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#11513 Cueva de El Pachón, San Luis Potosí, Mexico

Sponsored by
Educated by Nature

Mexico, San Luis Potosí, Ciudad Valles Municipality

Cueva de El Pachón is a limestone cave located in the Sierra de El Abra karst region of San Luis Potosí, Mexico. Its underground pools and slow-moving streams form one of the best-known natural habitats of the Blind Cave Tetra (Astyanax mexicanus). Isolated in complete darkness for thousands of years, these fish evolved without functional eyes or body pigmentation, making this cave an important site for evolutionary and ecological research.

The habitat consists of clear, mineral-rich freshwater flowing through limestone passages with rocky substrates, gravel, and fine sediments. Aquatic plants are absent due to the lack of sunlight, while organic matter entering from the surface supports the cave food web. This unique subterranean ecosystem inspired the recreation of a biotope aquarium that reflects its geological structure, stable water conditions, and distinctive cave environment.

Submitted by
Shivansh Rajpoot
GPS
22.6096554, -99.0245972
Geographical region
Central America
Drainage Basin
Río Panuco
River catchment
Río Tampaón
Water body type
Pool
Water body name
Cueva de El Pachón
Water body part
Pool
Water body course
Upper course
Water body: tributary of
River
Tributary name
Río Tampaón

Videos above and below water


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Water Chemistry

Water information

Water type
Freshwater
Water color
Clear water
Water transparency
High
Concentration of sediments
High
Water temperature
24 °C
Water flow/curent
Slow

Chemical parameters

pH
7.4
Conductivity
520
GH
180 mg/l
dGH
KH
150 mg/l
dKH
Dissolved Oxygen
85 %

Substrate in nature

Sand
White
Pebble/Gravel
Grey
Stone
White
Stone form
Irregular
Silt/Mud
None
Leaves
None
Driftwood
None
Submerged terrestrial vegetation
None

Aquatic Biotope

Date of collecting
15 May, 2019
Collecting area
Open water
Water depth
over 2,0m
Air temperature
26 °C
Sunlight
No sunlight

Environment

Environment
Untouched
Surrounding area

Cueva de El Pachón is located in the Sierra de El Abra karst region of San Luis Potosí, northeastern Mexico, within the Pánuco River Basin. The cave lies beneath tropical semi-evergreen forests growing on limestone hills. Rainwater infiltrates the porous karst landscape, feeding underground streams and pools with clear, mineral-rich water. The cave maintains a stable environment throughout the year, with high humidity, constant temperatures, and complete darkness beyond the entrance. Organic matter entering from the surface provides the primary source of nutrients for the subterranean ecosystem.

Underwater landscape

The habitat consists of clear underground pools connected by slow-flowing passages over limestone bedrock. The substrate is composed of limestone rocks, gravel, and fine calcareous sand, with very little suspended sediment. Aquatic vegetation is absent due to the lack of sunlight. The Blind Cave Tetra (Astyanax mexicanus) is the dominant fish species, accompanied by cave-adapted invertebrates such as freshwater shrimp. Rock crevices and submerged cavities provide shelter and potential breeding sites.

Fish:

  • Astyanax mexicanus (Characidae) – Cave morph (El Pachón population)

Crustaceans:

  • Typhlatya mitchelli (Atyidae)
  • Macrobrachium cf. acanthochirus (Palaemonidae)
Threats to ecology

Although relatively isolated, the cave ecosystem is vulnerable to groundwater pollution, excessive groundwater extraction, quarrying, land-use changes above the cave, and increasing tourism. Because cave species have evolved in highly stable environments, even small changes in water quality or hydrology can have significant ecological consequences. The conservation of the surrounding karst landscape is essential for protecting this unique subterranean ecosystem.

Riparian zone

Trees near the aquatic habitat
Many - Ficus cotinifolia (Moraceae)
Trees near the aquatic habitat
Many - Lysiloma divaricatum (Fabaceae)
Trees near the aquatic habitat
Few - Bursera simaruba (Burseraceae)

Bibliography

Sitography

→ FishBase
→ Eschmeyer’s Catalog of Fishes
→ Plants of the World Online
→ IUCN Red List
→ Encyclopedia of Life