I like to fry fillets or whole fish using the following breading recipe. I fry in peanut oil and seek to maintain it at 360 degrees in my fish cooker. I cook them until they are brown and floating. What has been said about the thermometer is correct, have a good one and keep it in the oil.

Breading recipe
6 cups of self-rising flour
1 cup self-rising white cornmeal
1 Teaspoon of salt
1 Teaspoon of pepper

And don't over crowd your pan/pot that way the fish fry quicker and better. And, add some friends to the menu that way the fish always taste better!