I keep fish tanks and the size of the tank may have a little to do with it. Although I don't trust bait shops to properly take care of their tanks and disease is probably prevalent, a general rule of thumb on fish tanks is one inch of fish per gallon. The biology of the tank/filter can't keep up with much more than that and rapid changes occur that can kill most of the fish. I did a similar experiment with some leftover crawfish from a boil in my 125 gallon tank. Most of them died within a few weeks, but they were very stressed in that bag before that and very overcrowded in my tank (there were 50 or so). I did have a few hearty ones last much longer once they established their territory, but they still ultimately died within a few months.
