It is easy to overcook fish in the pan especially if you are new to pan-frying. Cook the fish on the first side for 3 to 4 minutes on medium heat reducing the heat as necessary to prevent them from burning. Then turn the fish over and cook another 2 to 3 minutes. Pro tip - depending on the thickness of the fish, each fillet should take about 3 to 4 minutes per side. The second side cooks faster.