Growth performance, carcass composition, hematological and biochemical indices of rainbow trout, Oncorhynchus mykiss juveniles fed diet containing different levels of vitamin premix

An 8-week feeding trial was conducted using a flow-through system to determine the effect of different levels of dietary vitamin premix on growth, carcass, hematological and biochemical indices of juvenile rainbow trout. Practical diets with six levels (0.00, 0.25, 0.50, 0.75, 1.00 and 1.25%) of dietary vitamin premix were fed to rainbow trout juveniles (mean initial weight 26.3±2.9g) at 3 replicates. Growth indices containing final weight, weight gain, body weight increase, feed conversion ratio, specific growth rate, condition factor and hepatosomatic index were not affected by dietary treatments. No mortality or deficiency signs were observed during the experiment. There was no significant difference in carcass proximate compositions. Hematological indices, including hematocrit, hemoglobin and the number of red blood cells were affected by dietary treatments, but the number of white blood cells was not affected. Biochemical indices containing cholesterol, total protein, and peroxidase did not differ significantly in fish fed the different diets, but significant difference was observed in triglyceride and alkaline phosphatase levels. Stress indices including cortisol, glucose and lactate levels showed significant difference among the treatments. Regarding to the obtained results, both nonsupplementation and excess supplementation of vitamin premix in the diet have some negative effects on rainbow trout. Thus, the appropriate level of vitamin premix should be used in the diets of this species.