Where It All Goes Down
We're under the sea in "The Fish," but then we're above the water for a moment checking out a beat-up cliff that's also "defiant." And then we're in the sky—nope, make that back in the sea. So, although we're constantly moving from one setting to the next, the poem all takes place in pretty much the same vicinity, with related settings dissolving into one another. And when we consider ecosystems more generally, we understand that settings and creatures constantly rub elbows.
The "black jade waters" are hitting the "defiant edifice" that's on land, so nothing is ever that separate. People in the natural world work the same way. We may think we're on opposite sides of the globe, but there's always some sort of interaction to be had. At the same time, we're also inextricably linked to natural settings, no matter how urban our experience might be. The point is that this whole "man versus nature" thing is a lot less cut and dry when it comes to setting.
In this poem, the wavy movement of the lines helps make our transitions between settings run a bit more smoothly and keeps everything together under the sun. And since the poem looks like a fish that is itself on the move, the changes don't feel all that out of place. At the end of the day, we understand that, like those sea creatures, we all "slide each on the other" (25).
Chronologically, we get some subtle allusions to wartime here. When this poem was published, after World War I, life was as confusing as ever. There just weren't many simple answers to be had as to why all the violence, which occurred on a previously-unimaginable scale, was happening. So the references to cycles of life and death make a bit more sense in that context.