I added one ADF into my betta tank few days ago. They were doing great. But I noticed today that Burt (my male Betta) was swimming funny. After careful examination, I noticed that Burt's left pectoral fin is mysteriously "missing".
It doesn't look like it's been ripped out or anything like that since you can see it sort of tucked right next to his body.
From the front view, you can see that left fin is not opened at all.
What must I do to help him heal? Have you heard of AFD attacking and hurting bettas? You think it's caused from fighting? Or he scrapped himself against a filter or something?