When you can take a fork and the fish meat is flaky, its done. All meats should be cooked with at least 350 degrees in order to kill all bacteria. Answer, 03.21.10: To prevent bacterial growth, fish should be cooked TO an internal temperature of 145 degrees F and held for at least 15 seconds. It can be cooked AT whatever temperature you like. Always check the temperature in the thickest part of the fish.