ichthyofauna

The Evolutionary Adaptations of Cave-Dwelling Catfish in Brazil

What do brain morphology and sensory structures tell us about the evolutionary adaptations between catfish that live on the surface and those that live in caves?

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.

Shallow water pool in Igatu. Photo credit to Maria Elina Bichuette.

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.

Shallow water pools in Igatu. Photo credit to Maria Elina Bichuette.
Researcher in a cave system in Igatu. Photo credit to Maria Elina Bichuette.

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.

*Copionodon pecten*. Photo credit to Maria Elina Bichuette.

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.

*Glaphyropoma spinosum*. Photo credit to Adriano Gambarini.

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

“Oscar describes Oscar”: Interview with Oscar Lasso-Alcalá, Pt 3

“This is why Mikolji’s Oscar is a highly appreciated species in the aquarium hobby. It is more than just a fish in an aquarium when it is considered a true pet.”

In this last part, we talked with ichthyologist Oscar Miguel Lasso-Alcalá about what makes Astronotus mikoljii – a new to science cichlid species that he recently described in ZooKeys – so special.

Find Part 1 and Part 2 of the interview.

What makes this species so charismatic and loved by aquarists and ichthyologists?

I already spoke about my experience as an aquarist from an early age, where the qualities of the species of the Astronotus genus, known as Oscars are highlighted.

Different varieties and color patterns have been obtained from them through selective breeding, or genetic manipulation, which are called living modified organisms (LMOs) or genetically modified organisms (GMOs).

However, the true lovers of nature, the aquarians of the “Biotope Aquarium” movement and the like, prefer pure specimens to manipulated or artificially modified ones. This is why Mikolji’s Oscar is a highly appreciated species in the aquarium hobby. It is more than just a fish in an aquarium since it is considered a true pet.

For ichthyologists, it is remarkably interesting and at the same time very challenging to study a genus like Astronotus, which already has only three described species (Astronotus ocellatus, A. cassiprinnis and A. mikoljii).

This is an unusual situation, which, as we have reported, requires an integrative approach and the work and experience of different specialists for its study. With all certainty, as in the case of Mikolji’s Oscar, other species of the genus Astronotus remain to be studied and described, and we hope that we will have the fortune to participate with our experience in these new works.

Local people have long known this species. What role does it have in their lives?

It is important to clarify that Astronotus mikoljii is a new species for science, but it is not a “new species” for people who already knew it locally under the name of Pavona, Vieja, or Cupaneca in Venezuela or Pavo Real, Carabazú, Mojarra and Mojarra Negra in Colombia. Nor for the aquarium trade, where it was known by the common name of Oscar and scientific name of Astronotus ocellatus, or, to a lesser degree, as Astronotus cassiprinnis.

This species has been of great food importance for thousands of years for at least nine indigenous ethnic groups.

Much less is it a new species for the nine thousand-year-old indigenous ethnic groups that share their world with the habitat of this fish, who baptized it with some 14 different names, known in their languages as mijsho (Kariña), boisikuajaba (Warao), hácho (Pumé = Yaruro), phadeewa, jadaewa (Ye’Kuana = Makiritare), perewa, parawa (Eñepá = Panare), yawirra (Kúrrim = Kurripako), kohukohurimï, kohokohorimï, owënawë kohoromï” (Yanomami = Yanomamï), eba (Puinave), Itapukunda (Kurripako), uan (Tucano).

Hence, the importance of scientific names, since the same species can have multiple common names, in the same language or in multiple languages.

It is important to note that very few studies that describe new species for science include the common names of the species, as given by the indigenous ethnic groups or natives of the regions, where the species live.

This species has been of great food importance for thousands of years for at least nine indigenous ethnic groups, and for more than 500 years to the hundreds of human communities of locals who inhabit the Orinoco River basin in Venezuela and Colombia. In our studies, in the plains of Orinoco from 30 years ago, we were able to verify its consumption, as well as high gastronomic value, due to its pleasant taste and enhanced texture.

However, due to my imprint as an aquarist, I have not wanted to consume it on the different occasions that it was offered to me, because it is very difficult to eat the beloved pets that we had in our childhood.

Why is this fish important to people and to ecosystems?

It is especially important to highlight that the Astronotus mikoljii species plays a very important role in the ecosystem, due to its biological and ecological background.

Although it can feed from different sources, it is a fundamentally carnivorous species, and therefore, it “controls” other species in the ecosystem.

Without Mikolji’s Oscar, the aquatic ecosystem would lose one of its fundamental links and the delicate balance of its functioning, because the species it feeds on could increase their populations uncontrollably, becoming veritable pests. This would put in great danger the entire future of the aquatic ecosystem of the Orinoco River basin and the permanence of other species of ecological importance.

In addition, it would surely affect other species used by man, both those of commercial importance (sold as food or as ornamental species), and for the subsistence fishing of native and indigenous inhabitants.

Mikolji’s Oscar, although a carnivorous species, also has its natural predators, for example piranhas and other predatory fish. For this reason, it evolved with an ocellus, or false eye, at the base of the caudal fin, to confuse its predators and guarantee its survival. Obviously, this species will be compromised if we don’t learn about it, use its populations wisely and preserve it in the long term.

***

Photos by Ivan Mikolji.

***

You can find Part 1 and Part 2 of the interview with Oscar.

***

Follow the ZooKeys journal on Twitter and Facebook.

Fishy “juveniles” from the Caribbean to be recognized as a new species, the Hourglass basslet

Living in deep reefs in the Atlantic Ocean, the banded basslet, a small and colorful species with a wide range of distribution, has long been thought to undergo significant changes during its growth into an adult. Suspiciously, the juveniles appeared much more heavily banded. Recently, however, American scientists figured out that the ‘juveniles’ were in fact a new species.

In a paper published in the open access journal ZooKeys, Dr. Carole C. Baldwin, Ai Nonaka, Dr. Luke Tornabene, all affiliated with the National Museum of Natural History, Smithsonian Institution, and Dr. Ross Robertson, Smithsonian Tropical Research Institute, Panama, describe two new basslet species discovered in the Caribbean off the southern coast of Curaçao. Their finding comes as part of the Smithsonian’s Deep Reef Observation Project (DROP), devoted to documenting the biodiversity in the poorly studied depth zone of 50–300 m with the help of a special submersible, called Curasub.

Having been previously confused with the banded basslet’s juveniles, one of the new species was discovered after the submersible’s hydraulic arms collected specimens with smaller size and thicker bands from shallower depths. Subsequent study of the specimens revealed additional morphological, as well as molecular, evidence that suggest the specimens represent a new species.

The species is characterized by predominantly white to tan colored body with three vertical blackish bands, one running across its head, and two along the body. The latter often appear hourglass-shaped, with their middles being narrower and lighter. Due to this resemblance, the authors suggest that the new species is commonly called Hourglass basslet, while its scientific name is Lipogramma levinsoni, in recognition of the generous and continuing support of research on neotropical biology at the Smithsonian Tropical Research Institute (Panamá) made by Frank Levinson.

The second new basslet from Curaçao can be distinguished by the three dusky bars likewise running across its head and body. Its ground color is yellow to white, with the bar at the rear being much lighter than the rest. Reflecting its appearance, its common name is proposed to be Yellow-banded basslet, while its scientific identity is Lipogramma haberi, in recognition of Spencer and Tomoko Haber, who funded and participated in one of the submersible dives that resulted in the collection of a paratype of the new species.

In their study, the researchers also point out that it is likely that there are at least two additional cryptic species belonging to the same genus. Those species are currently being analyzed in ongoing investigations of the Caribbean deep-reef ecosystems.

Past discoveries made as part of the DROP Project at Curaçao include adorable fishes such as the Stellate scorpionfish and the Godzilla goby. To recognize all involved in the DROP research program, the team have described the small blenny fish as Haptoclinus dropi, after the project itself, while another goby species, Coryphopterus curasub, bears the name of the submersible used in the dives.

Original source:

Baldwin CC, Robertson RD, Nonaka A, Tornabene L (2016) Two new deep-reef basslets (Teleostei, Grammatidae, Lipogramma), with comments on the eco-evolutionary relationships of the genus. ZooKeys 638: 45-82. https://doi.org/10.3897/zookeys.638.10455