He saves others from danger, and serves the country-store owners; Edward performs assigned labors. He fights for the hand of his beloved Sandra.
And when William is with his father in the hospital at the end of the book, the almost-immortal Edward has nearly vanished, since the life support machines "had become him. They were telling me his story" (171)—although on the final page of the novel we learn that the sophisticated medical machines had less transformative power than Edward's stories.
William realizes that his father "was becoming a fish," but that simply meant "He was just changing, transforming himself into something new and different to carry his life forward in"—that is to say, he becomes the last of the stories of this man who became his own story.
The last sentence of the book is "No one believes a word" (180), and yet we have believed the story, in that manner that fiction can be truer than reality, fantasy more important than arithmetic, and a myth as big as a universe. Now we understand the last sentence of William's supposed preface: the father has become a child again, although he will grow up into a very big fish in the river now, generating stories that will surround his ongoing miracles "of lives saved and wishes granted" (180). That is to say, in that concluding sentence of the preface, "My father became a myth"…