Thoreau admits that, lately, he's wondered whether fishing is somehow inhumane. He's already given up hunting and eating meat, since he believes animals suffer and feel pain.
He goes on to wonder whether it isn't the meat-eating part, so much as the way we eat that is the issue. Thoreau believes that people should only eat to sustain their animal existence. Savoring the deliciousness of food is just a distraction from higher intellectual pursuits. This guy wouldn't have lasted a day in Italy, that's for sure.
The chapter ends with a scene featuring a hypothetical man named John Farmer, whose only way to a higher spiritual state is to basically watch what he eats, which Thoreau implies is at least the first step toward self-respect.