New elusive sunfish species discovered

Scientists have discovered a new species of gigantic ocean sunfish - that could weigh up to two tonnes - after it remained hidden for three centuries. Iconic ocean sunfishes are the heaviest and most distinctive of all bony fishes, with some species weighing in excess of two tonnes and growing to three metres in length. The newly discovered species, named the Hoodwinker Sunfish, is thought to approach a similar size, researchers said.

Marianne Nyegaard from Murdoch University in Australia uncovered the new species while researching the population genetics of ocean sunfish in the Indo-pacific region. Nyegaard, began her investigations after noticing genetic differences in sunfish samples from the Australian and New Zealand long line fishery. "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 did not know what it looked like," Nyegaard said.

Researchers collected data from 27 specimens of the new species, travelling thousands of miles or relying on strangers to take samples of sunfish found stranded on remote beaches over a period of three years. "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," she said. The species is the first addition to the Mola genus in 130 years. The process we had to go through to confirm its new species status included consulting publications from as far back as the 1500s, some of which also included descriptions of mermen and fantastical sea monsters, researchers said.

"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," they said. Similar to its two sister species, Mola mola and Mola ramsayi, the new species has the characteristic truncated appearance of half a fish, but the differences between the three species become clear with growth, researchers said.

Mola tecta remains sleek and slender even in larger sizes, differing from the other species by not developing a protruding snout, or huge lumps and bumps. Researchers suspect that, as with other sunfish species, feeding takes place during deep dives. The digestive tract contents of three specimens they sampled consisted mostly of salps, a gelatinous sea creature loosely resembling a jellyfish.

Mola tecta appears to prefer cold water, and has so far been found around New Zealand, along the south-east coast of Australia, off South Africa and southern Chile, researchers said. The study was published in the Zoological Journal of the Linnean Society.