A giant eyeball found washed up on a Florida beach is probably that of a giant swordfish, experts have said, bringing a disappointingly mundane ending to a bizarre marine mystery that set the internet abuzz with tales of monsters from the deep.

Since beachcomber Gino Covacci stumbled across the blue, grapefruit-sized body part as he walked on Pompano Beach, near Fort Lauderdale, on Wednesday, biologists from the Florida Fish and Wildlife Commission have been trying to identify the sea creature from which it was cut.

Suggestions included a giant squid, whose eyes can be as large as soccer balls, a bigeye thresher shark, which can reach can reach 16ft, a marlin or a particularly large sailfish.

The FWC has yet to release its official finding, but shark expert George Burgess of the Florida Museum of Natural History in Gainesville said he had spoken to one of the commission's scientists on Friday afternoon, who told him "eye in hand" that he was sure that it came from a impressively-sized swordfish.

"I'd say the fish was a pretty decent size, probably more than 10ft in length," Burgess said.

"There was a bit of bone left on the other side of the eye from where it was taken from the animal. That would eliminate a shark because they have cartilage, and on that basis it was likely one of the billfish."

Burgess said such a discovery was not uncommon along the beaches of south-eastern Florida, where a strong Gulf Stream often brings deeper-water creatures ashore – although he said the fish were usually intact.

In this case, he said, there was "clear human interaction", probably when fishermen aboard a boat dissected the dead fish and cut out the eye, intending to keep it as a souvenir.

"An eyeball like that is very impressive," he said. "I can see how it would freak people out. We keep the eyeball of a bigeye thresher in a jar in the laboratory here and people walking by it get spooked by this large, dead blue eye staring at them.

"Over the years we have had a number of interesting marine life washing up or caught in Florida," he added.

One of the most recent was in June last year, when a boatload of anglers came across a dead 23ft squid off Port Salerno on the state's Atlantic coast. It barely fit in their boat as they brought it back to dry land.

FWC spokeswoman Carli Segelson told The Guardian that marine biologists at the Florida Fish and Wildlife Research Institute in St Petersburg hoped to release their official findings later Friday or on Monday, after genetic testing.

"It's certainly generated a lot of calls," she said. "Everybody wants to know where this giant eyeball comes from."

Meanwhile, the eye's popularity continues to spread. A Canadian newspaper reported that a Facebook page featuring "the mystery eyeball" had received 1,000 likes and shares in less than 24 hours.