Urgent! Why does Mickey Mouse always jump out of the jar?

This phenomenon is mainly due to high fish density and lack of oxygen. Fish jump when they are uncomfortable, just like before it rains in the fish pond. In hot summer, oxygenation is necessary. It is suggested to reduce the number of fish or change to a bigger fish tank. It's not realistic to change the water pump, mainly because your fish tank is too small and the water pump is too big.