Answer:
Goes over all the hills and hollows, Bites hard, but never swallows.
I am a tool for fairies.
I dig out tiny caves and store gold and silver in them. I also build bridges of silver and make crowns of gold. Sooner or later everybody needs my help yet many people are afraid to let me help them.
I am sometimes referred to as chips
I go up and down at the same time. Up towards to sky and down towards the ground
Often cooked as fillet, this meat comes from an animal that swims underwater.