Several years ago there was a viral video of a young whale jumping out of the water after it was freed from a tangle of fishing line. It put on a show for over an hour.
A friend of mine cut loose a fish that had been hooked and then just tied (with the hook in its mouth) to a piling. After she took the hook out of its mouth and let it go, it swam around in our area, jumping out of the water a couple of times, before swimming away. Not sure if it was grateful for being let go or if it was just testing to make sure it wasn't tied up any longer.