Peel and chop the potatoes into even-sized chunks. Place into a saucepan, cover with water and boil for 15 minutes or until a fork can easily press through the potato.
Lower the heat to a simmer and continue simmering for 5 minutes. Remove the pan from the heat and set aside (covered) for 10 minutes. Gently remove the cooked fish and break into large pieces.
In a large bowl, place the mashed potato, fish pieces, egg, butter, chives, lemon zest, sour cream, salt and pepper. Mix together with a spoon until completely combined and the fish has flaked into smaller pieces.