| Bacillus substilis, photosynthetic bacteria and nitrifying bacteria are widely used for the improvements of water quality in aquaculture. Chaetoceros Lemmermann or Skeletonema costatum are basic diets for larval shrimp. This purposes of study were to examine the effects of individual species of the abovementioned algae,bacteria and algae-bacterial combination on water quality ,and the stress resistance and immunization capacity of Litopenaeus vannamei.Results are as follows:1.At a density of 3×103 cfu·mL-1, photosynthetic bacteria significantly(P<0.05) reduce the concentration of CODMn, NH3-Nt and NO2-N by 31.59%,43.42% and 52.20% respectively,when compared with the control group. The activity of alkaline phosphatase ( AKP) , peroxidase ( POD) , phenoloxidase ( PO) , superoxide dismutase ( SOD) , anti-bacterial enzyme(ABE) and bacteriolysis(BTY) of Litopenaeus vannamei increased by 31.92%, 72.29%, 55.56%, 31.61%, 39.07% and 69.51%, respectively. After 24 hours of cultivation under ammonia nitrogen , nitrite nitrogen,formaldehyde and potassium permanganate stress, the survival rate of the treatment groups increased significantly (P<0.05).Moreover, the survival rate of the treatment groups increased by an average of 18.67% and the weight gain increased by an average of 1.34 fold when compared with the control group.2. At a density of 1.25×104 cfu·mL-1, Bacillus substilis significantly(P<0.05) reduce the concentration of CODMn, NH3-Nt and NO2-N by 65.30% , 59.70% and 88.64% respectively when compared with the control group. The activity of AKP , POD, PO, SOD,ABE and BTY of Litopenaeus vannamei increased by 3.67, 1.64, 0.45, 3.06, 2.57 and 1.14 folds, respectively. After 24 hours of cultivation under ammonia nitrogen , nitrite nitrogen,formaldehyde and potassium permanganate stress,with the density of 1.25×104～1.25×106 cfu·mL-1 of Bacillus substilis,the survival rate of the treatment groups increase significantly (P<0.05).Moreover, the survival rate of thetreated groups increase by 10.00% and the weight gain increase by 2.44 folds when compared with the control group.3. At a density of 1.5×104cfu·ml-1,nitrifying bacteria significantly(P<0.05) reduce the concentration of CODMn, NH3-Nt and NO2-N by 48.59%, 46.69% and 57.70% respectively when compared with the control group. The activity of AKP, PO, POD and ABE of Litopenaeus vannamei increase by 82.33%, 24.00%, 84.32% and 14.17%, respectively. After 24 hours cultivation under ammonia nitroge , nitrite nitrogen, formaldehyde and potassium permanganate stress, the survival rate of the treatment groups increase significantly (P<0.05).Moreover, the survival rate of the treatment groups increase by 26.10% and the weight gain increase by 94.66% when compared with the control group.4.Chaetoceros Lemmermann is better than Skeletonema costatum in improving water quality.The most effective density of Chaetoceros Lemmermann in water quality improvement is 0.5×105cells·mL-1,with this density, the average concentration of CODMn, NH3-Nt and NO2-N of the treated groups decrease by 71.34%,43.14% and 26.42%, respectively.However,the most effective density of Skeletonema costatum is 0.2×105 cells·mL-1, with this density, the average concentration of CODMn, NH3-Nt and NO2-N of the treated groups decrease by 34.42%,32.92% and 23.60%, respectively.5.The most effective density of Chaetoceros Lemmermann in restraing increase of vibrio is 0.8×105 cells·mL-1,with this density,the average counts of vibrio decrease by 56.72% when compared with the control group. The optimal density of Skeletonema costatum is 0.2×105 cells·mL-1, with this density,the counts of vibrio decrease by an average of 53.36% when compared with the control group.6.Duncan multiple comparison display that the optimal density range of Chaetoceros Lemmermann effect Litopenaeus vannamei in resist ammonia nitrogen stress is 0.5×105～0.8×105 cells·mL-1,and the optimal density range of Chaetoceros Lemmermann in resist nitrite nitrogen,formaldehyde and potassium permanganate stress are 0.2×105～0.8×105 cells·mL-1.The optimal density of Skeletonema costatum in Litoenaeus vannamei resisting ammonia nitrogen stress is 0.2×105 cells·mL-1,in stress nitrite nitrogen is 0.2×105～0.5×105 cells·mL-1.Moreover,the density of Skeletonema costatum have insignificantly(P>0.05)effect in Litopenaeus vannamei resisting formaldehyde and potassium permanganate stress.7. Orthogonal experiment was used to construct algae-bacteria system.The best proportion among Chaetoceros Lemmermann,Photosynthetic Bacteria,Nitrifying Bacteria and Chaetoceros Lemmermann is 10:25:3:60.That is to say the optimal combination is 0.5×105,1.25×104,1.5×103 and 3×104 cfu·mL-1 ,respectively. This algae-bacteria system is more effective in improving water quality,straining multiplication of vibrio and enhacing stress resistance of Litopenaeus vannamei.Moreover,this algae-bacteria system is used in breading prawn of Litopenaeus vannamei that also achieve a perfect effect.
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