For the barbel from the oven, preheat the oven to approx. 180 °C convection oven. Form a boat for the gutted, descaled barbel with enough aluminum foil.
Season the belly of the fish with butter (more or less depending on the size), salt, pepper, chopped garlic and thyme.
Also season the outside according to taste and place the fish on the boat in the oven for about 30-45 minutes, depending on the size of the barbel. Remove the barb from the oven and serve.