Tropical fish thrive between 25C and 27C. They can tolerate lower and higher temps, but 40C would kill them in short order. Aquarium chillers do exist and are adjustable for temperature. There are also some homemade designs out there. Here is one I found...

https://www.thespruce.com/diy-do-it-yourself-aquarium-chiller-2924600

Good luck - I hope you can set up an aquarium! They are really rewarding.