A huge theme of Bless Me, Ultima is understanding and questioning the dogma of organized faith. Antonio is already beginning to doubt the teachings of Catholicism when he first discovers the golden carp. Supposedly, its purpose is to guide the rest of the carp, who are the souls of sinners in a previous life. Antonio feels astounded that the carp is actually tangible and visible, and he gets a sense of enlightenment and religious fulfillment that he has never felt from Christianity.
The golden carp serves as an iconic symbol for Antonio's religious transformation. He even tries to show it to his agnostic friend, Florence, so that the latter might believe in something. However, Florence drowns before he can see the carp. This, combined with the carp's meaning to drown sinners, sets Antonio on a path of doubt once again.