Of all things,leak colleagues sex video Marianne Nyegaard didn't expect to find a new species of sunfish -- the heaviest of all bony fishes.

The PhD student from Murdoch University in Western Australia made the discovery while researching the population genetics of ocean sunfish off the coast of Bali in Indonesia.

Previously undescribed, it's called the Hoodwinker Sunfish (Mola tecta). The fish has long eluded recognition from researchers, despite the species weighing in excess of two tonnes, and growing to three metres in length.

"A Japanese research group first found genetic evidence of an unknown sunfish species in Australian waters 10 years ago, but the fish kept eluding the scientific community because we didn't know what it looked like," Ms Nyegaard said in a statement.

Nyegaard spent four years searching for the fish, after genetic sequencing of 150 specimens in her research turned up with four different species: Masturus lanceolatus, Mola mola, Mola ramsayi, and a fourth which wasn't known about, she explained in her article on The Conversation.

So in her quest to find the missing species, she'd travel thousand of miles to get data, or have kind strangers send samples of sunfish stranded on beaches.

In 2014, Nyegaard was a step closer, when she was sent a photo of a tiny sunfish, with a structure on its back she had never seen before. Then a breakthrough came.

Nyegaard was tipped off to four sunfish stranded on the same beach in New Zealand. She flew down to see it herself, where she spotted her first Hoodwinker Sunfish.

"The new species managed to evade discovery for nearly three centuries by ‘hiding’ in a messy history of sunfish taxonomy, partially because they are so difficult to preserve and study, even for natural history museums," Nyegaard said.

"That is why we named it Mola tecta(the Hoodwinker Sunfish), derived from the Latin tectus, meaning disguised or hidden."

The Hoodwinker Sunfish is the first addition to the Mola genus in 130 years, and differs from other sunfish in that it remains sleek and slender even when large, and it doesn't develop a protruding snout, or huge lumps and bumps.

"We retraced the steps of early naturalists and taxonomists to understand how such a large fish could have evaded discovery all this time. Overall we felt science had been repeatedly tricked by this cheeky species, which is why we named it the Hoodwinker," she explained.