Goldfish just need a little clear water to stay alive. Mine are in 18" ponds and our freeze depth is 18". I only had to borrow a dog bowl heater once though.
The fish in Ken's pond would be dinner at my house. I tried to buy a Tilapia once but its illegal to own them unless you have a permit. The fish was gorgeous - all orange and green stripes! But the man said he would have to kill it before he could sell it.
