What causes a fish to bloat?

[T-Rexx]

The other day I noticed one of my Glow Light Tetras had REALLY bloated. His eyes were bulgey and he blew up like a balloon! The next day the poor thing was found dead, but I don't know what could have caused it. I worry it may happen to my other fish as well. Is it possible that the aquarium salt I put in the tank about 2-3 weeks ago may have caused it?

 

[rich311k]

It could be too much food or he could have picked up a disease. Tropical fish are quite susceptible to it and feeding lightly really does help control it.