Dolphins, with their large brains, are seen as highly intelligent, sensitive creatures - English author Douglas Adams certainly saw the mammals that way.
This book's eponymous farewell slogan, addressed to humans on the dolphins' departure from earth before it is destroyed to make way for a hyperspace bypass, captures something of how our sea-faring friends outsmart the human race.
So Long, and Thanks for All the Fish (the fourth in Adams' The Hitchhiker's Guide to the Galaxy "trilogy" - and there was even a fifth), follows the story of Arthur Dent, who hitchhiked through the galaxy and back to earth, much to his confusion since he had seen the planet destroyed by aliens.
Back home, Arthur learns that all the dolphins have disappeared from earth. He finds a gift-wrapped crystal bowl engraved with the words "So long and thanks …" and decides to keep his Babel fish (a universal translator inserted into the ear) in it. He travels to California to visit a man named Wonko the Sane who also has a crystal bowl, but his is engraved with the whole message: "So long and thanks for all the fish."
The comic irony is foreshadowed neatly by Adams, who has Arthur coming home to an old Greenpeace letter seeking help in releasing dolphins and whales from captivity. And perhaps there is some darker irony here, too, with the dolphins' departure a sarcastic thank you to humans for feeding them fish while they were kept in captivity as performing animals.
Seeking to make sense of their dolphinless world and the wider galaxy, Arthur travels through space to a planet in order to read "God's Final Message to His Creation": "We apologise for the inconvenience"; and this is pretty much where the book ends.
Adams delivers his messages in a light, humorous tone that mocks and scorns humanity. As Wonko puts it, while explaining his retreat from the world: "Any civilisation [that needed] to include a set of detailed instructions for use in a package of toothpicks was no longer a civilisation in which I could live and stay sane."
The author's quips, quirks and playful, sarcastic tone lent itself to spoofing - So Long, and Thanks for All the Fish has been adopted by sci-fi fans as the long form for "goodbye"; rock band NOFX titled one of their albums So Long, and Thanks for All the Shoes; and All Time Low had a track called So Long, and Thanks for All the Booze.