Effects of carbohydrate addition on Litopenaeus vannamei intensive culture in a zero-water exchange system

The present study investigated the effects of carbohydrate addition on the water quality, carbon/nitrogen ratios, densities of total bacteria, nitrogen cycle bacteria and zooplankton, and shrimp growth performance in a zero-water exchange system for Litopenaeus vannamei intensive culture. Sucrose was added as the carbohydrate into the water at five levels, i.e., 0, 25%, 50%, 75% and 100% of the theoretical adding quantity. Our results demonstrated that carbohydrate addition, especially 75% and 100% of the theoretical quantity significantly reduced the concentrations of total ammonia nitrogen and nitrite nitrogen during the late culture period in the water (P < 0.05). In addition, carbohydrate addition significantly increased carbon/nitrogen ratios and total bacterial densities of the water (P < 0.05), whereas did not affect those of the sediment on the whole. We also found that the densities of nitrogen cycle bacteria (ammonia-oxidizing, nitrite-oxidizing and denitrifying bacteria) in both the water and the sediment of the carbohydrate-added treatments were obviously affected compared to those of the control treatments. Zooplankton densities in the water were determined to be significantly increased by carbohydrate addition (P < 0.05). The parameters for shrimp growth performance including the yield, survival and feed conversion ratio demonstrated that 75% of the theoretical quantity was more suitable for L. vannamei culture. Conclusively, carbohydrate addition into zero-water exchange systems for L. vannamei intensive culture can effectively improve the water quality, bacterial activities and zooplankton growth, consequently resulting in the better growth performance.

► Carbon addition is beneficial to intensive shrimp culture without water-exchange.
► Carbon addition prevents the accumulation of TAN and NO2-N.
► Carbon addition improves C/N ratios in the water rather in the sediment.
► Bioactivities of bacteria, especially nitrogen cycle bacteria are increased.
► Carbon addition increases zooplankton density and shrimp growth performance.