Fish maw — the swim bladder of a fish — is one of the most expensive dried-seafood products in the world. A Chinese delicacy, it can fetch $450 to $1,000 per kilogram.

Heat olive oil in a large stainless-steel skillet over medium-high until hot but not smoking; reduce heat to medium. Add fillets to pan, and cook, flipping once, until fish is golden brown on both ...