What causes oxygen depletion in pond fish in winter?

This is because when the air temperature drops, in deep-water ponds, fertile-water ponds and high-density cage aquaculture waters, the water temperature at the surface is lower than that of the lower layer, and the specific gravity of the water is greater than that of the lower layer. Thus the cold surface water sinks and the warm lower-layer water rises, forming vertical convection of the water body. The water in the deep layer is low in oxygen or even anoxic, and the low-oxygen and anoxic water rises, causing severe oxygen depletion in the upper water body. On the other hand, this vertical movement of the water body accelerates the oxidative decomposition of organic matter such as leftover feed and feces deposited at the bottom of the pond, increasing the oxygen consumption within the water body. On yet another hand, in winter there is little sunlight, the photosynthesis of phytoplankton in the water is weak, and less oxygen is produced, resulting in insufficient dissolved oxygen in the aquaculture environment; combined with high stocking density, this makes it very easy for fish to gasp at the surface from oxygen deprivation or even die.

To prevent oxygen depletion in pond fish in winter, three measures can be taken: First, control the fish stocking density; especially in cage aquaculture waters, the area of the cages should be controlled within 3% of the total water surface, so as to ensure sufficient dissolved oxygen and avoid deterioration of the water body. Second, apply fertilizer scientifically; fertilization should be moderate and the method appropriate, to prevent the water from becoming too fertile and from being polluted. Third, harvest in a timely manner to reduce stocking density and lighten the load on the water body.