I noticed two days ago that one of my 5 rosy tetras just got really bloated. There is no sign of illness on the scales or any other sign of illness (i.e. behavioral) but when I look at the fish head on, he is probably 2-3x wider than the other tetras of similar overall size. I say he, but have no clue what sex it is. Basically the fish looks and acts healthy except for the bloating. Any ideas?