Whether tilapia can ever take cold winters depends on how many adaptations are built in to the organism. Anolis lizards, for example, developed a cecal valve in only 35 years after colonizing the Greek island of Lesbos, IIRC. Not remotely enough time for this to happen by random mutations, must have turned on a preprogrammed response to the island diet. Similarly, there is a seagull that develops an organ to rid itself of excess salt when it feeds in the ocean, but the organ disappears when it feeds in fresh water.
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