stone ... fish ... snake

These nouns should be translated literally.

Or if he asks for a fish, will give him a snake?

Jesus asks another question to teach the people. It is understood that Jesus is still referring to a man and his son. AT: "And there is not one person among you, if his son asks for a fish, will give him a snake." (See: rc://en/ta/man/translate/figs-rquestion and rc://en/ta/man/translate/figs-ellipsis)