FWIW, I switched tilapia suppliers to a supplier in Ohio this year. The supplier that I had last year said they were pure blues but when the water temp dropped after stocking them in customer ponds, they majority of them died when the water temp dropped to 63°F. That tells me that they are NOT pure blues. This year I had Tilapia surviving in 54°F water from the new supplier. I also saw a much better FA control with the tilapia from the new supplier - they were supposed to be a 50/50 mix from both suppliers, but with the old supplier, I didn't see the amount of tilapia nests in the pond that I did this year.
Like the OP, I have not seen any small Tilapia that have died due to cold water temp. The smallest Tilapia that I have seen is around 10" long.
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