Cave fauna fascinates young and old alike. Deep within the karst systems of Chapada Diamantina, Brazil, lives one of the world’s most diverse groups of cave-dwelling fish.
In fact, Brazilian cavefishes are the richest troglobitic (cave-dwelling) ichthyofauna worldwide, boasting 13 different genera. While the surface world is teeming with life, the subterranean realm, or the hypogean habitat, demands a very specific set of skills to survive.
The research, conducted by Thalia Rodovanski (from the Departamento de Biologia, Universidade Federal de São Carlos, Brazil) and her team, was published in Subterranean Biology and took a closer look at the Copionodontinae, a subfamily of primitive catfishes.

Building on previous findings regarding the aggressive (agonistic) nature of Copionodontinae species, the researchers used this behavioral foundation to investigate how their physical and sensory structures have evolved in response to their environment.
By comparing surface-dwelling (epigean) species such as Copionodon pecten, C. lianae, and G. rodriguesi with their cave-bound cousin, Glaphyropoma spinosum, the researchers undertook the task of uncovering how these fish transitioned from the sunlit rivers to the pitch-black cave riverine systems.
Specifically, they did this by measuring the brain morphology and sensory structures such as barbels, eyes and counted pores of the lateral canal system on the head.
The curious findings
One of the most striking finds involved the genus Glaphyropoma. While the cave-dwelling G. spinosum shows classic troglomorphisms (adaptations for life in constant darkness), such as reduced eyes and a loss of skin pigment, the researchers found something surprising: even the surface-dwelling species in this group showed eye asymmetry and reduction.

Based on this, the researchers hypothesized that the asymmetry in the eyes is a plesiomorphic character (an ancestral trait) of the genus, rather than a feature developed in response to the specific habitat of each species. This pre-existing condition likely favored the colonization of hypogean (underground) habitats by G. spinosum.
In other words, Glaphyropoma already had a tendency toward reduced eyes. Instead of evolving small eyes because of the cave environment, they likely had them from the start. This is known as exaptation: a trait that originally evolved for one function (or no function at all) and was later co-opted for a new, different purpose, in this case, better suited for the dark.

As you can imagine, seeing in pitch black is quite hard. Therefore, these species had to rely on their other senses. The study found that the cave-dwelling G. spinosum has a longer telencephalon than its relatives. This is significant because it is the part of the brain responsible for navigating through chemical cues, creating mental maps (spatial memory), and participating in social interactions. Interestingly, the mesencephalon (the vision-processing center) hasn’t shrunk significantly yet, suggesting that these fish are still in the middle of their evolutionary transition.
The researchers concluded that while G. spinosum shows clear cave-specialized traits, many of these features are shared by its surface-dwelling cousins.
However, because of a lack of specimens of G. rodriguesi, the only known epigean species of the genus, which occurs sporadically in caves, it is not yet possible to definitively conclude if the sensory troglomorphisms detected in this study are related to taxonomic identity or the habitat itself.
Ultimately, such research is key to understanding more about the complex life of the highly specialized species that inhabit these fascinating environments.
Original source:
Rodovanski T, Bichuette ME, Cetra M, Mattox GMT (2026) The influence of subterranean habitats in the sensorial and brain morphology of hypogean and epigean Copionodontinae catfish (Siluriformes, Trichomycteridae). Subterranean Biology 55: 27-42. https://doi.org/10.3897/subtbiol.55.175751








































