This is fascinating...

One of these stories reminds me of something I have heard (don't know how "urban legend" this is or no). The story goes that this one breed of fish is very fond of eating another smaller breed of fish. If you put them in a tank together, in little time, you will have no small fish left. But, if you put a piece of glass in the tank seperating the 2 breeds, the bigger fish will slam into the glass over and over until it gives up altogether. Then, when you pull out the glass, the bigger fish will *still* not go after the little fish, even though they swim all around them.