Answer:
Long and slinky like a trout, never sings till it's guts come out.
What has roots that nobody sees, and is taller than trees. Up, up it goes, and yet it never grows.
Has no feet, but travels far. Is literate, but not a scholar. Has no mouth, yet clearly speaks.
What goes around and around the wood, but never goes into the wood?
What is pronounced like one letter, written with three letters. And belongs to all animals?
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.