Dunedin man Geoffrey Cole was at Steamer Basin on his lunch break and heard some regular anglers getting excited about a large figure in the water.
''They said 'Big shark, big shark'.''
He was able to identify the 1m-long rounded creature as a sunfish.
''It was amazing. I've seen some weird stuff down there in my time. You never know what's going to turn up next.''
Several onlookers followed the fish's movements throughout the day.
The museum usually recorded one or two sightings of the creatures per year, he said.
''They're common offshore, but you don't see them in the harbour that regularly.''
The fish were usually drawn into the harbour on flood tides, when currents from around Aramoana refilled the area after low tides.
They were known to get beached easily.
''It's good to know when that happens so we can confirm its identity and get some genetic samples.''
The sunfish was unable to be identified to species as Mr Fleury could not see it clearly enough yesterday
Sunfish mainly eat salp and other small plankton-based creatures.
