The weather is 13 degrees. What is the reason why all the fish in the fish pond float on the water?

4-5 pm is usually the time when dissolved oxygen is the highest in a day. At this time, the fish floated to the surface for two reasons: 1. The fish in this pond are ill and need emergency treatment. It is recommended to find a fish doctor immediately. 2. The pond is seriously short of oxygen, which may lead to flooding, so it is necessary to rebuild the bottom quickly and increase oxygen-increasing equipment.

During the hot day, the water temperature will be stratified, the surface water temperature will be higher, and the downward temperature will not be high. ...