Just about any Tilapia will work for that zone. I'm in zone 9b and I have Blue and Nile tilapia alive and it has gotten pretty cold out here. I have an outdoor 700 gallon tank in the ground. The lining is black and it picks up a good bit of heat during the day, but I have never checked to see how much heat it loses at night. The tilapia are alive though!Originally Posted by green2go