| 2 tablespoons unsalted butter |
| 1 medium onion, finely chopped |
| 2 stalks celery, finely chopped |
| One 14 1/2-ounce can chicken broth |
| 2 medium potatoes, peeled and cut into 1/4-inch cubes |
| 1 pound halibut fillet, cut into bite-size pieces |
| 1 pound uncooked medium shrimp, peeled, deveined, and halved lengthwise |
| Two 12-ounce cans evaporated milk |
| 2 cups chopped fresh clams |
| 24 fresh oysters, shucked, with liquid reserved |
| 1 tablespoon chopped fresh thyme leaves |
| 1 tablespoon chopped fresh parsley, for garnish |