Depends on what country you're living in. You'd have to check if you need to.
Where I'm from when you're into bitcoin you have to report that you are and how much you've made, depending on how much profit you got, you'd have to pay taxes over that.
There's no such thing as needing to declare it! How would they prove you got an digital asset? The only case you would need to do it is if you convert it to fiat...