Light a charcoal grill. Mix together the salt and juice in a casserole that is large enough to hold all the ingredients and bring to the boil.
Place the shell and fish bones in a fish basket and grill for around 4-6 minutes on both sides until they start to turn brown.
Grill the tomatoes, fennel and celeriac until tender and the tomatoes start to collapse. Place on one side and keep the fennel and celeriac warm.
Place the bones and shell in a saucepan and boil in the stock for 10 minutes. Sieve the stock into a blender along with the tomatoes. Blend until the soup is smooth and pour back into the (cleaned) saucepan. Heat and add salt and pepper to taste.
Season the pieces of fish with salt and pepper and grill for a few minutes on each side until they are nice and brown and the meat starts to fall away when you prick it with a fork.
Arrange the fish and vegetables decoratively in bowls. Pour the hot soup over them and serve.