Small whole fish, steaks, and fillets may be sautéed. When the skin of the fish is heavy and tough, it is removed before the fish is sautéed.
Flat fish (sole, turbot, flounder) and skin fish (catfish, large-mouth black bass, etc.) have tough skin. They are skinned.
Round-type fish (trout, perch) usually have tender skin. They are scaled and not skinned before they are sautéed. Of course, there are always exceptions.
Before cooking whole fish with the skin on, be sure to slash the skin in several places to allow for contraction as the fish cooks. Failure to do this may cause the fish to crack or its shape to be distorted as it cooks. Also slash the skin that surrounds fish steaks so they will remain flat and not buckle.