Just a few days ago I added 8 Zebra Danios and 8 White Skirt Tetras to my 60 gallon tank of 8 Albino Corys.
One of the Danios is chasing all of the other Danios around. In fact it is bossy - but this only started today and the bloated Danio has been bloated since I got it. I thought it was a normal female trait. However the fish keeps floating up easily, but manages to stay down at the same level - leading me to conclude it might be swim bladder disease. Google turns up inconclusive. (Maybe it's pregnant?)
I've ruled out almost all disease, including dropsy, because it looks normal, just bloated.
I feed the tank freeze-dried brine shrimp and bloodworms, daphnia, sinking wafers, fish flakes, and that's all. The Danios 90% of the time eat what's on the surface, which is just blood worms and daphnia. Brine shrimp as well, but the tetras usually get that.