I saw this phenomenon once in a very small non-maintained pond (1/16 acre?). The CC had very large heads compared to their body. The pond did not seem to be overpopulated because catching was difficult whether LMB or CC. I don't recall ever catching any pan fish. My assumption was that they had a severe lack of food sources and FA was kindof like when the fridge and cabinet gets bare and it's time to have some bran flakes with Koolaid.
