As far as I know the only thing that can kill gambusia is eachother. Or anything that can rip them in half for that matter but that's besides the point. I had a tub pond of them outside, thought they all died of natural causes, left it out anyway so I had a partial rain/snow water pond ready for my next tubbing season. As of recently the weather has warmed up and I decided to go check on the ponds. To my surprise, there were a few gambusia up swimming frantically around the surface doing mating dances and fighting and all. The water temp at that moment was 47 degrees. Obviously since they overwintered they can go lower. Is there any recorded low for how low they can go?