I have had a few guppies in the past, and had a such an enjoyable experience with them. I decided to start a new tank, and just put three new male guppies in the tank. There are no other fish in there. I just walked back to the tank, and noticed that one of guppy's tail has a piece missing from it. I can only assume one of the other guppies did it! The other guppies I had were so peaceful and non-agressive, I just can't believe this happened. The injured fish seems to be OK, he's swimming around and eating. I observed the fish for several minutes and did not see any aggressive behavior. Is there anything special I should do to make sure the injured fish is OK? If I do find one of the fish to be aggressive, should I try to return him to the store? I really do not enjoy aggressive fish. I had a friend who had Tiger Barbs and all they did was try to kill each other all the time. I do not want that kind of tank. Any info you have would be greatly appreciated. Thanks.