Take a look at this link and note that stress is a big factor.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=7;t=000295;p=1#000000

Then you can go to the second link and look at pics to see some examples. Note near the bottom of the first page of this link that there are 6 pages of pics.

http://www.ag.auburn.edu/fish/image_gallery/categories.php?cat_id=61&page=1