Blind cave catfishes

Over the years, since Hendrickson first came to the University of Texas and told most everyone he met during the job interviews that he would really like to do research on the blindcats living under San Antonio (having done a term paper on them as an undergrad), he’s been trying to do just that. Politics got in the way initially – getting access to the San Antonio wells proved near impossible. The famous political battle surrounding that aquifer and the Fountain Darter, which ultimately brought the U.S. Supreme Court to force Texas to manage the aquifer to assure minimum flows for that endangered fish was raging at the time. It wasn’t too surprising that one high level employee we met with about our request to sample wells controlled by his office was not pleased about the prospect of collecting data that could help add yet another endangered species to the list of concerns his office had to deal with. After complimenting us on all the cool science we hoped to do, his answer was simply “No.”

But, by then, what would become a long and productive connection to Austin’s active community of cavers, landed an icebox of live Mexican blindcats (Prietella phreatophila) in front of his office door one morning, and thus began a long relationship with many people, and that fish species that persists today. As fieldwork in Mexico for that species was winding down, the long-anticipated discovery of it in Texas rejuvenated activity and connections to old friends and colleagues, as well as many new ones. The binational “Blindcat Working Group” formed in 2017 with the mission to work collaboratively to support further studies of the North American blindcats and their habitats as relevant for their protection and sustainability of both these fish species and the humans that depend on the same water.

First meeting of Blindcat Working Group 2017, in the “Neutral Zone” on the international border on Amistad Dam

Participants, First Blindcat Working Group meeting, 25 May, 2017 in the Neutral Zone on Amistad Dam (left to right): Pepe Davila Paulín, Comisión Nacional de Areas Protegidas (CONANP) – Director, Area Protegida Sabinas; Roberto Enriquez, Engineer, CILA; Jean Krejca, President, Zara Environmental, LLC; Juan Antonio, CONANP Park Ranger; Peter Sprouse, Vice President, Zara Environmental LLC.; Andrew Gluesenkamp, San Antonio Zoo; Gary Garrett, University of Texas at Austin; Dean Hendrickson, University of Texas at Austin; Javier Ochoa Espinoza, CONANP – Sub Director, Area Protegida Maderas del Carmen; Ricardo Olivo Rodríguez, CONANP – Area de Protección de Recursos Naturales 004 Don Martín, Biologist; Joanny Guindin, National Park Service – Amistad National Recreation Area, Biological Technician; Jack Johnson, National Park Service – Amistad National Recreation Area, Integrated Resources Program Manager; Christopher Ryan, National Park Service – Superintendent, Amistad National Recreation Area; Sarah Howard, National Park Service – Amistad National Recreation Area

During our 1990s expeditions througout Coahuila chasing Mexican Blindcats, we also went further south in search of Prietella lundbergi, which we knew at the time was being described on the basis of a single specimen. After three cave diving attempts at the spring where recreational cave divers literally stumbled upon that one specimen that they took to the fish guys in their home town at Florida State University, we eventually found blindcats not too far north of the type locality at Nacimiento del Río Frio. Surprising, since that’s right in the middle of the range of the incredibly well studied blind cave Astyanax, making us wonder how all of those working on that species had missed it. Our precious new specimens quickly landed in the field for liquid Nitrogen for DNA studies, and at the time we had little doubt – being so close to the type locality, they just had to be P. lundbergi. Their DNA surprised us, though, and our publication on that pointed out they should probably not even be in the genus Prietella. Unfortunately, the holotype of P. lundbergi was preserved in formalin, so we have no DNA from it, and the DNA results made us want to know more about its morphology than could be discerned from that one precious specimen. Our first attempts to CT-scan the holotype, in the early days of that technology, were not very productive – not enough resolution in the CT data back then. But, with the amazing results from our more recent work on the CT scans of Satan, it was clear we needed to try again. Wow! The new high resolution CT-scans of both the holotype and the largest of the four specimens from Nacimiento del Río Frio are pretty amazing and our first quick inspection of them has us diving in deeper (no pun intended). If our first impressions hold, Prietella lundbergi will likely end up in its own monotypic genus. The morphology revealed in those scans illustrates some synapomorphies with Prietella phreatophila, and a number of similarities to Satan, but many characters say it’s not a member of that genus either. Stay tuned for more news about the relationship of Prietella lundbergi to the rest of the North American blincats.

Prietella phreatophila – live specimens from Amistad National Recreation Area, Texas (photos by Jean Krejca)

October 16, 2021 – Mexican Blindat is the focus of a great mural in Del Rio, Texas. Thank you Del Rio and Center for Biological Diversity (and Andy Gluesenkamp for this photo from the unveiling party).

Hendrickson’s work with Mexican blindcats and many collaborators on both sides of the border goes way back, starting with serious explorations of caves throughout northern Coahuila and Tamaulipas in the 1990s and early 2000s to learn more about both Prietella species. Unlike the deep Edwards Aquifer blindcats, humans can at least access the habitats of both of these, but only by rappeling into some deep caves, and then sometimes SCUBA diving after getting off rope. As a result of those explorations, we now know (Hendrickson et al. 2001) of at least 10 caves or wells where Prietella phreatophila lives, or, from what local residents tell us, where they used to be found in recent history, and much later they finally turned up in Texas too (as we long suspected). Morphology and unpublished DNA sequences both indicate the Texas and Coahuila specimens are of the same species, adding more evidence to support management of the Edwards-Trinity aquifer as binationally shared between the U.S. and México. 

With support from National Park Service, we continue to explore caves on Amistad National Recreation Area, where the new discovery was made. We’re hoping to get back to sampling in Coahuila soon to re-assess how the species is doing there, and to get more DNA samples for more detailed population genetics analyses that should help us better understand the fish, and better assess the true extent of its internationally shared aquifer. We are currently working on a manuscript that provides a range-wide conservation assessment for P. phreatophila. We published one of our presentations about that here.

Satan eurystomus – Widemouth Blindcat (top – specimen is TNHC 21702) and Trogloglanis pattersoni – Toothless Blindcat below (middle – specimen is TNHC 21701). Both specimens held by University of Texas Biodiversity Center (Texas Natural History Collections). Photographs by Garold Sneegas (used with permission). The short movie below them is of the only blindcat ever known to survive being brought to the surface via a well. It was captured in the late 1970s by Dr. Glenn Longley, who kept the specimen alive in a well-fed laboratory at Texas State University in San Marcos, Texas. More detail on the specimen is available in his report (1979). Longley gave this digital copy of the original Super 8mm movie to Hendrickson in the late 1990s. Please cite these images/movie with the details provided here if used elsewhere.

Note: updates relevant to these species may be found in the parent page for blindcats.

The deep pool of the Edwards Aquifer under the city of San Antonio supports not only a large and diverse human population that drinks its water, but also supports a remarkable subterranean aquatic ecosystem, likely the most diverse one in the world (Longley 1981). At the bottom of that ecosystem’s foodchain are a bizarre little eyeless, toothless, pink suckermouthed catfish, Trogloglanis pattersoni, the fungal or bacterial mat it grazes, and there’s a large number of diverse invertrates similarly adapted to the depth and darkness, that probably fall in the middle of the food chain. At the top of trophic system is Satan eurystomus, a toothy, predatory catfish with a wide mouth well designed to gulp in all of the many species of invertebrates (and probably small Trogloglanis as well). The biologists who described these bizarre fishes in 1919 (Trogloglanis) and 1947 (Satan), erected a new genus for each, recognizing their extreme morphological divergence and adaptations to their amazing habitat over immense periods of subterranean evolution. Trogloglanis means troglobytic (cave dwelling) catfish, and the species was named after the biologist who supplied the first specimen. The other genus recognizes the species’ amazing, deep subterranean habitat (and perhaps its evil-looking, toothy gape), and the species name recognizes its impressively wide mouth. 

The original description of Trogloglanis mentioned that blind catfishes were well known to issue from deep (300+ meters) artesian (natural pressure, so not requiring pumping) wells in the San Antonio area. Satan was described nearly 30 years later from very similar wells, and some wells have produced both species. Decades later, a systematic sampling program (Longley and Karnei 1979a and 1979b) found Trogloglanis to be markedly more abundant than Satan, and provided a solid inventory of the system’s diverse invertebrates and their relative numbers. Recent attempts (Zara LLC 2010 and 2014) to replicate the sampling of the late 1970s caught Trogloglanis, but not Satan, and reported most of the invertebrates recorded in the 1970s, though some of those also seemed to have changed in abundance. Analysis of the highly unusual length frequency graph for both species provided by Langecker and Longley 1993, combined with Zara’s conclusion nearly four decades later that Satan may be more rare now than in 1978, and Trogloglanis more abundant, combine to suggest multiple hypotheses about the population dynamics of what are almost surely predator and prey species. Such hypotheses could be testable using recently collected specimens to produce updated length-frequencies.

All wells producing these fishes are relatively near the “badwater zone” of the aquifer (https://doi.org/10.1130/2019.1215(12)), which likely provides the unique biochemical environment that has contributed to the evolution of these fishes. One would think that the very remote, deep and massive Edwards Aquifer that these fishes inhabit, and that San Antonio depends heavily upon for high quality municipal water, would be relatively hard to impact. However, the evidence to date supports the hypothesis that its biotic community has changed, and the “badwater line” that these fishes are close to (and upon which they may be highly dependent), is a complex, microbially-mediated evnironment potentially susceptible to changes in response to water level variations, which are heavily influenced by humans’  management of the system and climate change. The general biotic health of the still very little-studied deep aquifer ecosystem merits further investigation, especially since its health is clearly linked to the health of the human population above it that depends on the same water.

These are both relatively small catfishes, compared to other members of the family.  Langecker and Longley (1993) reported that the standard length of the 47 known specimens of T. pattersoni ranged from 16 mm to 89 mm and the 28 known S. eurystomus measure from 30 mm to 117 mm. Very little is known of their reproductive biology, but the only dissections (also by Langecker and Longley 1993) found no evidence of mature gonads in six specimens of Satan (51-90 mm), but as many as “200 oocytes at different stages of maturation (largest 0.5 mm)” in an 80 mm Trogloglanis and those >60 mm frequently had minute eggs. As for food habits, Trogloglanis stomachs contained only a mud-like substance and Satan‘s stomachs also contained crustraceans. 

Conservation status of these rare fishes is debated. Most every non-govenmental list of threatened and endangered fishes (most recently that of the American Fisheries Society, Jelks et al. 2008) includes both, and there have been petitions to U.S. Fish and Wildlife Service to list both as endangered. The low number of specimens compared to other species tends to give the impression of rarity, but  the response to those petitions has been that there’s inadequate information available to make a determination. In the latest (1994) review, the status of both was declared “Unknown”,  which is defined as “…for those species where additional survey work is required to determine their current trends.” Those determinations were made well before the most recent surveys that failed to detect Satan were done, and the results of those certainly give reason for pause. A re-assessment of the conservation status of both of these species is overdue, as the Center for Biological Diversity recently pointed out in a lawsuit.

Rarity and condition of specimens has inhibited research on these species for years, and so it’s not surprising that the phylogenetic history of the two Edwards blindcats is still only vaguely know. Only 14 specimens of Satan can be found in the world’s museums, and all were preserved in formalin, which prevents DNA extraction.  Simlarly, DNA from Trogloglanis was unknown until a small specimen from the recent surveys (now in our collection as TNHCi 42586) provided tissues from which we sequenced DNA and also got a nice CT scan (see images below) . While the Cytochrome B sequence obtained from that specimen has not yet been fully analyzed, it has provided some surprises that require further research. More recently, tissue from the same specimen was used to extract its complete genome (Pirro, Stacy. 2020. “Trogloglanis Pattersoni – BioSample – NCBI.” NCBI Resources. April 18, 2020. https://www.ncbi.nlm.nih.gov/biosample?LinkName=bioproject_biosample_all&from_uid=626086.). 

With failure of the recent surveys to produce DNA of Satan, we turned back to anatomy for insights into its evolutionary history. CT scanning, an amazing and non-destructive tool for examining osteology of such rare specimens, has greatly improved our knowledge of this species anatomy. Our paper (published on Halloween 2017) with detailed illustrations of Satan‘s skeleton discusses what CT scanning revealed about the species’ evolutionary history. In the same paper we published many animations of Satan‘s skeletal anatomy that can be found in our blindcat Morphosource project and in the collection of supplemental files for the paper that we permanently archived in UT’s ScholarWorks. Satan is also a topic in most of the presentations from our mini-symposium on blindcats at the 2017 Joint Meeting of Ichthyologists and Herpetologists that we hosted here in Austin.

But, despite all the new morphological insights, not unexpectedly, the true evolutionary history of this diabolic critter remains elusive.  We won’t stop hoping to get a sample of Satan‘s DNA, and if we ever do, we’re well prepared, having DNA of all of the other three regional blindcats, to get much closer to the truth. And, if we ever do obtain DNA of Satan, that would allow us to use a new, very powerful tool for monitoring the species by looking not for specimens, but simply for its DNA in water.  DNA of many of the incredibly biodiverse ecosystem of the deep Edwards Aquifer can be much more easily obtained than might be the case for Satan, and it’s clear that the stability (or lack thereof) of that biotic community has great potential to serve as an indicator of the overall health of that ecosystem that, like humans, also depends on the continued high quality of the Edwards’ water. With evidence mounting that the deep and remote world has been changing under the influence of humans and climate change (https://doi.org/10.1130/2019.1215(13), https://doi.org/10.1511/2019.107.5.260), we hope that those charged with managing that important resource promote research of its biota to help provide the best information possible to assure sustainable management of that strategic water supply for both humans and the aquifer’s amazing biota.

Satan eurystomus in Fishes of Texas Project – map, species account, specimen list, blog post about the species and its habitat

Trogloglanis pattersoni in Fishes of Texas Project – map, species account, specimen list