Thanks for the find. That 300 Golden Fish exchange was from a 2010 MapleSEA-only fishing event; it was never part of the version we follow, and the Golden Fish item doesn't exist here, so Kedrick doesn't offer it. Fishing stays as it is for now.

Update: the owner decided to add it after all! Kedrick at the Floating Market's west pier now trades 300 Golden Fish for a Strawberry Icecream Bar, and Golden Fish are the most common thing you'll reel in while fishing with Kedrick's bait. Live now.