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“Most of the natural world is not discovered." Tiny parasitic jellyfish found in Watauga River fish

A brightfield microscope image of myxozoans, tiny jellyfish relatives. The myxozoans are teardrop shaped and have visible stinging cells inside them.
Steven Ksepka
Auburn University College of Agriculture
A microscope image of Myxobolus intralamina n. sp., a new species of parasitic jellyfish that infects the gills of smallmouth bass. Each of these tiny animals is about twice as long as a red blood cell.

Researchers have discoveredtwo new species of a bizarre, tiny parasite infecting smallmouth bass in the Watauga River.

The parasites, called myxozoans (Greek for “slime animal”), are related to jellyfish and sea anemones, but are much smaller, with only a few cells in the entire animal. They’re also much simpler – a previously discovered myxozoan speciesdoesn’t even have functional mitochondria, the only animal known not to need them.

Scientists found the two new species in fall 2020 during a routine survey of fish for parasites and disease, done by a partnership between the North Carolina Wildlife Resources Commission and a fish parasitology lab at Auburn University in Alabama.

Looking at every part of the fish under a microscope, researchers spotted one new species hiding out in the gills of the fish and one tucked under the scales. The two new species are each about as wide as a single human red blood cell, and twice as long.

New species appear harmless, unlike deadlier relatives

Jake Rash, the coldwater research coordinator with the North Carolina Wildlife Resources Commission, led the field efforts to collect the fish. The study was in large part motivated by the discovery of several non-native fish parasites in North Carolina waters, including a myxozoan that causes deadly “whirling disease,” Rash said.

These more dangerous myxozoans grow in the cartilage of young fish, Rash said, “ultimately causing swelling and compression on the spinal column. The fish that are heavily affected kind of tend to swim in a circle.” Whirling disease has decimated trout populations in other waterways.

The survey aimed to figure out what other parasites and diseases are hiding out in North Carolina ecosystems, so that if new diseases become an issue, scientists will know what to look out for. And thankfully, the newly discovered myxozoans don’t appear to harm their fish hosts, according to Rash.

Stephen A. (Ash) Bullard, a parasitologist at Auburn University who helped identify the new species in the laboratory, explains that doing this kind of survey work is an important first step to protecting ecosystems.

“There's a lot of undiscovered species out there. 99 percent of them are harmless,” Bullard said. “But it's important to document them so that you know what's harmful and what's not.”

Undiscovered species are probably everywhere

It’s not surprising that new species are still being discovered, according to Jerri Bartholomew, a professor of microbiology at Oregon State University who specializes in myxozoans.

“There are thousands of species of myxozoan and just about any fish is infected by one or more species,” she said. “Every time we go out and look at a new fish species or in a new location we're going to find more. I think what this really demonstrates is just the diversity and the number of them that have to be out there.”

Bartholomew estimates that there are probably more kinds of parasitic jellyfish than their freely swimming relatives, most of them still unknown. The new study shows that hidden biodiversity is everywhere.

“Most of the natural world is not discovered,” said Bullard. “We’re finding really interesting new species of new organisms that have never been named, never been described, even though they've been affecting fish for millions and millions of years.”

Sophia Friesen is a science writer and WUNC’s 2022 AAAS Mass Media Fellow. Before working with WUNC, they wrote for science news outlets including Massive Science, preLights, and the Berkeley Science Review, covering everything from wildfire mitigation to pterosaur flight abilities.
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