The fish weren't hibernating they were in shock. It is safe to drop the water temperature in your livewell 7-10 degrees. Anymore than that and you will chance putting them into shock.

Also the bags of ice you buy have chlorine and other chemicals in them that could harm the fish.

Next time take some water from the lake home in some of the empty soda/water bottles you have and freeze them. Better yet, add some Please Release Me or Rejevunate to the water before freezing. Then you've got ice from the lake thats been treated and can be added to the livewell.

Charlie