Symbolism, Imagery, Allegory
At the end of the novel, Peter abruptly decides to return to Russia to become a fisherman—but not the type you might think.
We know this because Nicholai is also a so-called "fisherman." But Nicholai doesn't actually do much fishing; instead he uses this profession as a cover to smuggle Russians out of the Soviet Union. So when Peter says that he wants to become a fisherman, what he really means is that he wants to go "'back to Moscow and get some more children and bring them to Nicholai'" (13.85). This makes sense to us, as it's pretty much what Peter has been doing this whole time: saving the lives of those in need.
Additionally, the idea of being a "fisherman" reminds us of this dude named Jesus, who's sometimes referred to as the "fisher of men" because he sought people out for Christianity, hoping to help by bringing them to new (religious) turf. In a similar way, both Peter and Nicholai are "fishers of men" (and ladies) themselves, dedicating their lives to helping the less fortunate make it to the promised land of democracy and sunshine. Not a bad gig, huh?