed to rainbow trout in triplicate to apparent satiation four times daily for 8 weeks. At the end of the feeding trial, the final body weight (FBW), total length (TL), feed conversion ratio (FCR), specific growth rate (SGR) and survival rate were significantly affected by treatments and the fish fed with the diet containing 35 mg kg^-1 vitamin E plus 2.5 mg kg^-1 of folic acid had higher values than those fish fed with the other diets. The results also indicated that hematocrit (Ht), mean corpuscular volume (MCV) mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) were significantly influenced by the treatments. Lysozyme and immunoglobulin (IgM) concentrations were significantly influenced by the dietary treatments, fish fed with the diet supplemented with 30 mg kg^-1 of vitamin E plus 2 mg kg^-1 of folic acid and unsupplemented diet had higher concentrations than those fish fed with the other diets. The findings of this study suggested that trout requires 35 mg kg^-1 vitamin E and 2.5 mg kg^-1 folic acid for it’s normal growth and physiology