On first reading this book, you might assume that someone—one of the book's editors or maybe Seuss himself—got mighty lazy and decided to go ahead and name the book by its first four lines. Snooze.
Though this is a possibility, it's more likely that the title of the book represents the spirit and meaning of the overall story within, so we're gonna go right ahead and dig deeper.
One Fish Two Fish Red Fish Blue Fish certainly isn't your typical linear story. You know what we're talking about—"Boy meets girl. Girl and boy fall in love. They struggle and persevere. Fin." It's not even the typical story of, "Boy and girl meet fish. Fish are interesting. They take them home. Fin."
Instead, it reads like a raucous collection of mini-poems, a romp through an entirely Seussian animal kingdom, with a little bonus subplot involving Ned and his bed. Perhaps this is why the title can't fit into one or two words. It needs four whole lines of verse to get its widely ranging point across. This is a book about diversity, and the title is, too.
See, the first four lines of the book set up an expectation of differences among creatures. There are one fish, two fish, red fish, and blue fish. None of the fish are the same, nor should they be. As far as promoting the message of embracing differences goes, there's no better place to start than in the title of the book.
Finally, the title has all the fun of the rest of the book when it comes to short little rhymes that taste great rolling off the tongue. If there were an award for rhyming the same word over and over again, it would go to Dr. Seuss, though Kanye might get an honorable mention, too. By showcasing the rhyming spirit of the book and exposing the reader to a variety of characters before page one, the title neatly sets the reader up for what is to come.