The skinny on the search for the Fat Catfish

More than 9,000 feet (3,000 meters) above sea level, in the Eastern Cordillera of the Andes, a search is underway to find a lost species of freshwater fish in Colombia’s largest lake.

Last seen in the wild in 1957, the Fat Catfish (Rhizosomichthys totae), or “Pez Graso,” is endemic to Lake Tota and possibly its surrounding bodies of water and tributaries. (More research is needed to determine if its range includes bodies of water and tributaries around Lake Tota). The International Union for the Conservation of Nature (IUCN) lists the species as Critically Endangered and a multidisciplinary team of researchers is hoping to find the fish or at least evidence of it, as part of the Search for Lost Species.
 
Carlos Andrés Lasso Alcalà, an ichthyologist who works at the Instituto de Investigación de Recursos Biológicos at Alexander von Humboldt Institute in Bogotá and Susana Caballero, an associate professor at Universidad de los Andes, who specializes in conservation genetics, are co-leading current research trips to Lake Tota.

“It’s a bizarre species,” Lasso said. “The Pez Graso has a special anatomy and morphology, with rings of probably oil or ‘grasa,’ but we don’t have any information about the size, the biology, the feeding habits, or the growth of this species. This lake is very interesting because it has a lot of invertebrate diversity:  crustaceans, freshwater sponge, zooplankton, phytoplankton, and a lot of other aquatic animals.”
 
The ecosystem of Lake Tota is unique in a country that ranks among the top three countries for biodiversity richness in the world. At 164 feet (50 meters) deep, with water around 55 degrees Fahrenheit (12 degrees Celsius), the lake only boasts a handful of species of fish, none of which are native to the lake, except the Fat Catfish.

“We think that the Fat Catfish is probably still alive, but [living] in other microhabitats in the depths of Tota Lake,” said Caballero. “We don’t know [for certain], but we will try to look for this species in Tota Lake and surrounding areas in other lakes and lagoons from the Altiplano Cundiboyacense.”

Charting the course of how the  Fat Catfish was lost to science, has meant the team has reexamined historical events that may have impacted the fish. Lasso’s and Caballero’s preliminary visit to Lake Tota in June 2023 builds on the findings  of a social research team from the organization Ictiología y Cultura who studied the historical and cultural significance of the lake for the surrounding communities and visited the region in 2022 to interview locals about the Fat Catfish.
 
The Altiplano Cundiboyacense is a plateau that has been the homeland of the Indigenous Muisca-Guanes peoples, since before Spain colonized Colombia. The Muisca, believed a monster lived in the waters, whale-like, black, with a bull for a head, and as a result didn’t fish in the lake.  But by the late 1800s, after the lake was fully mapped, fears of a lake monster faded.

One possibility for the disappearance of the Fat Catfish is trout farming on the lake, which started in 1939, less than two decades before the catfish’s last confirmed sighting.  Trout farming was originally an economic project promoted by the Liberal government in Colombia during the 1930s, and it’s still a source of income for many local families. Trout are voracious and they eat other fish, which could have proved problematic for the Fat Catfish. 
 
“That is one of the hypotheses of why it was lost, supposedly,” said Caballero. “We still don't know.”

Trout don’t live in deep water, but ichthyologists think that the Fat Catfish may live in the deepest parts of the lake, meaning it’s possible that the two species could coexist in the lake. 

“That's one of the hypotheses that we are trying to test,” says Caballero. 

Even though trout were introduced to Lake Tota, they haven’t overrun the lake. Researchers typically only see them in particular areas, which has also made it less clear if trout had anything to do with the disappearance of the Fat Catfish.

The social research team also found that the Fat Catfish is not widely known in the region and perhaps was never common. Only a few individuals in the Lake Tota region told the team they had seen it in ravines in the area or stuck in hoses coming out of their homes. One person said they caught it from the lake, cooked and ate it, confirming that its bones melted into oil when fried.
 
Using the social research results, Lasso and Caballero, with the help of local guides, identified  five different locations, including Lake Tota during a preliminary visit to the region in June to test for evidence of the Fat Catfish. In August, the team will use environmental DNA kits to attempt to find traces of  the Fat Catfish by examining water samples from each site. In Lake Tota, they’ll take samples from different depths. However, it is difficult to identify traces of DNA in water samples from a fish that has never been genetically sequenced.

“There’s around 10 Fat Catfish specimens in museums here in Colombia and in London and a few other places in the world, but all of them are in formalin and formalin damages the DNA,” said Caballero. “Basically, we cannot access genetic material from these specimens.” 

The search team will have to work backwards with each water sample, first identifying all of the other fish species in each location by the DNA the fish have shed in the water.

“Then if we find something that is different enough from the species that are described for this lake and for which we can access their genetic information, then we can say, ‘Oh, there's something else that is quite likely the Fat Catfish,’” says Caballero.
 
Lasso says the team also plans to use techniques such as electrofishing in creeks and tributaries (a technique scientists use to find and count fish that doesn’t harm them), hooks and lines, trawl nets and small traps in the deeper parts of the lake when they come back in August. Both he and Caballero expect to gather lots of information about the ecosystem and its species, regardless of finding the Fat Catfish or not.

“It’s kind of an adventure but it is what science is about, trying to answer questions and clarify mysteries,” said Caballero. “It’s a big mystery. It would be great if we can find the fish, but we can't have any expectations because otherwise we'll get really bummed out if we can't find it. It's just, ‘Let's try and see, let's give our best, let's try and do the techniques that we know how to do and see what happens.”

As with any hunt for lost treasure, the organizations supporting the search are excited by the possibility of actually finding the Fat Catfish.
 
“The mystery of the Fat Catfish has really captured our attention,” said Michael Edmondstone, communications lead at SHOAL, which is supporting the search for the Fat Catfish. “Everybody who learns about this strange fish seems to fall under its spell. There are so many unanswered questions about it, and no other species that looks anything like it. We're all tremendously excited by the prospect of searching around for some answers.”

If the fish is found, measures to protect it will need to balance its conservation with the livelihoods of local trout fishers. The search team is collaborating with the local fishermen’s association and the municipal leadership of the communities around Lake Tota, which has been key for researchers so far, and will work with Corpoboyaca, the regional environmental authority. 

“A really amazing part of the search for the Fat Catfish is that it isn’t being done by conservationists and biologists alone,” says Harmony Patricio, conservation manager for Re:wild’s freshwater fish program. “It’s a truly multidisciplinary approach that has brought in social science, historical research and interviews with fishers. It can be really difficult to track down all of that information, but it has been essential for identifying and prioritizing sites to conduct biological sampling, which will optimize our chances of finding the Fat Catfish if it still persists.”

In the end, the search for the Fat Catfish could lead to a better understanding of  the highland Cordillera ecosystem and the role humans can play within it.
 
“Every species within its ecosystem plays an important role,” says Christina Biggs, lost species officer for Re:wild. “Even if it’s not a keystone species, it may support a keystone species, and once one of them is gone the other topples and then the entire system falls apart. Humans depend on these systems for clean water or air or soil to grow crops. They’re all so beautiful. There’s not a culture that doesn’t celebrate its natural resources; they’re part of the things we value as humans. So all species are important. Every single one of them.”