In "The Fish" what clues suggest that the fish might have a symbolic meaning and what could the rainbow at the end symbolize? "The Fish" by Elizabeth...

Elizabeth
Bishop's poem "The Fish" seems at first the telling of a "big catch," but as
the poem progresses the reader discerns that the speaker has a growing respect for this big fish
that is "venerable."  The speaker says that she "admire[s] his sullen face"
and the "mechanism of his jaw."  Upon closer inspection, the speaker of the poem
notices five pieces of old fish line with hooks that have "grown firmly in his
mouth.

These hooks and lines are

Like
medals with their ribbons

frayed and wavering,

a
five-haired beard of wisdom

trailing from his aching jaw.

At this point the speaker senses that "victory" fills up
the boat as she recognizes the five times that the old fish has defeated other fishermen.  Like
ribbons won for this victory, a rainbow caused from the mixing of oil in the bilge of the boat
spreads its colors.  When the speaker says "everything was rainbow, rainbow, rainbow!"
she feels that the old winner deserves to be let go.  Thus, the rainbow reminds the speaker
of winning awards, and, in her release of the old fish, the rainbow comes to symbolize the
renewal of life as it does in nature.

Critics Lloyd Scwartz and Sybil P.
Estes write,

Bishop's poetry is pictorial not only in the
sense of giving vivid description of natural phenomena, but also in it use of artificial object
to relect on the self-referential aspect of art.  Nature is like art...nature speaks.

Nature, the old walleyed pike, and art, the creation of a rainbow
in the bottom of the boat, speaks to the person holding the fish and he/she understands the
venerableness of this fish; out of respect for its having defeated five others who have caught
it, the fish is released.