Clean, scale and top all the fish. Cut them into large pieces, leave the small ones whole. Bring 3 liters of water to a boil in a pot.
Peel the onions, 3 cloves of garlic, the leeks and the fennel. Wash the leeks and fennel, mince them. Chop the garlic and onions. Peel the tomatoes and crush them.
In a large casserole dish, put the onions, garlic, leeks, fennel, tomatoes, bay leaf, thyme, orange peel, saffron, salt and pepper. Add the fish, pour in 4 cl of olive oil and turn the casserole dish in all directions so that everything mixes and the fish soak up the different flavors.
Pour the boiling water over the fish and cook them over a very high heat for 5 minutes. A violent and brief boil should combine the oil and water. Lower the heat and simmer for 10 minutes. Adjust the seasoning, which should be well seasoned.