image: The beauty of Hypancistrus zebra (Loricariidae), a critically endangered species, heavily demanded by the aquarium trade and threatened by the Belo Monte hydropower plant in Brazil.
Credit: Leandro Sousa
LAWRENCE — Few people on Earth know as much about catfishes as University of Kansas researcher Gloria Arratia, who serves as editor and contributor to the just-published first volume of “Catfishes: A Highly Diversified Group” (CRC Press, 2025), a two-volume reference. While the first volume focuses on the fascinating anatomy of catfishes, the second will focus on their evolution and genetic relationships.
Arratia’s new work, co-written by Roberto Reis of Pontifícia Universidade Católica do Rio Grande do Sul in Brazil, reflects the latest understanding of the family tree of Siluriformes (the scientific name for catfishes), incorporating genetic data from the most recent molecular studies to better represent phylogenetic relationships and including species from understudied areas like Africa and Asia.
Arratia said catfishes have long captured the popular imagination.
“Curiously, catfish often attract people’s attention because of their unusual and sometimes ‘ugly’ appearance,” Arratia said. “This fascination isn’t limited to specialists; ordinary people are also drawn to stories about catfish. Hearing about a fish that has ‘barbels,’ like whiskers, or that lives at night — it gives catfish an air of mystery. People are especially intrigued when they learn that many catfish appear on certain nights, often with the rising of the moon, and others produce sounds and ‘talk’ to each other.”
The first edition of Arratia’s "Catfishes" came out in 2003, but new scientific methods and understanding compelled the researcher to compile a new edition.
“Copies sold out soon, and I began receiving requests from people around the world asking for a second edition,” she said. “Given the many changes in catfish research over 20 years, I proposed a new edition. A colleague, Roberto Reis from Brazil, home to the largest number of catfish species in the world, joined me as co-editor. Brazil has become the global center of ichthyology, with specialists in morphology, molecular biology, parasitology and many other areas. It was logical to bring this expertise into the new book.”
Arratia said the result is not simply an updated edition but an entirely new book, larger than the first, with expanded chapters and a dedicated section on phylogenetic relationships.
“Our understanding of the group has advanced so much that a new work was essential,” she said.
Arratia’s scholarly interest in catfishes stems from first studying them in her home country of Chile, where the two catfish species that dominate freshwater ecosystems are the most ancient of the fish group worldwide.
“I was born in Chile, where there are two catfish groups considered among the most primitive families in the world,” she said. “One family is Diplomystidae, which is endemic to Argentina and Chile. The other, Nematogenyidae, is found only in Chile. As a young researcher, this uniqueness caught my attention, and I dedicated much of my academic work to studying these fishes, which appear and act like ancient catfish would have.”
“I even produced three monographs on Diplomystidae, publishing descriptions of more than 300 pages,” Arratia said. “Anyone studying catfish anywhere in the world — whether in Asia, Europe or South America — must understand these two families to grasp the evolutionary history of catfish as a group. That is how I became deeply interested in them.”
Asked what she found most interesting about the biology of catfishes, Arratia mentioned the “Weberian apparatus,” also found in a larger group of fishes that includes the Cypriniformes (for example, carps), Characiformes (like tetras) and Gymnotiformes or Neotropical electric fishes.
“Located just behind the cranium, the first four to six vertebrae are highly modified,” she said. “In most fishes, vertebrae are relatively simple, consisting of a centrum and associated processes. But in catfish, these vertebrae are modified in connection with the gas bladder. The result is a specialized organ that enhances hearing and balance. Sound vibrations from the gas bladder are transmitted through the modified vertebrae to the inner ear, allowing catfish to detect and interpret sounds more effectively than most other fishes. This system not only improves hearing but also plays a role in buoyancy control. Some catfish can even produce sounds and communicate with one another using the Weberian apparatus and its connection to the gas bladder.”
Arratia said her new work would incorporate research from understudied areas like Africa and Asia, where fieldwork and sampling have been limited, leading to gaps in catfish knowledge.
“Looking ahead, our expectation is that Africa and Asia will produce many new discoveries,” she said. “Research there is only beginning. In Asia, most studies so far have been molecular, with very little work on morphology, even though those catfish are quite different and deserve close study. The same is true in Africa. Most of the research has been concentrated in South Africa and especially on one family, while we know very little about species across the rest of the continent. In general, we still don’t know much about the anatomy of catfish where many areas are just beginning to be explored, like the nervous system and reproductive system, as well as strategies in reproduction and early development. There’s a lot of work to do, especially with species from Asia and Africa — two continents where our knowledge is limited.”
Next up is Arratia’s second volume of the updated edition, due out this October.