Use equal parts butter and vegetable oil for successful pan-frying. Season and coat the fish first and ensure the butter is foaming before adding fish.
Place the fish, skin-side down, in foaming butter and oil. Fry for 5 minutes then turn the fish over.
Fry the fillets for another 3-5 minutes, until golden brown. Insert a Fork into the thickest part of the flesh - it should feel firm and be opaque throughout.