Heat 2 tablespoons (30 ml) of the oil in a heavy 4- to 5-quart (4- to 5-L) saucepan or shallow casserole. Add the mussels and cockles or clams, cover, and steam over medium heat until they open, about 10 minutes.
Remove the mussels and cockles from the pan with a slotted spoon, place in a bowl, and cover. Add 4 cups (1 L) of the fish stock and the fennel, carrots, and wine to the saucepan and bring to a simmer, add the shrimp. Cook about a minute, until the shrimp turn pink, then remove them with a slotted spoon. Place in a dish and cover.
Add the Salmon and bass to the pan, cook about 2 minutes, turn the pieces of fish, then return the shrimp, mussels and cockles to the pan.
Add the scallions and season the stock with salt and pepper.
Add the beans, bring to a simmer, and, if necessary, add the additional stock.
Stir in the remaining olive oil and serve in shallow bowls.