I have 3 danios in my community tank (20g). Two are zebra danios, one looks the same but has speckled dots instead of stripes. Anyway, two of the danios look normal, with slight bulges under their belly that looks normal. The third one (zebra) has no belly at all, his body is perfectly straight and long, and his tail droops. It makes him look very skinny, especially compared to the others. He also isn't very active, he just hangs out at the top corner of the tank. He has a nip out of his fin that wasn't there yesterday, so someone bugged him. I've noticed for a while that he was kind of long and skinny (kinda looks like an eel), but he was active and doing his thing until the last couple days when he started hanging out alone. Does this sound a little off?