When you visit the Dock Colony for the first time, a woman in front of the 
clinic tells you of a Fish Detector that her husband lost. Go to the Kukai 
Foundation's cleaning place and inspect the tuxedo to find the Fish Detector. 
Talk to the girl in the Iron Man bar, sitting at the lower left table. She 
says that she lost an important ring and asks you to find it. Go to the Private 
Beach and go in the water where the fish show up on the radar screen. Run up 
to every fish and press Circle. Sometimes you will get an item, and sometimes 
you will not. You can get a Med Kit, a Speed Stim, and the Engagement Ring. If 
you return to the beach on any return trips, the Med Kit, and Speed Stim will 
be there again. Give the ring back to the girl in the bar. She will give you 
the Decoder #8 to open the red door.