Effect of different levels of vitamin E on performance and some blood parameters of Caspian trout (Salmo caspius )

This study investigated the effects of different levels of vitamin E on growth performance and blood indices of Caspian trout (Salmo caspius) juveniles. Six diets with different levels of vitamin E including 0, 10, 20, 40, 80 and 160 mg kg-1 were prepared. The actual amounts of vitamin E in diets were determined using high performance liquid chromatography and were as follow: 4.9, 8.6, 17.4, 35.4, 78.8 and 137.0 mg kg-1. In total, 360 fish (initial mean weight of 9.32±0.34 g) were randomly distributed in 18 cylindrical tanks (20 fish per tank) with the working volume of 900 L. Each tank was randomly assigned to each of the experimental diets with 3 replications. The fish in each tank were fed with the respective diets for eight weeks and finally their growth indices and blood parameters were evaluated. The results showed that the final weight, daily growth coefficient and feed efficiency ratio of fish increased linearly (p<0.05) and quadratic (p<0.05) with increasing the vitamin E levels and reached the highest value in fish fed with 78.8 mg kg-1 vitamin E. Significant linear (p<0.05) and quadratic (p<0.05) increases in red blood cells (RBCs) and white blood cells (WBCs), hemoglobin content and hematocrit percentage were also determined by increasing in dietary vitamin E concentration. The percentage of neutrophils in fish blood reached the lowest level after feeding with the highest amount of vitamin E (137.0 mg kg-1 vitamin E) while the highest percentage of lymphocytes was recorded in fish fed with 78.8 mg kg-1 vitamin E. The findings of the present study showed that vitamin E could improve the performance and blood parameters of Caspian trout. The best level of vitamin E was estimated to be 82.16 mg kg-1 based on the daily growth coefficient and 102.98 mg kg-1 according to WBC number.