So, i was going to post this in the fresh water disease forum but decided that my fish weren't really sick so it didnt really belong there. anyways, i own some guppies and whenever I see a heavily pregnant female I remove her to a separate birthing room (a ten gal). Long story short, I owned this black female that I really liked and she was pregnant so I moved her to the separate tank (along with three other females). On the third day that they were in there, i saw the black female when I came to feed them at night. When I woke up to feed them, I didnt see her and only found out about 3-4 hours later that she died in a cave decoration that I kept in the tank. my conclusion is that she got trapped in the cave and didnt know to sink lower and exit through the exit. Obviously stress was a factor in her death but my question is if guppies need to breathe air, much like we do, in order to survive? normally, I would so say no to this idea but in my past experience, there was this one time when I put a pregnant female into one of those plastic breeder net/cages that traps fries at the bottom and prevents the female reaching them. when I returned from work I found most of the fries dead at the bottom of the net/cage (they were born while i was out). to get back to the point, my black female couldn't have been trapped inside the cave for more than 13 hours (the point from my last time seeing her and the time I discovered her body). Her body was deteriorated enough that when I scooped her up, her stomach was punctured and the the dead fries came out. Im not an expert but this suggest that she died in the first few hours after being trapped. she obviously didnt die from hunger and not from bad water, so is stress alone strong enough to kill a fish in only a few hours or did she really need to surface for air?