| Apostichopus japonicus is one of the most important aquaculture species in China and pond culture is the primarily culture method. In the process of pond aquaculture, with the extension of the aquaculture period, organic fertilizer, residual bait, phytoplankton debris and excrement of aquaculture species in the water will be deposited in a large amount at the bottom of the pond, which will not only lead to the decline of water quality, but also cause a large number of toxic substances in the sediment, which will seriously affect the output of sea cucumber. In recent years, a water plowing operation mode has emerged during sea cucumber culture in Liaoning and Shandong Provinces, to control the water quality and pond sediment. However, the water plowing technology and environmental improvement mechanism are still unclear. A 48-days water plowing experiment was carried out in the sea cucumber culture area in Liaoning Province. The low-frequency group (water plowing once every 8 days), high-frequency group (water plowing once every 4 days) and control group (no water plowing) were set up. Through short-term continuous tracking and long-term regular monitoring, the changes of physicochemical factors such as chemical oxygen demand, phosphate concentration, redox potential and sulfide content in the water and sediment of the culture pond were analyzed. The results showed that the turbidity of water in the experimental groups were 4.16 ± 0.39 NTU, which was significantly higher than that in the control group at two days after water plowing operation; On the fourth day, the concentration of ammonium nitrogen and nitrite nitrogen in the experimental groups decreased by 88.9% and 75.0%, respectively, which was greater than that in the control group. After 31 days of water plowing, the concentrations of phosphate and nitrite nitrogen in the pond water of the low-frequency group and the high-frequency group were significantly lower than those of the control group, and the content of organic carbon in the sediment was also significantly lower than that of the control group (P < 0.05). After 47 days of water plowing, DO in pond water of low frequency group and high frequency group increased by 4.2% and 3.8%, respectively, but was lower than of the control group (37.7%). Conversely, COD increased by 21.4% and 21.8%, respectively, exceeding the control group (9.9%). The phosphate concentrations increased by 125.0% and 100.0%, respectively, yet were still lower than the control group (183.3%). ORP of sediments increased by 67.6 mv and 82.3 mV respectively, which were significantly higher than that of the control group (31.3 mV); The sulfide content in sediments decreased by 6.1% and 7.9%, respectively, while that in the control group increased by 298.4%; The proportion of Vibrio in sediments decreased by 2.5% and 7.1%, respectively, while that in the control group decreased by 1.8%. The results show that regular water plowing operation can conducive to keeping the water inorganic phosphorus at a low level, effectively inhibit the increase of organic carbon and sulfide content in sediments, significantly improve the ORP of sediments, and effectively reduce the proportion of Vibrio in sediments, thus the water plowing operation could improve and repair the aquaculture pond environment. Compared to the low-frequency group (water plowing once every 8 days), the high-frequency group (water plowing once every 4 days) exhibited more pronounced environmental regulatory effects. However, given that frequent aquatic tillage may lead to a slight decrease in DO, an increase in COD, and higher aquaculture costs, the optimal tillage frequency should be adjusted based on specific conditions, including pond water temperature, dissolved oxygen concentration, and the degree of sediment pollution and aging. The research results provide data reference for the development of water plowing technology and its application and promotion, and also lay the foundation for the in-depth explanation of its environmental improvement mechanism, the construction of disease prevention and control technology, and the realization of healthy culture of sea cucumber A. japonicus. |
