Fish (motif)
Images from the Aquarium in the first stanza resurface throughout the poem, but their echoes are sometimes contradictory. Lowell calls the fish "cowed, compliant" and compares them to the huge cars in the modern-day street; these cars are menacing in a way the fish are not.
He always implies a parallel between the fish and black school-children he sees during coverage of the Civil Rights Movement on TV. Both of them he sees behind a screen or glass, and he sees bubbles rising from both of them. With the words "cowed" and "compliant" attached to the fish, this seems like a questionable choice.
Bubbles/balloons (motif)
In the second stanza, Lowell as a child longs to pop the bubbles in the Aquarium, but he is prevented from doing so by the glass. A moment later in the poem echoes this one: "the drained faces of Negro school-children rise like balloons." He is unable to pop them through the screen. Lastly, Colonel Shaw "is riding on his bubble" and waiting "for the blessèd break." Do the bubbles indicate distance between the narrator and these subjects because he cannot reach them? Are the bubbles a straightforward symbol for prejudice? If so, does that indicate that they have a natural breaking point?
Statues and monuments (motif)
The narrator considers what it would mean for all the monuments in New England to disappear, and how the world where that could happen would look. The central monument is the bronze relief of Colonel Shaw and his soldiers, but Lowell thinks of all the memorial statues in New England. He does not want to erase history and thinks that it would be detrimental to society to do so, but these statues, like the Aquarium, could one day disappear.
The ad for Mosler Safes is presented as a shoddy modern parallel to these monuments, memorializing war crassly for monetary gain. Monuments, on the other hand, are inviolable, but lose significance as people stop paying attention to them.
