Investigation of effects of dietary organic and inorganic zinc forms on some enzyme, hormone and bone mineral level in rainbow trout (Oncorhynchus mykiss W., 1792)

In this study, the effect of dietary zinc at inorganic forms (zinc sulphate and zinc oxide) and organic forms (zinc picolinate and zinc methionine) on blood glucose level, plasma and liver malondialdehyde concentrations, blood and liver superoxide dismutase and serum alkaline phosphatase activity, insulin and insulin like growth factor-I (IGF-I) levels, and bone mineral composition in rainbow trout (Oncorhynchus mykiss) was evaluated. For this purpose, four different diets (D1= zinc sulphate; D2= zinc oxide; D3= zinc picolinate and D4= zinc methionine) were prepared at the zinc level of 30 mg/kg diet. Each diet was assigned to three replicate groups of 30 experimental fish (initial body weight = 50 ± 1 g) for 3 months. Results showed that the blood glucose and the plasma and liver MDA levels were lower in the groups treated zinc picolinate (D3) and zinc methionine (D4) in organic form when compared with the groups treated zinc sulphate (D1) and zinc oxide (D2) in inorganic form. The blood and liver SOD activities, the serum alkaline phosphatase activity and the plasma IGF-I level were higher in the groups treated zinc picolinate (D3) and zinc methionine (D4) in organic form when compared with the groups treated zinc sulphate (D1) and zinc oxide (D2) in inorganic form. No statistically significant difference was found between the insulin levels of groups treated zinc in organic and inorganic form. The bone zinc, iron, copper, calcium, and phosphor concentrations did not change with organic or inorganic zinc treatment. In conclusion, it can be said that zinc picolinate (D3) and zinc methionine (D4) seems to be more bioavailable than zinc sulphate (D1) and zinc oxide (D2) for rainbow trout.