The fish is just a symbol of their identity. Just the way anyone's car is a symbol of their identity. If it is overkill to express one's personality, then people should all dress in drab, identical clothing, have the same haircut, go to the same job, etc. What's wrong with being excited about your religion? It's an accomplishment, just like those "My daughter is an honor student" blah blah blah stickers... so what?