I run a summer tub here myself. It is the dead of winter in this hemisphere so the fish are indoors now. At 37C, it is just too hot for any common fish to thrive. Unless you can get significant shade and cool that thing down, it is not a good place for any fish. On the other hand, if you can get the temperature to below about 30C consistently there are a few fish that could survive and thrive in it. I cool mine by two methods. First is the shade which helps a lot. The second method is to let water evaporate and provide cooling by doing so, just like perspiring helps. That is where my fountain / filter comes in. By spraying the water into the air, the water is cooled about 3C below the surrounding air temperature.
This is the tub in action.
You can make out the filter and pump in this picture.
This is the tub in action.
You can make out the filter and pump in this picture.