In Elizabeth Bishop's "The Fish," in lines 34-44, she uses several literary devices.
In writing of the fish's eyes, Bishop uses metaphors to describe them, comparing them to tinfoil, and again to isinglass.
...the irises backed and packed
with tarnished tinfoil
seen through the lenses
of old scratched isinglass.
Tin foil (also known as "aluminum foil"), as most people may know, is a metallic sheet, thin like paper that is most often used in cooking in the oven or on the grill. Because it is metallic in nature, it catches the light, reflecting it with some brilliance. Because the author notes that it is "tarnished," the reader gets the sense that it is a smoky-looking, the way foil looks having been used in a fire or left out in the elements ("environment").
"Isinglass" can refer to a transparent product made from fish bladders or to sheets of mica, which are most often smokily transparent, but also reflect light because of the flat surface that can mirror light as well. However, note that the author describes the surface as "scratched," so the reader knows it is not a clear reflection.
Sound devices (which appeal to the ear when the poem is read allowed, and often give the poem a musical sound) are used in the poem as well. Note the line...
... the irises backed and packed...
Assonance and consonance are used here. Assonance is the use of repeated vowel sounds (such as a, e, i, o, u) in a group of words. Consonance is the use of repeated consonant sounds (such as d, n, l, p, s, r, etc.).
In this phrase, the "a" sounds in "backed and packed" use assonance, creating a pattern of sound. Consonance can be found in these words as well:
...backed and packed...
Note the repetition of the "ck" sound in "backed" and "packed," as well as the repetition of the "d" sound in all three words.
We see alliteration in "tarnished tinfoil." Alliteration is the repetition of a similar sound at the beginning of a group of words, here found with the use of the "t" at the start of each word.
In all of these devices, assonance, consonance, and alliteration, the pattern is not found in using the same letters, but in employing the same sound. This is what makes them "sound devices!"
Bishop follows the motif of eyes in this section of the poem, but not of sight!
Vision is an important sensory system for most species of fish.
However, the use of "shallower" indicates a lack of sight, as does "tarnished tinfoil" and "scratched isinglass." This continues with...
They shifted a little, but not
to return my stare.
--It was more like the tipping
of an object toward the light.
There is the sense, beyond a lack of eyesight, to a lack of conscious thought, at least in "human" terms—for the fish does not "return my stare." Note the use of special punctuation, "--", before "It was more like..." This tells the reader to make special note of the difference between what eyes usually do ("stare" or look) as opposed something done by eyes that don't see well: catching the light, but not processing sight.
A simile is used in "more like the tipping / of an object toward the light." This compares shifting eyes to a "tipping...object."
Note another comparison at the beginning of the author's eyes and those of the fish:
I looked into his eyes
which were far larger than mine
but shallower, and yellowed...
Literary devices are forms of imagery for the purpose of painting a mental picture for the reader.