In the house I recently sold I built an outdoor pond. I stocked it with koi and a bunch of goldfish. I named all the fish. The fish were keeped in the upper pond as I had designed it to be the deepest with the lower section a bog for growing water plants. Well one day I went out there and about 75% of the fish were gone, except for parts of fins and heads and stuff like that. The racoons had found my pond! I built a cover out of cedar and steel wire mesh that I keeped on it from then on. About six months later I was draining the lower pond to remove and clean the filter and lo and behold there was one of the goldfish! He must have taken a trip over the waterfall and had lived in the lower section without being feed for six months! He had grown a bit and his new name was "Die Hard"! So my point is that these are hardy fish. I never took them out of the pond in the winter and at times the water temp can't be much above freezing. I just stop feeding them when the water temp dips below 50 F.