Saffron Fish Stew with White Beans

1 cup prechopped onion

1 teaspoon ground fennel

1/2 teaspoon ground coriander

2 garlic cloves, crushed

1 thyme sprig

1/2 teaspoon grated fresh orange rind

1/4 teaspoon saffron threads, crushed

1 1/2 cups water

1 1/2 cups clam juice

1 (14 1/2-ounce) can diced tomatoes, undrained

1/8 teaspoon salt

1 pound flounder fillet, cut into (2-inch) pieces

1 (14-ounce) can great Northern beans, rinsed and drained

Fresh thyme leaves