Why does he say "Treasure is ticklish work"?

By "ticklish", the captain means dangerous.

“Next,” said the captain, “I learn we are going after treasure—hear it from my own hands, mind you. Now, treasure is ticklish work; I don't like treasure voyages on any account, and I don't like them, above all, when they are secret and when (begging your pardon, Mr. Trelawney) the secret has been told to the parrot.”