Effects of zinc sources and levels on growth performance, antioxidant indices and body composition in juvenile tilapia (Oreochromis niloticus × O. aureus).

A feeding experiment was conducted to study the effects of zinc sources and levels on growth performance,antioxidant indices and body composition in juvenile tilapia (Oreochromis niloticus×O.aureus).One thousand and eighty fish with (2.98±0.02) g initial body weights were divided into 9 groups with 4 replicates of 30 fish in each replicate.Nine groups fed control diet and eight experiment diets (zinc sulfate or zinc methionine,zinc additions were 10,20,30 and 60 mg/kg,respectively) during 8 weeks feeding trial.The nine groups were named C0,Zn-10,Zn-10,Zn-20,Zn-30,MZn-10,MZn-20, MZn-30 and MZn-60,respectively.The results showed that,compared with control group,the weight gain rate was increased significantly (P0.05) and feed conversion ratio was decreased significantly (P0.05) in Zn-60 and MZn-60 group.The activities of superoxide dismutase and total antioxidant capacity in liver in MZn-20 group was the highest,and significantly higher than those in control group,Zn-10 and Zn-60 groups (P0.05).The activity of catalase in liver in MZn-20 group was significantly higher than that in Zn-30,Zn-60 and MZn-60 groups (P0.05).Compared with control group and adding zinc sulfate groups,contents of crude protein in muscle were significantly increased,while content of crude lipid in muscle were significantly decreased by the supplemental zinc methionine (P0.05).Compared with control group, content of crude lipid in muscle was decreased in Zn-20 and Zn-30 groups ( P0.05),while content of ash in muscle was increased in Zn-10 group (P0.05).With the increasing of dietary zinc levels,condition factor was decreased and then increased, and the lowest level were found in Zn-20 and MZn-30 group which were significantly lower than that in control group and other experimental groups (P0.05).Compared with the control group,adding zinc to diets improved hepaticsomatic index and showed a significant increase in Zn-30 and MZn-60 groups (P0.05).Intraperitoneal fat index in MZn-60 group was higher than that in control group.In conclusion,adding 60 mg/kg zinc into practical diet of tilapia could improve growth performance,and the zinc methionine had the same effect as zinc sulfate;adding 10～20 mg/kg zinc into practical diet of tilapia could increase the antioxidant capacity and muscle composition,and zinc methionine was better than zinc sulfate.