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Treasures of the Sierra Madre: The Fishes of the Upper Río Pánuco, Mexico

by TFH Magazine on April 6, 2012 at 10:30 am

Monetzuma swordtail (Xiphophorus montezumae). Photograph by Gary Lange.

By John Lyons

The stereotype of Mexico is that it is a land of deserts and cactus. Certainly much of the country is arid, but Mexico has a surprising amount of water features that support a diverse number of unique fish fauna. Unfortunately population growth and increasing industrial and agricultural development are degrading these waters at an alarming rate, particularly in the central part of the country. Scientists warn that many of the fishes of central Mexico are in grave jeopardy of extinction.

Fortunately a few areas of central Mexico retain aquatic ecosystems that are largely intact. These areas serve as important reservoirs of biodiversity and reminders of what will likely be lost from the rest of region. One such area is the upper portion of the Río Pánuco basin, located in a rugged, sparsely settled part of the Sierra Madre Oriental mountains, about 200 to 300 kilometers north of Mexico City. The fishes of this part of the Pánuco are little known outside of scientific and specialized aquarist circles, but they have great potential for becoming a part of the broader aquarium hobby.

I had the opportunity to visit the upper Pánuco in February 1999 and assess the status of some of its waters and fishes. I was accompanied by Dr. Henry “Hank” Bart, who is the director and curator of fishes for the Tulane University Museum of Natural History in New Orleans, and Norman Mercado-Silva, who at the time was finishing a thesis on the fishes of the upper Pánuco for his biology degree at the National Autonomous University of Mexico in Mexico City and is now a Research Specialist with the Arizona Cooperative Fish and Wildlife Research Unit, School of Natural Resources.

Journey to the Upper Pánuco

The journey to the upper Pánuco was full of contrasts. We began in Mexico City, one of the most densely populated valleys on Earth. I’d driven there once before, and that was enough; Norman took the wheel. For an hour he nonchalantly battled the relentless traffic of the city until we finally crested some low hills and gradually emerged into a more agricultural landscape. The air cleaned and the traffic thinned. We passed occasional irrigation ditches and small, nearly dry, earthen ponds, but natural streams were absent. After three hours we reached the pleasant colonial city of Querétaro, where we had lunch and stocked up on beer for the days ahead. Then at last we headed into the Sierra.

Immediately the land became noticeably drier, almost desert-like, and nearly devoid of people. The vegetation was mainly cactus and thorny scrub. The sun was bright and hot. At some point we crossed from the Río Lerma watershed, which drains into the Pacific Ocean, into the Pánuco watershed, which drains into the Gulf of Mexico, but the change was almost imperceptible because the few stream courses we crossed were dry and choked with sand. A handful of small permanent springs occur in this part of the Pánuco basin, but they support only two highly tolerant species, the Mexican tetra (Astyanax mexicanus) and the dusky goodeid (Goodea atripinnis gracilis).

Dusky goodeid (Goodea atripinnis). Photograph by Scott Buckel.

The road began to climb. It wound back and forth up stony canyons and along rocky outcrops. There were magnificent views, but the occasional trucks that barreled toward us from around blind curves discouraged sightseeing. I took over the driving, but Norman and Hank quickly decided that they felt safer in Norman’s experienced hands. As they tactfully put it, they preferred that I “enjoy scenery from the passenger side.”

As we climbed higher the air became cooler and more humid, and the character of the land changed rapidly. Trees replaced cactus and soon we were driving through pine and oak forests interspersed with mountain meadows. Once we crested the western-most range of the Sierra, the landscape became even lusher. This slope intercepted the rain clouds that came off the Gulf of Mexico, leaving little moisture to reach the other side of the mountains. For the first time on the trip we could see natural streams. But this high up the streams were so cold that they could only support only introduced rainbow trout Oncorhynchus mykiss. As night fell we descended toward warmer climes and a good night’s sleep in the valley of the Río Sana María.

Collecting in the Río Jalpan

The next morning we began our fish surveys. We started on the Río Jalpan, a tributary of the Santa María, about 15 kilometers north of the town of Jalpan along Mexico Highway 69. Since this was the middle of the dry season, the river didn’t have much flow, and you could hop across the riffles on rocks without getting wet. But the pools were still over my head. Big cypress trees lined the banks and made for a picturesque scene, marred only by some piles of garbage along the river bank next to the road.

We could see cichlids in the depths among the cypress roots, but there was no way that we could catch them. However, we seined the edges of the pools and caught other fishes. Most common were the ubiquitous Mexican tetra, the Atlantic molly (Poecilia mexicana), and the porthole livebearer (Poeciliopsis gracilis). The Atlantic mollies were particularly attractive. Females had bright yellowish orange anal fins and orangish speckling on light bluish-gray flanks. Males were more intensely colored, with orange and black anal, dorsal, and tail fins and a darker bluish black body.

Porthole livebearers were distinctively marked with a row of spots along their sides, but had little color. This species is native to southern Mexico and Central America, but has recently become established within central Mexico. In rivers south of Mexico City the introduced porthole livebearer has become abundant and has been blamed for the decline of several native species, so its occurrence in the Pánuco was ominous.

Porthole livebearer (Poeciliopsis gracilis). Photograph by Horst Linke.

 

Hank was most excited about our capture of two small, nondescript juvenile fleshy-lip buffalofish (Ictiobus labiosus). Hank is a specialist of the buffalofish, the subfamily Ictiobinae within the sucker family Catostomidae. Buffalofishes are bottom dwellers found mainly in rivers. They often reach large sizes and are important food fish in some areas. Various buffalofishes occur from Canada to Guatemala, but the exact number and identification of species within the group is problematic, particularly in Mexico. The fleshy-lip buffalofish, found only in the upper Pánuco was first recognized and described in 1904, but since then very few individuals have been collected for scientific study and almost nothing has been learned about the species’ biology. The main purpose of Hank’s trip had been to obtain fresh specimens for genetic and morphological analyses. And he was successful at our first site!

Success in the Río Santa María

After celebrating our find with a hearty breakfast of soda and cookies from a roadside stand, we moved onto the Río Santa María proper at the Highway 69 crossing near the pretty little town of Conca. Here the river was wide and fast flowing, gathering force before it plunged into a rugged and spectacular canyon to the east. As it was a Saturday, families were picnicking and camping on gravel bars along the river. Several were curious about the nets we carried, and offered well-meaning advice (and a few friendly jibes) about how and where to catch fish.

However, despite their suggestions, we caught nothing at first. Where we started the current was too strong and there were no hiding places for the fish. Only when we moved to a boulder-strewn shoreline with slower water did we have success. Initially we encountered a few Mexican tetras and porthole livebearers, and then caught nearly 40 small juvenile fleshylip buffalofish in a single haul of the net. Hank was ecstatic. We ended our sampling with a small Pánuco catfish. This species is found only in the Río Pánuco basin, and grows large enough to be an important food fish for local fishermen. But other than that, scientists know almost nothing of its biology. Unfortunately, this last statement applies to most of the species we encountered during our visit.

Sampling the Río Calabazas

After a quick stop in Conca to call home, we headed towards the town of Río Verde, which was to be our base for the next couple of days. I was beginning to feel pretty queasy, a common occupational hazard for me during my years of work in Mexico. Norman was beginning to have doubts about my norteamericano constitution, as the last time I’d been to Mexico he’d had to spend hours calling doctor friends and visiting pharmacies in order to get my insides to a point where I could endure my overnight flight back to the states. But I thought I could manage sampline on more site, the Río Calabazas, a tributary of the Río Verde.

The Río Calabazas at the Highway 69 crossing was wide, shallow, sandy bottomed, slow-moving, and full of aquatic vegetation. Two species of cichlids were common and relatively easy to catch, the black cheek cichlid (Herichthys labridens) and the Río Grande cichlid (H. cyanoguttatus). The Río Grande cichlid is a widespread species native from Texas to the lower part of the Pánuco basin, but it has been introduced into the Río Verde system. Some aquarists consider Río Pánuco populations to be a separate species, H. carpintis. We also captured numerous Pánuco mosquitofish, a small grayish livebearer, and Atlantic mollies. The mollies here were colored differently from those in the Río Jalpan, having less orange in their fins and lighter, more bluish flanks.

Black cheek cichlid (Herichthys labridens). Photograph by Don Conkel.

Enjoying the River at “Las Cascadas”

We made it to the town of Río Verde before my stomach revolted, but just barely. Fortunately my illness proved to be nothing more than a garden-variety case of turista, and by the next morning I felt much better. Nonetheless we started the day off slowly and didn’t reach our first stop, the Río Tamasopo, until almost noon.

We sampled the river at “Las Cascadas” near the town of Tamasopo. Here the river roke into numerous small channels that flowed over a sharp 15-meter high escarpment, producing a series of lovely waterfalls. At the base of each of the falls was an inviting deep blue pool. In the interests of science we decided to conduct a swimming and diving survey of the largest of these pools. We could see schools of cichlids in the deep water and brilliantly colored Atlantic mollies in the shallows. If we stood still, Mexican tetras would nibble at the hairs on our legs. But the pools were too deep and rocky for our nets, so we moved to one of the outlet channels to collect fish.

Even though the water was slow and shallow and we could see lots of fish, our capture rate was low. The fish were wary and fast, darting under boulders as soon as our nets approached. It took a lot of splashing and stumbling to get a decent sample of the fauna. But the effort was well worth it. In addition to the expected Mexican tetras and Atlantic mollies, we caught Tamasopo cichlids (Herichthys tamasopoensis). This species is closely related to the Río Grande cichlid.

Río Grande cichlid (H. cyanoguttatus). Photograph by Aaron Norman.

We also collected three Monetzuma swordtails (Xiphophorus montezumae) which was my favorite species of the trip. This type of swordtail is relatively deep-bodied and robust, and the male has a particularly long sword. Both sexes have an attractive spotting pattern and nice yellow-green coloration on their fins and flanks.

Collecting in the Remote Río Gallinas

It was hard to leave the scenic and relaxing atmosphere of the Tamasopo, but we needed to also sample the Río Gallinas into which the Río Tamasopo flows. Where Highway 70 crossed the Río Gallinas there was no access, so we headed off on a dirt road through a sea of sugar cane fields to find a way down to the river. After blundering about for a while and following some confusing directions from the locals, we found a place where we could get into the water. The river here was wide with lots of boulders and logs, and sampling was challenging. But after a half hour of battling slippery rocks, hidden drop-offs, and shoreline brambles, we were rewarded with a nice pair of Montezuma swordtails, a couple of Tamasopo cichlids, a single Pánuco mosquitofish, and ten pretty Atlantic mollies.

Dusk was approaching, so we hurried off to the nearby town of Ciudad Valles so that Hank and Norman could canvas the fish vendors at the market about the availability of large specimens of buffalofish. I stayed with the truck, studying the map and contemplating dinner options. They soon returned, disappointed because the vendors apparently never saw buffalofish. To cheer them up, I suggested a special dinner of carne asada a la tampiqueña, steak Tampico, one of my favorite dishes. Norman began to ask if I had found out about a good restaurant there in the Ciudad Valles, and then stopped and sighed when he figured out what I had in mind. By now he was getting used to my occasional crazy ideas. “Let’s head right to where it originated,” I said. “Tampico’s only three hours away on the coast.” So off we went, out of the mountains and onto the coastal plain in the gathering darkness. It was a great ride, and really gave us a better perspective on the entire Pánuco basin. But I never got my steak Tampico; the roasted goat on the menu looked too good to pass up.

Final Day at Laguna Media Luna

The next day was our final one in the upper Pánuco basin, and Norman has saved the best location for last, Laguna Media Luna. This deep, crystal-clear lake, located a few kilometers outside the town of Río Verde, was fed by a series of beautiful blue hot springs that kept its temperature a constant 29°C (84°F). The lake is the closest thing to a freshwater coral reef that I’ve ever encountered, with its warm, clear water, thick, coral-like aquatic plant growths, and teeming schools of multicolored fishes.

Near shore were clusters of Atlantic mollies and Tamesi mollies (Poecilia latipunctata). The Atlantic mollies looked similar to those from the Río Jalpan, whereas the Tamesi mollies were less colorful but still very attractive, having a series of dark spots that formed a sort of jagged black lateral stripe on a silver background. Tamesi mollies are native to the lower Pánuco but have been introduced into the Laguna. In midwater were vast aggregations of curious Mexican tetras. Near the bottom a few tessellated pupfish (Cualac tesselatus) could be seen. They are a shy but appealing species with a brilliant spangling of white spots on silver gray flanks. This species in endemic to the lake and surrounding springs and canals; that is, it is found nowhere else on Earth.

However, the stars of the lake’s fish fauna were clearly the cichlids. Four cichlids were presented, two introduced species that were uncommon, the Río Grande cichlid and the Mozambique tilapia (Oreochromis mossambicus), and two native species that were abundant, the black cheek cichlid and the Media Luna cichlid (Herichthys bartoni), which is endemic to the lake and surrounding valley. The blackcheek cichlid came in at least three different color patterns, ranging from nearly all black to a two-tone white back black belly to mostly greenish with black blotches on the sides. The Media Luna cichlid had at least two forms, one with a bright white back and blackish sides and belly and the other with a greenish body, bluish lips and gill covers, and blackish mottling on the sides.

We did not have permission to collect fish within the lake proper, which is a refuge area, so after two hours of blissful snorkeling, we reluctantly moved to one of the outlet irrigation canals from the lake and began sampling. These canals were artificial and lined with concrete. Once we entered one of them, we knew we’d made a mistake. The water was chest deep and the current was very strong. Worse, the bottom was coated with algae and very slippery. It was difficult to stand upright, much less climb up the steep canal walls to get out. When we unrolled our seine to sample, it acted like a sail and we were dragged down the canal by the current. It was a comical scene, at least from Norman’s perspective on the bank.

Sampling wasn’t very productive, although we did take a few Mexican tetras and black cheek cichlids, and one tessellated pupfish. After several splashy failures, we managed to exit the canal with Norman’s help. The last of our beers tasted pretty good at that point.

That was our final fish collection in the upper Pánuco system, and soon thereafter we left the Pánuco basin and went our separate ways. We’d had a great trip, and we’d encountered some fascinating fishes. It was heartening to see that the upper Pánuco still harbored generally healthy stream systems, although we’d seen enough pollution, habitat destruction, and introduced species to make us nervous.

The sites we visited emphasized the tremendous aquatic diversity that still remains in Mexico, and underscored the urgency of improved environmental protection in this rapidly growing nation.

Posted in TFH Extras by TFH Magazine on April 6th, 2012 at 10:30 am.

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