I have a frat of 9 guppies in a 20 gallon. All params have been fine, tank is cycled. So far so good. One of my guppies was really really fat so I decided to fast the tank for just three days. I come back to examine and all the guppies look fine except the really fat one is fatter on one side and is a bit bent. Is this TB? And if so, is the best course of action euthanasia?