Milder weather question

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As I sit here in a stuffy office - full of people whoes only breath of fresh air they seem to take is the quick scurry between the carpark and their computer screen - gazing out the window towards the Severn I wondering if this spell of milder weather has any affect on fishes behavior and there prey.

Is it the case that as soon as the real cold weather arrives they think "right, that's winter" and disapear for good until Spring or will a spell of milder stuff bring the fish back in?