When you are a child, go to the fishing pond and start fishing like normal. Keep fishing until you get a fish that's big enough to earn a heart piece. Instead of going to the fishing owner, go into the middle of the pond. Face towards the owner in the water and hold Z + R (lock and shield). Don't let go and swim and run to him. Once you reach him, talk to him without letting go of Z and R. He'll give you the golden scale instead of a heart piece!

This allows you to do many things early on. Such as entering Zora's Domain without having to play Zelda's Lullaby. Or getting the heart piece from the Lakeside Laboratory (letting you have both the scale and heart piece.)