But that doesn't have any effect on the end result: the shark rips  it's dinner in half, killing it. Humans chop off the head of a fish, killing it. There is no difference in result, only in method, and the only ones who feel better for it are humans, who can pretend that because it wasn't 'too painful' it's perfectly fine to have killed that fish. There is no difference for the fish, which dies either way.