Marmite lures discovery from lake depths

Dr. Roe Stuart didn’t find a taniwha in the unexplored depths of New Zealand’s lakes—but they may have found a new species of fish.

“We have four lakes in New Zealand that exceed 400m (1,300 feet) deep, and the deepest records we had of fish life were 90m (300 feet),” says Stuart, who realized while doing postdoctoral work at Lake Champlain in the U.S. that no one knew what lurked in Aotearoa’s lakes.

“I just wondered what would be down there.”

A depth sounder found Lake Manapōuri and Lake Te Anau to be 467m (1,532 feet) and 430m (1,411 feet) deep, respectively—about the height of Dunedin’s Saddle Hill.

Searching for signs of aquatic life in the unexplored waters required 2km (1.2 miles) of rope, multiple traps set at different depths and … a breakfast spread?

“We baited the traps with Marmite,” Stuart says. “I’ve had quite a few people ask if Vegemite also works, but why risk it?”

When the team returned the next day, they pulled up the traps that had been set at different depths—and found fish in all of them.

“There’s fish in here!” Stuart exclaims, reliving the moment of discovery. “It’s not very often that you get to have that ‘we’re the only people that know this’ moment.”

Stuart found native bullies and galaxiids—small (about 12cm [4.7 inches]), iridescent climbing fish that are sometimes caught as whitebait.

“We suspect the galaxiids are kōaro or kōaro-adjacent,” Stuart says.

“They’re very different from our standard assumption of what a kōaro is, so they’re either an adaptation or a new species.”

The fish have characteristics that are atypical for kōaro.

“Their eyes are huge compared to regular kōaro, and the other really cool thing about them is that they have these amazingly large sensory pores on the top of their heads. There’s no light down at the bottom of the lakes, and the sensory pores likely help them navigate their habitat.”

Genetic testing will determine whether the fish are indeed a new species, but Stuart is thrilled to have found life in the lake depths at all.

“No one’s worked in New Zealand’s deep lakes before, and everyone I talked to was somewhat skeptical I might find anything—so the fact we found fish in both lakes was hugely exciting. It’s hard to protect and care about something if you don’t know it exists.”

The discovery provides new information and raises fresh questions.

“The fact the lakes have oxygen all the way down is informative in itself,” Stuart says.

“It brings in questions about the human impacts on the surface. We don’t necessarily think about those really deep basins, so how our impacts transfer is something we should consider for future management of these iconic, deep-water lakes.”

Finding hidden fish is a change of pace for Stuart, who’s used to chasing aquatic life around the lab.

“I did a postdoc at the University of Vermont, looking at American eels. They wanted to see if the eels were eating sea lamprey, an invasive species in the inland waters that had gotten in through canals and were really detrimental.”

As part of the experiments, Stuart and the team kept eels and crayfish in their labs.

“Eels are escape artists. I lost one that went down the drain and turned 90 degrees before getting stuck at a T-junction,” Stuart says.

“I got it out, but it turns out crayfish are as hard to contain as eels. We had crayfish roaming around the lab. After that, all our tanks had lids and tape so they wouldn’t get out.”

With Stuart’s arms adorned with tattoos depicting eels, zooplankton and torrent fish, it’s clear they’re passionate about the inconspicuous creatures that inhabit our rivers and lakes.

“Fish are surprisingly charismatic. They’re fascinating, they have such complex behaviors, there’s so much diversity of fish, and there’s still so much we don’t know. Someone needs to speak up for them,” Stuart says.

“Something calls to me about the overlooked and underappreciated.”

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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