Batter fried fish is best done in a large commercial fryer which allows the fish to swim freely off the bottom of the fryer in a surplus of oil throughout the cooking. For successful batter frying at home you need to approximate this situation by using much smaller pieces of fish, and not over crowding the frying pan. For this reason you should cut the fish into narrow strips, just long enough to fit into your pan or fryer.
There are a few general rules to follow when deep-frying:
1). The oil temperature needs to stay at, or above 350° F throughout the cooking time, so start with the oil a little hotter to allow for some temperature drop when adding the cold fish.
2). Always deep-fry foods is small quantities so the pot is never crowded. Introducing a large amount of food at once lowers the oil temperature immediately. Maintain about two thirds of the oils surface area free.
3). Use a high quality, edible oil such as canola or soy oil, and throw it out after use. The oil should be at least twice as deep as the foods being fried. Be very careful to dry the fish before battering. This will keep spattering to a minimum. Above all be very careful!
Follow these rules and batter frying will produce moist fish inside a greaseless crisp crust. The fish actually steams inside a sealed shell, much like being baked in clay. The traditional beer batter is the
stuff of fish and chips while tempura is a much lighter approach.