What are the motifs in The Fish by Marianne Moore?

Order versus disorder is a recurring idea. "The Fish" symbolically illustrates humanity's desire to impose order on experience and to make meaning out of a world in flux. The very opening of the poem attests to the elusiveness of meaning as the fish "wade / through black jade." Jade is a dark stone and, used here, underscores the absence of visibility in the sea. It is so difficult to see, in fact, that the fish can become lost, figuratively, and Moore focuses instead on the mussels. The shifting subject of the poem—from fish to mussel, to light, to cliff—underscores the axiom attributed to Heraclitus, that you can never step in the same river twice.