Effects of zinc supplementation in diet on the immunity,Vibrio resistant ability,lysozyme mRNA and Toll receptor mRNA expressions in the white shrimp(Litopenaeus vannamei)

Experiments were conducted to study the effects of dietary zinc supplementation on the immune gene expression and immunity and disease-resistant ability of white shrimp(Litopenaeus vannamei).The shrimp were fed with 3 zinc methionine diets(supplemented at 0,50,150 mg Zn/kg diet respectively)respectively for 14 days.Then the expressions of Toll Receptor mRNA and lysozyme mRNA in gill and superoxide dismutase(SOD)activity and lysozyme(LSZ)activity in hepatopancreas,muscle and haemolymph were assayed respectively.The shrimp treated with different zinc diets were also challenged with Vibrio alginolyticus.The results showed that the zinc levels in hepatopancreas and muscle of shrimp significantly increased(P<0.05)as the dietary zinc increased.While the hepatopancreas accumulated more zinc than muscle.Compared to those of the shrimp in 0 mg Zn/kg and 150 mg Zn/kg treatments,the expressions of Toll receptor mRNA and lysozyme mRNA in gill of the shrimp in 50 mg Zn/kg treatment were significantly up-regulated.The lysozyme activities in muscle,hepatopancreas and haemolymph of the shrimp in 50 mg Zn/kg treatment were significantly higher than those in 0 mg Zn/kg treatment(P<0.05).The SOD activities in hepatopancreas and haemolymph of the shrimp in 50 mg Zn/kg and 150 mg Zn/kg treatments were also higher than those in 0 mg Zn/kg treatments(P<0.05).While the SOD activity in muscle of the shrimp treated with 150 mg Zn/kg was significantly higher than those treated with 0 mg Zn/kg and 50 mg Zn/kg respectively.The half lethal time and complete lethal time for the shrimp in 50 mg Zn/kg treatment were longer than those in 0 mg Zn/kg and 150 mg Zn/kg treatments after being challenged with V.alginolyticus.It is therefore suggested that compared to those in 0 mg Zn/kg and 150 mg Zn/kg treatments,the shrimp fed the diets added 50 mg Zn/kg(the content of zinc in diet was 73.25 mg Zn/kg)had improved immunity and Vibrio resistant ability.