3. The influence of water temperature, salinity and weather on dissolved oxygen

In spring, the surface water temperature rises with the rise of atmospheric temperature, and there will be obvious water temperature stratification. Under the influence of wind in sunny weather, waves will be formed on the water surface, which will increase the contact area between water and air, and dissolved oxygen can be supersaturated at a depth of 0 to 1 meters. When the water level deepens further or encounters cloudy and rainy days, especially heavy rain or rainstorm days, a large amount of fresh water will be injected into the aquaculture pond to form a freshwater layer with low salinity. . Especially at night, plankton moves downward and vertically to the bottom, coupled with the oxygen consumption of the sediment, the dissolved oxygen at the bottom of the pond continues to decline. This situation is more obvious in summer, and the lack of dissolved oxygen at the bottom of the pond will be further exacerbated. , so as to form a stable hypoxic layer, ammonia nitrogen and hydrogen sulfide gas harmful to the sea cucumber will be continuously produced, and it is easy to cause the sea cucumber to be hypoxic and suffocate to death.

4. Effects of Apostichopus japonicus excrement, bait and biological debris on dissolved oxygen

Apostichopus japonicus excrement, residual bait and biological debris accumulate at the bottom of the pool for a long time. These organic matter are eutrophicated and oxidized and decomposed at the bottom of the pool, which will quickly consume a large amount of dissolved oxygen in the water. The oxygen consumption of organic matter and the viscosity of water further lead to the inability of oxidative decomposition to proceed well. At this time, soluble ammonium salts and non-ionic ammonia (NH3) coexist in the water body in a certain proportion, but the proportion of the two varies with the water temperature. The changes of pH value and pH value are different. Among them, ammonia (NH3) has strong toxicity to Apostichopus japonicus, and it is easy to cause death of sea cucumber poisoning.