Preheat oven to 350 degrees F.
Season pike liberally with salt and pepper. Melt butter in pan and sear both sides of fish. Remove from pan and set aside.
Add mushrooms, scallions, pepper, and paprika and cook over low heat. Add flour and make a roux. Whisk in stock by thirds and bring to a simmer. Whisk in sour cream and check seasoning.
Place fish back into the pan, cover, and roast in the oven 30 minutes or until fish is flaky.