i don't think you're supposed to put beta fish in the same tank...or at least you're supposed to have dividers...they will inevitably attack and kill each other

ick....

betta fish are a ton of fun and very relaxing to watch. one i had in college was suicidal and would jump out of his bowl at random times (like the goldfish in <a href="http://www.youtube.com/watch?v=2T9dUBO4pv0">Amélie</a>... only i wouldn't scream like that). i saved his life many times but one day he jumped out while i was in class. :(

the male that i thought was the prettiest was lost due to a female betta beating him up... i had read that betta fish were easy to <a href="http://www.ask-the-vet.com/breeding-betta-fish.htm">breed </a> and thought i would give it a go. i kept the fish separate to make sure both were healthy first. but she must have thought he was an ugly fish and was offended by his advances. i removed him from her tank but the injuries he sustained caused him to die a few days later.

moral of the story female betta fish are indeed mean. your fish may have killed her roomie before deciding to eat her. all fish will eat their dead roomies i think it's to keep the tank clean and so the bacteria doesn't build up. but you may be looking at a case of MURDER!