Symbolically connect Waverly to the fish the family eats for dinner in the final scene.
“On a platter were the remains of a large fish, its fleshy head still connected to bones swimming upstream in vain escape.”
Waverly, the narrator and young chess champion who keeps struggling with her mother, describes the family’s dinner this way. She’s just shown up at home after being out by herself for a few hours, having run away from her mother in the market. Waverly is very frustrated and embarrassed by the way her mother introduces her to strangers in the market; the girl seems to think her mother is taking credit for Waverly’s success as a chess prodigy.
But while Waverly is sitting alone, angry and cold and tired from running, she realizes that she has nowhere to go. There isn’t any escape from her mother or from her situation. This realization leads Waverly reluctantly back home to sit down to dinner with the family.
So, you can understand why Waverly would describe the fish on the dinner platter as a creature “swimming upstream in vain escape.” She identifies symbolically with the fish; both the creature and the young girl are trying desperately to find freedom and escape from the forces that are directing their lives.
With “its fleshy head still connected to bones,” the fish can also be symbolic of Waverly’s family unit. Waverly is the head; her mother is the bones. (Or vice versa, depending on your interpretation—I see Waverly as the head, since she’s the one facing a certain direction, trying to nudge away from her mother.) The mother and child, like the head and the bones, are connected to each other deeply. No matter how Waverly struggles to separate herself from her mother, she’s still a child under her mother’s care, and she’s still strongly influenced by her mother’s ideas and perspectives.