Get the Barheim Key, then go to the Dalmasca Eastersand Gate Crystal section and talk to Ruxera, who is looking at the river wanting to fish. Next, go to the south-east section of Port of Balfonheim, which is the road to Airship Terminal. Find the old fishing man around the crates area and talk to him twice, then choose the first option. Move away from the old man, but do not leave this area yet. After a bit, go back to the same place and the old man will be gone. Examine the fishing rod there to get Muramata. Go back to Dalmasca Eastersand and give the Muramata to Ruxera to start the fishing mini-game.