According to critic Lloyd Schwarty Bishop is frimly in the ut pictura poesis tradition. That is, the use of Nature is like art, as in a painting or in a poem; nature, like art speaks to the viewer or reader. Elizabeth Bishop wants the readers of her poem "The Fish" to read the world around them.
Thus, in Bishop's poem, the speaker, who at first is merely fishing and catches the "battered and venerable" large fish, examines this creature of nature, noticing the various patterns and colors he possesses, much like a work of art:
Here and there
his brown skin hung in strips
like ancient wallpaper....He was speckled with barnacles,
fine rosettes of lime,
with tiny white sea-lice,
and underneath two or three
rags of green weed hung down.
And, as the speaker examines the "tremendous fish," she is filled with sympathy and awe at the majesty and bravado of the creature who has overcome several attempts at capturing him as she looks at the five pieces of wire and line "Like medals with their ribbons." Furthermore, as she "stared and stared," everything becomes "rainbow, rainbow, rainbow!" and she releases the fish to the lake. This rainbow represents the victory of not only the fish, but of the speaker, as well. For, she has read the world of nature and learned to appreciate its beauty and sympathize with it. Clearly, Elizabeth Bishop's poem is verse that is truly beautiful, deeply sympathetic to nature.
I think that the appreciation of the natural element can be a theme in Bishop's poem. I think that the idea of "And I let it go" helps to convey an understanding of how human beings must work within the natural setting and not work against it. The ending of the poem, in contrast to its start, helps to bring about the idea that individuals are a part of the this natural world and not poised against it. The act of catching the fish and them growing to understand its position in the world and the human being's relationship to it helps to enhance the idea that one of the poem's themes is a natural appreciation. In a larger sense, the poem helps to both value in the individual and devalue the individual in a grand configuration. Bishop's poem simultaneously praises in the human being, but also examines the human being's endeavors as small in the larger scope of consciousness. In this, the natural appreciation of the world can be considered a theme that arises out of the poem.