Its eerie blue hue was attracting plenty of curious onlookers who crowded around a glass jar yesterday -- but its sting could be deadly.
A poisonous Portuguese Man O' War has been found alive in Irish waters, sparking fears that larger swarms could follow.
The discovery, in a lobster pot off the Kerry coast at the weekend, could mean more of the fish are on their way here, a marine biologist warned yesterday.
Kevin Flannery, who specialises in exotic fish and is attached to Dingle's Oceanworld centre, said that although the Man O' War was attractive, it was potentially very dangerous.
The Man O' War -- so called because of its resemblance to 16th century Portuguese battle ship -- is not strictly a true jellyfish, but is closely related.
Its long poisonous tentacles, which can sometimes be up to 50 metres long, contain venom which would still be active even if the fish were washed up dead on the beach.
Lobster fisherman, Richard Sheehy hauled up the specimen in his pots on the Blasket Sound on Sunday.
He knew it was unusual and placed it in a bucket before handing it to Mr Flannery of Oceanworld.
"They are extremely dangerous," Mr Flannery said. Stings travelling through the human lymph system can lead to fever, shock, as well as heart and lung problems.
The Man O' War rarely swims alone, and we could be expecting swarms of the fish before long, he added.
Although the fish is native to warm waters, more exotic species have been appearing around Ireland in recent years.
The Man O' War fish inflates its bladder with air which allows it to "sail" like a ship in the wind.