my Mollie lost his tail, What could have happened?

last night he was fine, this morning his back tail fin was half way gone. I've had him in the same tank with the same fish for about 6 months now and there hasn't been any problems at all. I have 2 suspects my betta and one of my angels. I know angels get along fine with mollies but one of my angels has always been bossy with the other fish, even the beta is afraid of him. but then again betas can be moody, but my beta has never done anything like this before. he usually sits at the bottom and comes up for air every so often. so who could it have been?

never mind I think I cought the cuplret red handed it was my betta... I just don't understand though, he was fine with the other fish for so long why all of a sudden? I turned the heat up in the tank recently but not by too much. At least I know when it's hotter out side I'm alot more craby, could it be the same with betas?

I'd bet on the angelfish. As they mature they become territorial and aggressive. Juvenile angelfish may get along fine with their tankmates, but adult angelfish are very effective predators. I like to keep them in a single species tank.

no I know it's the beta as I was watching the tank for awhile and he started nibbleing on my mollies fin. he was cought red handed (or in this case red mouthted). the mollie was just submitting which it think was the problem is that my mollie is too passive. and just let the beta do it to him. once I took the beta out my mollie started getting more comfortable and started swiming around instead of floating around in a submissive way. my angels never minded the mollies they always get along great, plus my angels are still about 4 months old. but that is good info to keep in mind for later.