You can use the following methods to clean up the mucus on the surface of the three scales:

1. Use a knife to scrape off the excess mucus on the surface of the fish body, and then rinse it clean.

2. Sprinkle salt evenly on the surface of the fish body, then rub it vigorously, then sprinkle a small amount of flour or starch, continue to rub it for about 1-2 minutes, rinse it clean to remove the mucus.

3. Boil a pot of water, let it cool to about 80 degrees, slowly pour it on the surface of the fish body with a spoon, continue to scrape with a knife, and rinse it clean to remove the mucus.

After the above steps are completed, the mucus on the surface of the three scales can be completely removed.