What do Cico and Tony agree to do?

Antonio is fishing and wondering why Ultima was able to cure Lucas when the priest could not. He hears someone calling him and discovers Cico, the boy who Samuel had promised would take him to see the golden carp. Cico offers to show Antonio the golden carp, and Antonio enthusiastically agrees. His only concern is that he is Christian, and he does not know if he is allowed to believe that the golden carp is a god as Cico does. Cico makes Antonio swear an oath that he will never kill a carp and then leads him off into the direction of the carp.