I've watched it again today. I don't normally watch movies twice in the cinema, but this is so good I couldn't resist. I loved it.
I felt that where Edward turns into a fish when when he dies relates to an earlier part in the movie when he was leaving Ashton and the witch told him "the biggest fish in the river gets that way because he was never caught". Then the closing line where William was saying that the "man has become the story" makes me think that Edward has indeed, 'became' his story, and continues to live on although he has passed. In that way, he has become the "biggest fish in the river"