Don't feed Koi under 55o F unless you figure it's going to hang there a while.

There is a “temperature dynamic” regarding the feeding of fish. Fish are cold blooded. That means they are 'water temperature' if you were to touch them. They don't generate heat, and their metabolism is directly affected by water temperature. So when they are cold, they have a very slow metabolism. When they are hot, their metabolism is racing. Did you know that for every ten degrees increase in temperature, the metabolism of a cold-blooded organism doubles? It's a fascinating fact that you will be challenged to fit into a conversation with anyone. 

Koi that are fed in cold water are usually okay but there are a couple of circumstances that can be hazardous to Koi relative to cold water feeding. If you feed the Koi in cold water, and subsequent to this, the water temperature drops into the low forties, high thirties, the undigested food WILL damage the intestinal lining.

Also, in cooler water, say; under 65 Fahrenheit, you will notice that filtration bacteria associated with the "Cycle" will be less effective and so if fish are fed, be wary of accumulations of Ammonia and Nitrite by products.