A huge, strange-looking fish washed up on a Southern California beach on Feb 19.

The 2.1m fish was later identified as a hoodwinker sunfish by researchers from California, Australia and New Zealand, said a post on Coal Oil Point Reserve's Facebook page.

The fish was found on a beach within the reserve and is the first record of this species observed in the northern hemisphere.

This species of fish is so rare that it was first discovered only in 2017.

An intern who discovered the fish first thought it was an ocean sunfish, which is known to be found in the channel near the reserve. She then posted the pictures onto the reserve's Facebook page.

An associate professor at UC Santa Barbara's ecology, evolution and marine biology department Thomas Turner hustled down to the beach when he saw the photos online. He then posted some images of his own onto an online scientist community website.

He told CNN: "It's the most unusual fish you've ever seen. It has no tail. All of its teeth are fused, so it doesn't have any teeth. It's just got this big round opening for a mouth."

Experts on the other side of the globe then weighed in to identify the fish.

Mr Ralph Foster, a fish scientist and the fish curator at the South Australian Museum, and Ms Marianne Nyegaard, the marine scientist who discovered the hoodwinker sunfish species, both felt that it was a hoodwinker sunfish rather than an ocean sunfish.

Where a fish normally has a tail, the hoodwinker has only a clavus - a structure that looks like a rudder, said Ms Nyegaard, who works in the marine division at the Auckland War Memorial Museum in New Zealand. All sunfish have a clavus but the hoodwinker's has a shape that's distinctive, she added.

She was very excited about the discovery.

"When the clear pictures came through, I thought there was no doubt. This is totally a hoodwinker," said Ms Nyegaard to CNN. "I couldn't believe it. I nearly fell out of my chair."

Samples of the fish were saved for future research, said the reserve.

In a reply to one of the comments on its Facebook page, the reserve explained more about the enthusiasm behind the discovery: "If the fish had died in open ocean, we would have never learned about its northern distribution, hundreds of parasites, age, size, DNA, etc."

Previous sightings of the hoodwinker sunfish were in Australia, New Zealand, South Africa and Chile.