Settlers Cities and Knights + Fish: Cost of a commodity

Question

When using fish, the card states that 4 fish are used to buy a resource. What is the cost, in fish, of a commodity?

Answer 1

You cannot buy commodities using fish.

http://download.catan.com/en/download/?combination-Fishermen_Cities-and-Knights.pdf

• If you discard 3 fish, you may draw one card from the hand of one of your opponents (Resource or Commodity Card).
• If you discard 4 fish, you may take resource card but not a commodity.
• The following applies also for the combination with Cities & Knights: Fish are no resources – and no commodities. This implies that fish are never affected by Progress Cards, particularly not by the yellow Progress Cards.