Effect of dietary zinc oxide nanoparticle on leukocyte properties of rainbow trout (Oncorhynchum mykiss)

The effect of zinc oxide nanoparticle as a mineral supplement in the diet on the white blood cells of rainbow trout was investigated in this research. Eight hundred specimens of rainbow trout fry (17.22±5.41 g) were randomly distributed in 18 experimental tank (six treatments each with three replications). The basal diet was prepared without zinc supplementation and used for the negative control treatment. Other experimental diets were prepared by adding 10, 30, 50 and 70 mg/kg of zinc nanoparticles and 70 mg of zinc sulfate (positive control) to each kg of the basic diet. Blood samples were taken from the fish at the end of the experiment to check the number of white blood cells and their differential count. After two weeks of adaptation, the fish were fed for 8 weeks with the diets corresponding to each experimental treatment. Blood samples were taken from the fish at the end of the experiment to check the number of white blood cells and their differential count. The results showed that nano zinc oxide has a significant effect on the leukocyte count with the highest number of 178,000±22,000 No. mm-3 in fish fed diet supplemented with 50 mg kg-1 Nano ZnO, which was significantly more than their number in fish fed with basic diet (p<0.05). Furthermore, fish fed diet supplemented with 50 mg kg-1 Nano ZnO diet had the highest lymphocytes percentage of 72.21±0.13%, while the lowest percentage of neutrophils was also found in fish fed diet supplemented with 50 mg kg-1 Nano ZnO. However, the actual number of neutrophils in the blood of fish in this treatment was 4.5 folds more than those in the negative control treatment. Findings of the present study showed that zinc oxide nanoparticles have a significant effect on the leukocyte properties of rainbow trout.