Actually I have goldfish in the galvanized tank at the barn. It is in full sun, all day, in Texas. Yes the water gets warm, but the fish do fine. I think in these large tanks that are meant to provide livestock water the temperature doesn't get as hot as you'd think and I think feeder goldfish aren't very delicate about their living conditions. At least that's been my experience. If the water is allowed to get low, then raccoons and possibly some birds may extract them. No aerator. I used to worry about it, but they do fine without it. Eventually they get pretty large. Sometimes they commit suicide by jumping out. I have to watch when I'm deliberately letting it overflow to skim trash and algae off the top. Another metal trough is primarily in the shade. Both those are growing green algae, but this one is in shade about 1/2 day. It's the newest. If I can catch any fish in there, I'll relocate them or put them in a rubber trough until I get this one coated. It has to be in this location to catch runoff from the roof, so moving it isn't an option. The fish are there to help with mosquito control and they do a lot better job of doing that they are credited with.
