What is the symbolism of fish in the novel, Dinner at the Center of the Earth?

In Englander’s novel, the fish represents the human without agency. In Berlin in 2002, Farid and “Joshua” discuss the way to be successful. Farid claims, “You need fish to catch fish” (76). This statement implies the gullibility of people. Humans are fooled by false appearances, the same as fish are fooled by bait. Twelve years later, “Joshua,” now Prisoner Z, metaphorically calls himself a fish. He tells the guard: “Come in so I can show you from where the fish pees!” (153). Prisoner Z threatens the guard, but in the same sentence, implies his own lowly status by referring himself as a fish.