I have 2 zebra danios and 1 male betta in my tank, and I just noticed that one of my zebra danios has had his fin bitten A LOT. My betta has fin rot, which he has had since the fish store, is it possible he could have passed it on one of my danios? Is it fin rot? I have a 7.5 litre tank, which I am told is too small for a zebra, could the biting be because of stress? Do I need to move them out of the tank? I don't want any of my fish to be biters, please help!