Why is catching and eating a carp bad luck?

As they fish, Samuel tells Antonio the story of the golden carp. Many years ago, a people had lived in the land and enjoyed much prosperity. The only thing that the gods had forbidden for them to eat was the carp in the river. After forty years of drought, all of the plants in the land had died, and the people were forced to catch and eat the carp in the river to survive. The gods were so angry that they turned all of the people into carp and doomed them to live in the river for the rest of eternity. One of the gods took pity on his people and asked to be turned in a carp so that he could protect them. Antonio asks if the golden carp is still in the river, and Samuel tells him that, once the summer begins, his friend Cico will find Antonio and show him the golden carp to see for himself.