So long, and thanks for all the fish

So Long, and Thanks for All the Fish is the fourth book of the Hitchhiker's Guide to the Galaxy "trilogy" written by Douglas Adams. Its title is the message left by the dolphins when they departed Planet Earth just before it was demolished to make way for a hyperspace bypass, as described in The Hitchhiker's Guide to the Galaxy. A song of the same name was featured in the 2005 film adaptation of The Hitchhiker's Guide to the Galaxy.