Design and experiment on crab ecological culture system using internal circulation and self-purification in a pond

Eriocheir sinensis (Chinese mitten crab) is one of the most important freshwater aquaculture species in China. Pond farming has widely been applied in several Eriocheir sinensis aquaculture modes. In this study, an improved Eriocheir sinensis, logical aquaculture system was proposed for better purification ability of pond water using the core technology of internal circulating and self-purification. Soft barricading was utilized to divide the aquaculture pond into two relatively independent functional areas, including the aquiculture and water self-purification areas. The specific procedure was as follows. 1) The air lifting and water pushing and jet device were designed to serve as the power source of water circulation in the aquiculture area. The air lifting and water pushing device pushed the water from the water self-purification to the aquiculture area, where the content of dissolved oxygen improved with a relatively low fluctuation of water temperature in the pond. The jet device created microfluidics in the dead corner of a pond or the area with dense aquatic plants. 2) The water self-purification area was designed to serve as the water circulation reverse-flow system, aiming at suspended solid filtration, physical absorption, sterilization, and water cooling in the backflow of internal circulation. 3) A field test was carried out in the Shanghai Baodao Crab Company to evaluate the ecological aquaculture system. The test pond with an area of 9 600 m2 was located at 3174N, 12123E. Two parts of a pond were divided into an ecological aquaculture system, including the aquiculture area of 8 644 m2 and the water self-purification area of 956 m2. The results were showed as following: 1) The flow rate of each air lifting and water pushing device was tested to be 187 m3/h. The pond water was exchanged more than twice a day. 2) The standard deviation of temperature fluctuation was lower than that of the traditional mode. The average value for equilibrium degree of water temperature was 0.893, 10.17% higher than that in the traditional mode with 0.811 equilibrium degree of water temperature. 3) The average value of dissolved oxygen in the deepwater layer (below 70 cm) was 4.498 mg/L, 18.57% higher than that in the traditional mode. 4) The average concentration of ammonia nitrogen was 19.2% lower than that of the traditional mode. Consequently, the water quality of the ecological aquaculture system was much better than that of the traditional mode. 200 crab samples (100 female crabs and 100 male ones) were randomly selected from the test and traditional pond (control group). The comparison result showed that the yield of crab increased 17.9% using the ecological aquaculture system, where the male crabs over 200 g increased 45%, and the female crabs over 150 g increased 35.0%. The finding can provide a great reference to Eriocheir sinensis aquaculture industry.