How long to pan fry fish

The flake test. Slide the tip of a knife or a fork into the thickest part and twist it a quarter turn. Cooked fish comes apart into flakes along the lines of connective tissue with almost no pressure, and the flesh inside has gone from glassy to solid. Fish that is not ready resists the twist and still looks wet and shiny in the middle. Give that another minute and check again.

Two causes, and they usually arrive together. The pan was not hot enough when the fish went in, and the fish was moved too early. A fillet grips the metal while the surface protein is still raw and releases itself once a crust has formed, which takes roughly 2 minutes. Wait for it. Drying the fillet with kitchen paper first helps as well, because any surface water has to boil off before browning can start.

That is the usual way to cook it. The pan wants to be hotter than for anything else here, the sear is about 60 seconds a side, and the centre is meant to stay close to raw. Because it stays raw, the safety of it comes from the fish rather than the cooking: use sashimi grade tuna, or tuna that has been properly frozen, since freezing is what deals with parasites.

Not well. A frozen fillet sheds a lot of water as it thaws, which pulls the pan below browning temperature and steams the fish in its own liquid, and the outside overcooks while the middle catches up. Thaw it in the fridge overnight. If you have no time, bake it from frozen instead, because an oven copes with the extra water far better than a pan does.