Effects of dietary vitamin E on growth performance, body composition, antioxidant capacity, and some immune responses in Caspian trout (Salmo caspius)

This study was conducted to evaluate the effect of dietary vitamin E on growth performance, feed utilization, biochemical properties and some immune responses in Caspian trout, Salmo caspius. Six experimental diets were formulated with semi-purified ingredients supplemented with vitamin E in the form of DL-α-tocopherol acetate to provide the actual vitamin E concentrations of 4.9 (the basal diet), 8.6, 17.4, 35.4, 78.8 and 137.0 mg kg−1 diet, respectively. Each diet was assigned to three replicate groups of Caspian trout (initial average weight of 9.73 ± 0.34 g) for eight weeks. Weight gain ratio (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) were found to be significantly enhanced by increasing dietary vitamin E level and reached to the highest values in fish fed with 78.8 mg kg−1 vitamin E supplemented diet (P < 0.05). A significantly linear increasing trend was recorded in crude protein, fat content, superoxide dismutase (SOD) activity, liver vitamin E concentration, immunoglobulin M (IgM), and alternative complement activity (ACH50), while glutathione peroxidase (GPX) activity was linearly and quadratically enhanced in response to increasing dietary vitamin E supplementations (P < 0.05). There were also linearly and quadratically decreasing trend in alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT) activities as well as serum glucose (GLC) and malondialdehyde (MDA) levels by supplementing dietary vitamin E (P < 0.05). Analysis by the polynomial regression of SGR, GLC, and SOD activity against varying levels of dietary vitamin E revealed that the optimum dietary vitamin E requirements in Caspian trout were 79.44, 78.73, and 82.16 mg kg−1, respectively.