Combine first 8 ingredients in a Dutch oven; bring to a boil. Cover, reduce heat, and simmer 15 minutes or until potatoes are tender.
Place flour in a large bowl; gradually add 1/4 cup 1% milk, stirring with a whisk until smooth. Stir in remaining 1 1/4 cups 1% milk. Add evaporated milk to flour mixture. Stir milk mixture into potato mixture, and increase heat to medium-high. Cook 5 minutes or until slightly thick, stirring frequently. Add fish; cook 4 minutes. Stir in shrimp; cook 6 minutes or until shrimp are done. Serve immediately.