Effect Of No Carbohydrate Addition On The Function Of Bioflocs In Shrimp Culture Water And Analysis Of The Function Of Two Cultivable Bacterial Strain

The accumulation of harmful nitrogen compounds such as total ammonia nitrogen（TAN）and nitrite nitrogen（NO₂^–-N）in the water seriously affects shrimp health in aquaculture,and therefore effective control of them is of great significance.Biofloc technology（BFT）promotes the growth of heterotrophic bacteria in the culture water by adding carbohydrates to adjust carbon nitrogen ratio,which efficiently improves the circulation of nutrients,such as carbon,nitrogen and phosphorus,and reduces the accumulation of TAN and NO₂^–-N in the pond water.However,is it necessary to add carbohydrates through the whole process of BFT?Do all the dominant cultivable strains in the bioflocs have the function of removed TAN and NO₂^–-N?A comparison experiment was designed to explore the effects of stopping brown sugar addition on water quality and nitrogen budget in an established shrimp BFT culture system,including brown sugar addition group（BS）and no brown sugar addition group（NBS）.Furthermore,the strains of OB1 and B1 selected in the shrimp BFT culture water earlier in our research group,were analyzed the function of removing inorganic nitrogen and phosphorus under different salinity and p H conditions.The results obtained in this study are as follows:（1）The concentrations of TAN and NO₂^–-N in BS and NBS groups were both at low levels.At the end of the experiment,TAN was 0.05 mg·L^–1 and 0.03 mg·L^–1 for the BS and NBS groups,respectively;while NO₂^–-N was 0.38 mg·L^–1 and 0.26 mg·L^–1 for the BS and NBS groups,respectively.The analysis of nitrogen budgets reveals that nitrogen input was mainly from feed,accounting for 78.8%,while nitrogen output mainly turned into total nitrogen（TN）.The TN of pond water in the BS and NBS groups accounted for 45.06%and52.55%,respectively.The harvested shrimp accounted for 21.49%and 25.43%of nitrogen output in the BS and NBS groups,respectively;whereas nitrogen utilization efficiency of the feed in the two groups was 18.14%and 23.14%,respectively.It suggests that stopping brown sugar addition did not affect the removal of TAN and NO₂^–-N by biofloc in the water of the established shrimp BFT culture system.（2）The cultivable strain OB1 could reduce the concentrations of TAN,NO₂^–-N,nitrate nitrogen（NO₃^–-N）,TN,phosphate phosphorus(PO₄^3–-P)by 85.87%,approximately 100%,100%,39.82%and 77.79%,respectively in aquaculture water.The removal of inorganic nitrogen and phosphorus by this strain was significant.Strain OB1 could grow at p H 8.0-10.0 and salinity 22-40,and its bacterial quantity could reach 10⁸ cells·m L^–1.However,it could not grow at salinity of 4,and grow slowly at p H of 6.0.（3）The cultivable strain B1 could increase the concentration of TAN by 61.02%,while it had no significant effects on the concentrations of NO₂^–-N,NO₃^–-N and TN in the water.This strain had no nitrification function.Strain B1 could grow at p H 6.0-10.0 and salinity 4-40,and its bacterial quantity could reach 10⁸ cells·m L^–1.