When I came home from school one day, my betta was laying on it's side on the bottom of the tank, still breathing, when I tried to scoop him up, he tried swimming, but nose dived to the bottom. I decided to put him out of his misery, but when I got him out, I noticed his anal fin was missing. I don't think that the other fish (platies, corys, and an alge eater) would've done it, and he didn't have any sign of fin rot that morning, so I'm wondering what could've happened? 
