In her single-stanza poem, "The Fish," Elizabeth Bishop uses the speaker's increasing attention to the details of a fish to shift the speaker's perception of  and feelings about the fish. It's a lesson in how attention to details can grant subjectivity to a seemingly lifeless object -- in this case, a fish.

The speaker's relationship to the fish changes at two key points. First the speaker observes that "He didn't fight," and that in fact, "He hadn't fought at all." This observation sparks a curiosity for the speaker, who then continues to note the fish's bloody gill, and the barnacles which had lodged on the fish's skin along with seaweed. The speaker then begins to personify the fish through noting the bone structure and physique until he/she gets to the jaw where "hung five old pieces of fish-line...with all their five big hooks/grown firmly in its mouth." This is the second and more startling realization. The speaker realizes that the fishing lines were "like medals with their ribbons." This is in stark contrast to the description of the fish as not fighting.

It is at this point where the speaker feels as though he/she and the fish are equal matches. We hear the speaker wax about how "victory filled up/that little, rented boat," both the past victories of the fish and the now realized victory of the fisherman who had managed to capture a worthy adversary. This realization fills the speaker with respect for the fish, and promptly sets the fish free, allowing it remain worthy of its own subjectivity.

The poet's attitude is an attitude of aloofness at first.  The poem starts off with a simple declaration.  "I caught a tremendous fish."  The sentence falls very flat though.  There is no exclamation point.  There is no feeling of triumph.  There is no vast description of the work that it took to catch the fish.  In fact, the narrator says that it didn't take any work to catch the fish.

"He didn’t fight.
He hadn’t fought at all."

The middle third of the poem is a description of how gnarled and grisly the fish looks.  It's brown, has algae growing on it, and has barnacles even.  It's not a pretty fish.  If anything, the tone mingles between aloofness and slight revulsion.  I mean at one point the narrator even describes the white sea lice that the fish has.  Gross. 

The narrator's attitude begins to shift with this line:

"I admired his sullen face"

The word "admired" signals the shift in attitude.  An aloof attitude doesn't admire anything.  But with that one word, the narrator signals the reader of his/her attitude shift.  It continues from there as the narrator describes how tough the fish must be to have survived five fish hooks in its jaw.  

Like medals with their ribbons
frayed and wavering,
a five-haired beard of wisdom
trailing from his aching jaw.

The shift in attitude is so profound that the narrator decides to let the fish go.