When people make hairtail, they often scrape the fish noodles like other fish, thinking that the fish they don't clean has a fishy smell. This idea has no scientific basis.
The silvery white substance on the body surface of hairtail is a kind of fat, which has no fishy smell. Removing it undoubtedly reduces the edible value, so you only need to wash the hairtail with water. The fishy smell comes from fish meat. The longer you put it, the greater the fishy smell.
The fish scale has industrial value. It is scraped off and put in the jar for fermentation and decay, and then wash away the spoils. The remaining silver white powder is dried to obtain the fish scale powder. It is a special silver white flashing dye and can be used in plastic products, so the fish scale powder is expensive.