Scientist's ode to daughter: Naming rare catfish species 'Sofia'

Mark (left) holding “Panaque armbrusteri,” Sofia (right) holding “Scobinancistrus pariolispos,” both popular species of plecos in the aquarium hobby. Courtesy Mark Sabaj Perez.

On any weekday evening after school has let out for the summer, you might find an 8-year-old girl in the back room of the Academy of Natural Sciences of Drexel University, slicing the eyes off a dead fish. She might take a specimen apart and diagram its spine on a piece of scrap paper, or study the fine, bony whiskers under a microscope set aside just for her.

This girl is Sofia Sabaj Pérez. As of this spring, the rising third grader has something most children don’t: a rare species of catfish named in her honor.

Sofia holding and imitating the Flatwhiskered catfish, “Pinirampus pirinampu.” Courtesy Mark Sabaj Pérez Perez.

Mark Sabaj Pérez, Sofia’s father, is the academy’s interim curator of ichthyology, the branch of zoology dealing with fish. Sabaj, a scientist with a casual air (his de facto uniform is jorts and a polo shirt that reads “Catfish Study Group 2013”), is trained in taxonomy –– the field concerned with identifying species, describing them, and giving them names. For years, Sabaj worked on the All Catfish Species Inventory, a project with a mission as impossibly simple as its name: to identify every species of catfish on the planet.

Since age 2, Sofia, an elfin ichthyophile with a mop of brown locks, has accompanied her father on research trips across the world, collecting catfish to bring back to Philly.

Sabaj recently christened a newly discovered catfish –– a species of the “banjo” family, so-called for their shape (round head, narrow tail) and the slender bones in their spines that  sound like a banjo when moved. The fish is especially small, measuring just over 44 millimeters from nose to tail. The academy has the only museum specimen in the world.

Sabaj called the discovery Xyliphius sofiae: Xyliphius for its genus of South American banjo catfish and sofiae for his youngest researcher: Sofia.

“Xyliphius sofiae,” the only museum specimen of its kind in the world, is completely eyeless and without pigment. Courtesy Mark Sabaj Pérez

Sofiae has a dual meaning,” Sabaj said. “One is for my daughter, of course. The other has to do with the Greek stem of the word –– soph –– meaning wisdom.” In the final paper, the etymology reads: “In honor of the daughter of first author on the specific epithet, for inspiring wisdom in her father.” Last week, Sofia printed out the official museum label and taped it to her bedroom wall.

Often, people dole out names before they know what they are naming. Sabaj decided on Sofia, for example, long before he discovered his daughter also enjoyed the company of sea creatures. The reverse is true with fish. In taxonomy, titles come last. Sabaj caught, studied, and described Xyliphius sofiae years before he knew what to call it.

In 2012, Sabaj had been collecting specimens along northern Brazil’s Xingu River, a tributary of the Amazon. Two years later, it became the site of the third-largest hydroelectric dam in the world. The All Catfish Species Inventory was under pressure to gather as many fish as possible before the dam permanently altered their habitat.

With the help of some local fishermen, Sabaj floated two canoes down a narrow river channel, dragging a fine mesh net between them. In one haul, he saw an inch of whiteness among the jumble of fish. The critter was thumb-knuckle length, eyeless, and without pigment — all rare traits within its genus of catfish. Sabaj Pérez realized instantly that it was new.

“It felt like finding a needle in a haystack,” Sabaj said. “The fish was so small and pale.”

Taxonomists can’t simply declare a new species. They have to assume they’re wrong. After the discovery, researchers must try to disprove themselves. Sabaj and his team combed museum collections, archives, and scientific inventories, looking for a pasty, blind catfish to prove X. sofiae wasn’t alone.

Verification is a long, arduous process that can occasionally take decades. In one extreme case, academy ichthyologist John Lundberg waited 39 years to name his catfish. He had collected the specimen, incidentally also eyeless and translucent (although of a different genus), in 1978. The anonymous fish finally became Micromyzon orinoco in February.

Mark Sabaj Pérez holding “Xyliphius sofiae” over his palm.

But by 2016, Sabaj and his colleagues had not found another catfish like theirs, and they were certain they would not. Sabaj even went back to the Amazon and tried to catch another. He could not turn up a second specimen, not because the fish are endangered, but because X. sofiae lives deep under the murky Amazonian waters, beyond the reach of his nets. Only after returning empty-handed did the team move forward with a name.

When Sabaj told Sofia about her namesake, she asked whether she was famous.

“Sure,” Sabaj said. “Among ichthyologists, you’re a celebrity.” For a girl who plays in rooms lined with jars of dead fish, that’s no small feat.

According to Sabaj, Sofia has always had a taxonomist sensibility.

“She has a knack for collecting things and sorting things, be it stuffed animals or Matchbox cars,” he said. “She has that classification bug.”

Classification, the science of putting things in order, is no easy bug to catch. It is an unrelenting enterprise –– there is always a new thing to name.

At the very least, the task outlasted the All Catfish Species Inventory’s formal undertaking. Funding for the project has long run out. Did they identify everything?

“No,” Sabaj said, laughing. Catfishes exist on every continent –– even as fossils in Antarctica. They inhabit every kind of waterway, including some running underground. But Sofia, Sabaj, and his colleagues are still collecting, dissecting, and describing specimens.

“But this one is done,” Sabaj said. “There’s a kind of relief in naming. I’m done with that. Now we can work on the next one.”