Overview
Pecos gambusia are endemic to the Pecos River basin in southeastern New Mexico and western Texas, and originally ranged from near Fort Sumner, New Mexico to the area around Fort Stockton, Texas. At present, the species is restricted to four main areas, two in New Mexico and two in Texas. Populations live in springs, sinkholes, creeks, and ditches in Bitter Lake National Wildlife Refuge, near Roswell, New Mexico; Blue Spring, east of Carlsbad Caverns National Park, New Mexico; the Diamond Y springs and draw (=Leon Creek), near Fort Stockton, Texas; and the San Solomon springs complex near Balmorhea, Texas. Extirpated populations include the Pecos River near Fort Sumner and North Spring River in New Mexico, and Leon and Comanche springs, which are now dry, in Texas.
In the San Solomon springs complex, Pecos gambusia populations number in the hundreds to thousands, with a total abundance across all localities of several thousand to the low tens of thousands, subject to within-year and year-over-year variation. In this area, the population is relatively stable in the large ponds within Balmorhea State Park, while the population in the smaller spring pools and ciénegas outside the park is more tenuous. The total abundance of populations within the Diamond Y Spring Preserve is likely in the thousands, but precarious due to increasing threats and a lack of stable habitat free of significant threats. The total abundance of Pecos gambusia at all sites within Bitter Lake NWR is probably in the tens of thousands, based on studies completed in the 1970s and 1980s and the relative stability of the population there. No research has been conducted on the Blue Spring population since the 1970s, when the population was estimated to number in the hundreds of thousands.
The Pecos gambusia was listed as endangered on October 13, 1970 (35 FR 16047). No critical habitat has been designated for the species. Five-year reviews were completed in 2018 and 2025.
The best available scientific information indicates that the primary threats to Pecos gambusia are: 1) habitat loss and degradation associated with declining spring flows, 2) hybridization or competition with western mosquitofish and/or largespring gambusia, 3) potential contamination of aquatic habitat as a result of local oil and gas development, and 4) for the Diamond Y Preserve, the destruction and degradation of habitat as a result of feral hog activity. The threat of habitat loss and degradation is the most immediate and pressing of the threats.
The Nature Conservancy. 2023. “Monitoring and Habitat Enhancement at Diamond Y Spring Preserve (TX).” The Nature Conservancy.
U.S. Fish and Wildlife Service. 1983. “Pecos Gambusia Recovery Plan.” Albuquerque, New Mexico: U.S. Fish and Wildlife Service.
———. 2018. “Pecos Gambusia (Gambusia nobilis) 5-Year Review: Summary and Evaluation.” Austin, Texas: U.S. Fish and Wildlife Service.
———. 2025. “Pecos Gambusia (Gambusia nobilis) 5-Year Review: Summary and Evaluation.” Austin, Texas: U.S. Fish and Wildlife Service.
Scientific Name
Identification Numbers
Characteristics
Habitat
Pecos gambusia inhabit stenothermal springs, runs, spring-influenced marshes (ciénegas), and irrigation canals carrying spring waters. Some populations are also known from areas with little spring influence; these habitats generally have abundant overhead cover, and include sedge-covered marshes and gypsum sinkholes. One or two other introduced gambusia may be found in association with Pecos gambusia. When they co-occur, the two species will segregate by habitat types, if both are available. For example, Pecos gambusia prefers stenothermal water, while western mosquitofish prefers eurythermal habitats. When Pecos gambusia and largespring gambusia are both present, Pecos gambusia will tend towards areas with more aquatic vegetation and use lower parts of the water column, while largespring gambusia tends to be at the surface or in open water over non-vegetated substrates.
Echelle, Anthony A., and Alice F. Echelle. 1980. “Status of the Pecos Gambusia (Gambusia nobilis).” Albuquerque, NM: U.S. Fish and Wildlife Service.
Hubbs, Carl L., A.F. Echelle, and G. Divine. 1995. “Habitat Partitioning by Two Congeners (Gambusia geiseri and Gambusia nobilis) at Balmorhea State Park, Texas.” The Texas Journal of Science 47: 325–326.
———. 2001. “Environmental Correlates to the Abundance of Spring-Adapted versus Stream-Adapted Fishes.” Texas Journal of Science 53 (4): 299–326.
———. 2003. “Spring-Endemic Gambusia of the Chihuahuan Desert.” In Aquatic Fauna of the Northern Chihuahuan Desert, Contributed Papers from a Special Session, 46:127–133. Alpine, Texas: Museum of Texas Tech University. Accessed from https://www.desertfishes.org/dfc/proceed/2001/Chih_desert_symp/09AFNCD%….
U.S. Fish and Wildlife Service. 1983. “Pecos Gambusia Recovery Plan.” Albuquerque, New Mexico: U.S. Fish and Wildlife Service.
Food
Pecos gambusia feed relatively non-selectively, consuming a diversity of food types, including amphipods, filamentous algae, ostracods, protozoa, detritus, invertebrate eggs, and diatoms.
Hubbs, Clark, Thomas Lucier, Edie Marsh, Gary P. Garrett, Robert J. Edwards, and Elisabeth Milstead. 1978. “Results of an Eradication Program on the Ecological Relationships of Fishes in Leon Creek, Texas.” The Southwestern Naturalist 23 (3): 487–496. https://doi.org/10.2307/3670255.
Winemiller, Kirk O., and Allison A. Anderson. 1997. “Response of Endangered Desert Fish Populations to a Constructed Refuge.” Restoration Ecology 5 (3): 204–213. https://doi.org/10.1046/j.1526-100X.1997.09725.x.
Physical Characteristics
Baird and Girard described Pecos gambusia based on material from Leon and Comanche springs, Pecos County, Texas. Leon Springs was later designated the type locality. Pecos gambusia are small, live-bearing Cyprinodontiform fish in the family Poeciliidae. Individuals of this species are generally light reddish-brown in color with a somewhat paler underside. Male Pecos gambusia are usually 32 millimeters (mm [1.26 inches (in)]) or less in total length, while females may exceed 60 mm (2.36 in). Pecos gambusia are relatively robust for a gambusia, with an arched back and a caudal peduncle depth that is approximately two-thirds of the head length. The margins of the scale pockets are outlined in black and spots are normally absent on the caudal fin; however, sometimes a faint medial row of spots may be present. Females have a prominent black area on the abdomen that surrounds the anus and anal fin. The male gonopodium has a number of unique features, which can be used to distinguish Pecos gambusia from other gambusia species.
Baird, S.F., and C. Girard. 1853. “Description of New Species of Fishes Collected by Mr. John H. Clark, on the U.S. and Mexican Boundary Survey, under Lt. Col. Jas. D. Graham.” Proceedings of Academy Natural Science Philidelphia 6: 387–390.
Bednarz, James C. 1975. “A Study of the Pecos Gambusia.” Santa Fe, New Mexico: New Mexico Department of Game and Fish.
Echelle, Alice F., and Anthony A. Echelle. 1986. “Geographic Variation in Morphology of a Spring-Dwelling Desert Fish, Gambusia nobilis (Poeciliidae).” The Southwestern Naturalist 31 (4): 459–468. https://doi.org/10.2307/3671700.
Hubbs, Clark, R.J. Edwards, and G.P. Garrett. 2002. “Threatened Fishes of the World: Gambusia nobilis Baird & Girard, 1853 (Poeciliidae).” Environmental Biology of Fishes 64 (4): 428–428. https://doi.org/10.1023/A:1016154429254.
Hubbs, Clark, and Victor G. Springer. 1957. “A Revision of the Gambusia nobilis Species Group, with Descriptions of Three New Species, and Notes on Their Variation, Ecology, and Evolution.” Texas Journal of Science 9: 279–327.
Koster, William J. 1957. Guide to the Fishes of New Mexico. University of New Mexico Press. Accessed from http://archive.org/details/guidetofishesofn0000will.
Propst, David L. 1999. “Threatened and Endangered Fishes of New Mexico.” Santa Fe, New Mexico: New Mexico Department of Game and Fish.
Life Cycle
Data on survival rates for this species in the wild are unavailable, but findings from a study of Pecos gambusia at Bitter Lake National Wildlife Refuge (NWR) led authors to conclude that females live at least three years and are reproductive in the first summer following their birth. Male longevity has not been published, but based on other gambusia species, is likely shorter than that of females, probably extending about one year.
Swenton, Daniella M., and Astrid Kodric-Brown. 2012. “Habitat and Life History Differences between Two Species of Gambusia.” Environmental Biology of Fishes 94 (4): 669–680. https://doi.org/10.1007/s10641-011-9973-1.
Vargas, M. J., and A. de Sostoa. 1996. “Life History of Gambusia Holbrooki (Pisces, Poeciliidae) in the Ebro Delta (NE Iberian Peninsula).” Hydrobiologia 341 (3): 215–224. https://doi.org/10.1007/BF00014686.
Pecos gambusia produce live young, and average from one to four broods during the April through August breeding season. The interbrood interval averages 52 days. The number of embryos is correlated positively with female body size. Over the course of the breeding season, females shift from producing many small embryos to fewer, larger offspring.
Where suitable habitats exist, Pecos gambusia populations can be dense. Because females may have multiple broods of many young in a single season, growth may be explosive when conditions are right. However, due to the short lifespan of the species, population crashes are also possible. Seasonal variation may be extreme, with populations highest at the end of summer and lowest at the end of winter.
Bednarz, James C. 1979. “Ecology and Status of the Pecos Gambusia, Gambusia nobilis (Poeciliidae), in New Mexico.” The Southwestern Naturalist 24 (2): 311–322. https://doi.org/10.2307/3670929.
Hopkins, Alyssa, and Astrid Kodric-Brown. 2015. “Life History of Gambusia nobilis (Pecos Gambusia) from Bitter Lake National Wildlife Refuge.” Environmental Biology of Fishes 98 (7): 1833–1844. https://doi.org/10.1007/s10641-015-0401-9.
Hubbs, Clark. 1996. “Geographic Variation in Life History Traits of Gambusia Species.” In Proceedings of the Desert Fishes Council, 1–21. Accessed from https://www.desertfishes.org/proceedings/DFC_Vol_XXVII.pdf.
Swenton, Daniella M., and Astrid Kodric-Brown. 2012. “Habitat and Life History Differences between Two Species of Gambusia.” Environmental Biology of Fishes 94 (4): 669–680. https://doi.org/10.1007/s10641-011-9973-1.
Geography
Pecos gambusia are endemic to the Pecos River basin in southeastern New Mexico and western Texas, and originally ranged from near Fort Sumner, New Mexico to the area around Fort Stockton, Texas. At present, the species is restricted to four main areas, two in New Mexico and two in Texas. Populations live in springs, sinkholes, creeks, and ditches in Bitter Lake National Wildlife Refuge, near Roswell, New Mexico; Blue Spring, east of Carlsbad Caverns National Park, New Mexico; the Diamond Y springs and draw (=Leon Creek), near Fort Stockton, Texas; and the San Solomon springs complex near Balmorhea, Texas.
U.S. Fish and Wildlife Service. 1983. “Pecos Gambusia Recovery Plan.” Albuquerque, New Mexico: U.S. Fish and Wildlife Service.
———. 2025. “Pecos Gambusia (Gambusia nobilis) 5-Year Review: Summary and Evaluation.” Austin, Texas: U.S. Fish and Wildlife Service.
Timeline
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