During steaming, the water should be at a slow boil that generates a good amount of steam, but not so high that the water evaporates too quickly.
To check if the fish is cooked, insert a chopstick into the middle of the thickest part of the fish. If the chopstick pierces through the fish easily, it is usually fully cooked. Remove the fish.
Fresh seafood tastes better. Shop for fresh, sustainably sourced Giant Grouper or Dragon Tiger Grouper.