2. Usually there are many reasons for fish jumping out of the tank, which may be because the water quality is not good and needs to be changed to improve. It may also be because the dissolved oxygen in the water is low, and the fish will jump out of the tank because of lack of oxygen. In addition, some fish have the nature of jumping out of the water. For this kind of fish, there is often no good way but to add a lid to the top of the fish tank.