To put a whole fish into the oven in its raw state is no trick. But to remove it cooked and whole from the oven to the platter requires a bit of skill. The simplest and easiest way follows.
Cover broiler rack with a sheet of foil. Find the holes in the broiler rack, then punch holes in the foil to match these places. The liquids from the fish as it bakes will drain into the broiler pan through the holes in the foil.
Coat the foil with oil. Set the whole fish belly-side down on the foil. Cover the dorsal and tail fins with foil to reflect the heat and prevent burning. Put a small ball of foil into the mouth of the fish. This keeps the jaws open; then when the fish is done the foil can be replaced with an olive or radish.