Translation:Do you have fresh fish?
Why is "Do you have fresh fish?" incorrect nobody says "do you've"
It's not incorrect, it's the preferred answer.
Any reason why "are you having fresh fish" is not a correct answer here?
Are you having fresh fish, indicates that you are eating it. That is not the meaning of the Dutch sentence.
What is the difference between vres and verse?
https://www.duolingo.com/skill/dn/Adjective-Basics/tips-and-notes