Generally, the best types of fish to steam are not too large or too fatty.
Perforated pan, steamer or pressure cooker
A sharp knife
Lay the fish on the work-surface, hold it by the tail with one hand. Grip the knife in the other hand and scrape the fish starting from the tail towards the head. Once the fish is completely descaled, wash it under cold running water.
Using a sharp knife, cut the fish from the head to the middle of the belly. Carefully remove the guts.
Insert an index finger inside a gill and pull strongly to extract it completely. Then wash the inside and outside of the fish under cold running water.
Place the fish on the grill of a fish steamer with boiling water already inside. (You can add herbs to the water if you wish.) Cover and cook. The water should not touch the fish.
If you have a steam oven, place the fish in a perforated pan or and cook in a preheated oven (185-200°F). Cooking times vary according to the type of oven, the temperature and the size of the fish.
It is reccomended to check the internal temperature of the fish. (It should be 150°F.)
The empirical way to check if the fish is cooked requires a bit of experience judging the consistency fish with your fingertip. You can also poke the fish with a toothpick. If the toothpick is warm, the fish should be done.
Remove the fish from the oven, and let it cool before serving.
As an alternative
Steaming can be done with a pressure cooker or steamer. In that case, place the fish on a rack (or a small basket) inside the pot. Previously filled with water. Normally. The level of the water should not reach the rack with the food on it. Cooking times are significanly reduced when steaming under pressure because the temperature of the vapor is much higher. In addition, less soluble substances and primary nutrients in the food are lost when cooking with steam rather than boiling.