The 1.8 metre specimen — believed to be a Mola mola, or ocean sunfish — came ashore near the mouth of the Murray River in South Australia and was discovered on the weekend.
A photo of the creature was posted on social media on Monday, with two fishermen standing over it on the sand.
Linette Grzelak, who posted the image to Facebook, said her partner spotted the unique beast (which was already dead) while out fishing.
“A sunfish found by my partner along the Coorong a couple nights ago … I thought it was fake,” the post said.
The enormous creature is distinct for both its large size and peculiar qualities, featuring a flattened body and fins. The fish can weigh up to 2.5 tonnes, or 2200 kilograms, according to National Geographic.
“These huge beauties are the world’s largest bony fish and can weigh more than a car,” National Parks South Australia said on Facebook alongside the pics.
Due to the rarity and stunning nature of the animal, the story has made headlines around the world, appearing on the BBC, CNN and USA Today, among many others places.
“The amount of news and media from all over the world wanting to report it has been on another level,” Ms Grzelak told the Paris-based wire service AFP.
“Never expected this.”
The discovery of the fish even prompted a piece in The Atlantic about all the wonderful oddities of the “fundamentally bizarre” animal.
“Ocean sunfish are huge, weird, surprisingly graceful — and still mostly a mystery to scientists,” the article said.
But there are some things we do know about the large sea creature. They have weird teeth in their throat, they appear to play dead on the ocean surface while soaking up some rays, and they have been recorded swimming as fast as 6.6 metres a second, although researchers are a little baffled how they achieve this. When they have warmed up in the sun, the fish will dive hundreds of metres below the surface and feed on things like jellyfish.
The Mola mola also has a reputation for damaging boats. There have even been instances where the animal has been blamed for sinking yachts.
A yacht that competed in the Sydney to Hobart race this year went down off Flinders Island in January after it hit a sunfish “as big as two 44-gallon drums”, The Mercury reported. The yacht lost its rudder in the impact with the fish and started taking on water while returning to the mainland after competing in the race.
Instances like this are perhaps why the fish has attracted some less flattering descriptions, such as being dubbed a mistake by Mother Nature and the most useless fish in the sea by its more harsh detractors.
Speaking to the ABC this week, South Australian Museum fish collection manager Ralph Foster said the fish that washed up in South Australia was actually at the smaller end of the scale for the species.
“I’ve actually had a good look at it, we get three species here, and this is actually the rarest one in South Australian waters,” he said.
“They can get a lot bigger … it’s probably an average-sized one. They can get nearly twice as big as that.”
It’s only been in the last few years that technology had allowed us to learn more about the mysterious Mola mola, Mr Foster said.
“They are amazing things, they really are,” he said.