Why do goldfish always bang their heads against the side of bowl?

Goldfishes do not normally deliberately bang their heads against the sides of their bowl. If a goldfish appears to be engaging in this behavior the possible causes are:

1. They are trying to get your attention.

2. They are not getting enough oxygen and are coming to the surface for air.

3. They are stressed and trying to escape from their environment.

4. They have an injury or an illness.