Technique: Scaling Fish
Scaling is a technique to remove scales from fish using a knife or fish scaler in a sweeping action going against the grain of the scales. Since the scales will pop out and even fly a great distance, this is often done holding the fish under running water to reduce the mess. Some people also scale fish inside a large clear plastic garbage bag to contain the flying scales.
Unless you caught the fish yourself and have no other choice, it is usually best to ask your fishmonger to do the scaling for you. They are much better equipped to do so than the average home kitchen. The area of the shop where they do the scaling is usually completely hosed down daily, if not even more frequently than that.