Pierce potatoes with a fork. Arrange potatoes in a circle on a paper towel in bottom of microwave oven. Microwave at HIGH 10 minutes, rearranging potatoes after 5 minutes. Wrap potatoes in a towel, and let stand 5 minutes. Peel and cube potatoes; set aside.
Combine onion and next 14 ingredients (onion through bay leaf) in a 3-quart casserole; stir well. Cover with casserole lid, and microwave at HIGH 10 minutes, stirring after 5 minutes. Stir in potato, shrimp, and fish. Cover and microwave at HIGH 3 minutes or until fish flakes easily when tested with a fork. Discard bay leaf.