actually, I would go with standard
goldfish. comets or shubunkins. They are hardier than koi, some of them are pretty darn pretty...(especially the shubunkins). I'm in Arizona, and my pond (about 180 gallons) gets about 85 - 90 degrees farenheit in the summer. I have several goldfish and a shubunkin. I also have two chinese algae eaters and one pleco to help get rid of the algae. I have several pond lillies that provide shade for the fishies so they don't get sunburn. I also have a couple dozen mosquito fish - I love to watch them eat the dried tubifex worms I supplement feed them with. They act just like mini pirahna - tearing apart the little cubes!