There are a number of key points to bear in mind when pan-frying fish on the skin.
Be sure the fish is ambient before adding to the hot pan.
If cooking straight from the fridge, the protein will set unevenly and it will be challenging to determine doneness, especially as fish has a relatively short cooking time.
2. The fat
To cook crisp-skin fish I use a small amount of ghee to begin the process, which I discard after two minutes of cooking and replenish with another small amount to finish the cooking.
3. The fish weight
I would find it difficult, if not impossible, to pan-fry or grill fish well without this piece of kitchen equipment, which can be found easily enough online.
These weights are not designed to be heated. When pan-frying a fish on the skin, the heat that's generated crisps the skin, which travels up through the muscle of the fish and sits on the face of the weight. This sets the top of the fillet very gently while forcing the skin to have direct contact with the pan.
By using a weight on thin to thickish fillets, you will be able to cook the fish from raw to cooked on the stove and rely less on the oven to finish cooking.
However, if cooking a very thick fillet, start by using the weight to crisp the skin, then once you see the first signs of colour, remove the weight and transfer to an oven to complete cooking.
An alternative to a fish weight would be to use a small, heavy-based saucepan filled with water, though this will be considerably more fiddly.
4. The heat
The heat we use to cook with is a target top gas stove, which is one large square of intense heat. I don't enjoy cooking over gas burners as a very high heat is needed to cook crisp fish skin and the flames of a gas stove can often flare up during cooking when moisture spits from the pan.
However, if you have a gas burner, don't tilt the pan too much when cooking fish as beads of moisture can hit the fat and cause flames to surround the fish.
Constant, uninterrupted heat is key to creating a crisp, glassy skin and pearl-like flesh – temperature control is everything.