Here is what I believe....the fish does not know they are in a tank. They think the entire world is under water. They can see out and do not understand why they cannot swim into the middle of the living room. They know there is some kind of barrier stopping them from going any further, and they want out. The reason I believe this is pretty simple. I had a very aggressive Red Parrot Cichlid. This fish was very playful and would swim right up to you when you came near the tank. However, if I was standing in another room and the fish was able to see me, she would keep head butting herself against the glass to try to get to me. One day she just jumped right out and I had to scramble to get her back into her tank.
thats true but it allso could be the water level is to hi