The Fish by Elizabeth Bishop; Who Caught The Fish?

In class last week, the general understanding was that Bishop is writing a poem about a fishing experience she had.
Yet, the contributing writers on the Bedford-St. Martin’s Virtualit site (Quentin Miller and Margaret Wald respectively) seem to take a very different approach. They refer to the fisher who's experience is recounted as a fictional second party. i.e. "the speaker" in the poem. As the first sample essay begins: "Elizabeth Bishop’s “The Fish” is a seemingly simple poem about a speaker who catches a fish, scrutinizes it, and lets it go."

http://bcs.bedfordstmartins.com/virtualit/poetry/fish_elements/fish_essay.pdf

http://bcs.bedfordstmartins.com/virtualit/poetry/critical_define/psychoessay.pdf

So is this poem based on fact or fiction? Did she catch a fish that looked as described (at least the literal parts of the description) who's usual appearance and hooks in his mouth inspired the symbolisms and the moral struggle described in the poem? Or did she create a story of a fictional fisher only to inspire them?