Just thinking. If the rain influx was cold enough to displace water near the pond bottom and mix it into the water column ... and if the water was anoxic and laden with organics not fully decomposed ... the rain event might have created a low DO event. So part of what I am thinking is that some species are more resistant than others at surviving dips in DO. My impressions from study and personal experience is that the different species ordered from most risk of death to most probable survivors would go like this:

Blue Catfish, BG, GSF, GSH, CC, Gambusia.

If anyone sees any cracks in this order feel free to add your two cents. But if Blue Catfish and some BG/GSF succumbed then there is the possibility that the CC filled up on weakened and dead BG/GSF. Could possibly explain why the CC are not coming to feed. One way to test may be to fish for CC and remaining Blues with BG or GSF cut bait and to verify whether the proposition holds water. fowells, you need to do a little harvesting anyways so you could check stomach contents if you happen to catch any.