Hidden Diversity in Guyana's Rivers Revealed Through Biologists’ Research

By Julie Wrinn, Chief of Staff, College of Arts & Sciences 

The South American coastal country of Guyana may be 2,800 miles away from Louisville, but in the collaborative world of zoology, it’s not too far for an aspiring Guyanese researcher to know that she wanted to pursue doctoral work with a renowned University of Louisville biologist. Together, they recently discovered a new species of tropical freshwater stingray.  

Devya Hemraj-Naraine (PhD Biology 2026) had served as an undergraduate research assistant for Matthew Kolmann, Professor of Biology at UofL, in 2015 when he was a PhD student himself. After completing her Master of Science at the University of Guyana, in 2022 she joined UofL’s PhD program to continue her studies under Dr. Kolmann's supervision. Both researchers are specialists in ichthyology, a branch of zoology devoted to the study of fish.  

About 400 new fish species are described each year across the globe, each one the product of years of fieldwork, museum collection work, and genetic analysis. To know that what you’re looking at is something new, you need comprehensive knowledge of what has already been discovered. This happens, Hemraj-Naraine explained, in two parts: “The first part is we read a lot of papers, so we have an idea of what existed previously. And the second part is we visit the museum collections that have these specimens and look at the morphology. We look at all the different features that make our species different from all these existing ones.” 

Such sustained commitment over many years demands a passion for knowledge that lies at the heart of scientific discovery. Only a few hundred researchers are capable of doing this taxonomic work, and each new discovery represents a meaningful career achievement. As Kolmann elaborated, “You have to know where the species are, and you have to know how many species there are. Just that foundational work is so hard. We spent four years observing species in the Canje River.”  

One of the rewards of discovering a new species is the privilege of naming it. As Hemraj-Naraine explained, “Invariably, we will try to name it based on the place that we collected it or something that is a tribute to the people of the land or the river name or something that comes back and ties back in with this new species and where it was described.” She chose to name this new species after the indigenous Akawaio name for stingrays, “siponinmorok,” as its holotype was found in the coastal regions of Guyana where the indigenous Akawaio tribe lives. A “holotype” is the single specimen that embodies that new species, which is preserved through embalming and stored in a museum of zoology. Hemraj-Naraine's paper about Potamotrygon siponinmorok forms the first chapter of her dissertation (Potamotrygon [“river-ray”] is the genus, like the “Homo” in Homo sapiens). 

Zoologists not only document what species exist; they also document changes in species over time as the climate shifts or catastrophic events occur. States Kolmann, “If there's a dam that's built and it floods an area, the only record of what species existed there are in these museum collections.” Further, it’s critical to have a given species represented in multiple museums, because catastrophic events can also occur to the museums themselves, as with the fire at the National Museum of Brazil in Rio de Janeiro in 2018 that devasted collections. 

Hemraj-Naraine and Kolmann have made multiple expeditions to Guyana’s eastern and central regions to document the biodiversity of the Canje and Demerara Rivers, the latter being where the P. siponinmorok holotype was found. The landscape there transitions from gallery forests to savannas, with a corresponding shift in the mix of fish species. “We didn't even know what we could expect to find in Guyana up until four years ago,” said Kolmann. “Another neat thing about this species is that it's found right in the capital [Georgetown], a few miles from the airport.” Remarkably, this ray (a close relative of sharks) lives entirely in freshwater habitats like rivers and lakes.  

One might assume that various nearby rivers in this region would have significant overlap of species, but their work challenges this assumption. As Kolmann explained, “What Devya's published work found is that the rivers right next door to the Canje . . . shared just 30% of the species with either of those rivers. So, in what is basically just a day's walk, you can have a totally different group of species.” 

Documenting both the diversity and endemicity or a region are critical for effective stewardship. Kolmann said, “One in every three species of sharks and rays is threatened with extinction, according to The International Union for Conservation of Nature (IUCN).” In this region of Guyana, Hemraj-Naraine and Kolmann have found both more diversity (total number and relative abundance of species) and more endemicity (species that are native to only a highly defined area, such as a single island, mountain range, or isolated body of water) than they expected. These conclusions inform decisions about what needs to be protected, in that endemic species are the most vulnerable to extinction based on a catastrophic event in their single habitat.  

Now having successfully defended her dissertation, Hemraj-Naraine works as a curator of fishes at the University of Guyana’s Center for the Study of Biological Diversity; she is also a lecturer there in the Department of Biology. In these roles, she envisions many more expeditions and discoveries: “When I started my PhD, I didn't realize how many [knowledge] gaps there were with the freshwater fish diversity of Guyana and the Guianas. . . . Moving forward, I am going to expand more research in different drainages that we have not extensively sampled over the years. I'm going to continue doing research in Guyana and try to do a few collaborations with some neighboring countries as well.” 

The discovery of P. siponinmorok exemplifies the transformative research taking place in UofL’s Department of Biology. From uncovering previously unknown species to informing conservation efforts and training the next generation of scientific leaders, the department provides opportunities for students to engage in meaningful, internationally recognized research. As Dr. Hemraj-Naraine's journey demonstrates, groundbreaking discoveries often begin with mentorship, curiosity, and the collaborative environment that defines biological research at UofL.