Overview
Big Bend gambusia are only known from the warm spring fed pools and ciénegas near Boquillas Canyon and the Rio Grande in what is now Big Bend National Park in Texas. Habitat modification was extensive before the area became a National Park, and included actions to drain wetlands, practice agriculture, and redirect spring flows, such that the historical habitat is completely absent from the current landscape. At present, the species is restricted to two single-species ponds, a ditch-like pond below Spring 4, and a large Beaver Pond adjacent to the campground and nature trail. Up to 10,000 individuals are estimated to occur across the four ponds in the wild, with the vast majority of Big Bend gambusia living in the two single-species ponds. The population in the Beaver Pond is more precarious, with fewer individuals found there during sampling. The species is also kept in captivity at the Uvalde National Fish Hatchery in Uvalde, Texas, where there are approximately 2000 individuals maintained in outdoor ponds.
The Big Bend gambusia was listed as endangered on March 11, 1967 (32 FR 4001). No critical habitat has been designated for the species. Five-year reviews were completed in 2012 and 2023.
Characteristics
Habitat
Big Bend gambusia inhabit clear, stenothermal, warm spring pools and were historically associated with spring-influenced marshes (ciénegas). They utilize dense aquatic and emergent vegetation as well as open water habitats within these areas, preferring the vegetated areas. The species is currently found in two constructed single-species refuge ponds in Big Bend National Park, but also persists in two other ponds where predatory fishes and western mosquitofish are present.
Hubbs, Clark, Robert J. Edwards, and Gary P. Garrett. 2002. “Threatened Fishes of the World: Gambusia Gaigei Hubbs, 1929 (Poeciliidae).� Environmental Biology of Fishes 65 (1): 82�82.
Rio Grande Fishes Recovery Team. 1984. “Recovery Plan for Big Bend Gambusia.� Accessed from
U.S. Fish and Wildlife Service. 2012. “Big Bend Gambusia (Gambusia gaigei) 5-Year Review Summary and Evaluation.� U.S. Fish and Wildlife Service.
——�. 2023. “Big Bend Gambusia (Gambusia Gaigei) 5-Year Status Review: Summary and Evaluation.� Austin, Texas: U.S. Fish and Wildlife Service. Accessed from
Food
No publications on diet preferences are available, but Pecos gambusia, a similar species in the region, 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.
Winemiller, Kirk O., and Allison A. Anderson. 1997. “Response of Endangered Desert Fish Populations to a Constructed Refuge.� Restoration Ecology 5 (3): 204�213.
Physical Characteristics
Carl Hubbs described Big Bend gambusia based on material from a marshy cattail slough fed by springs at Boquillas, Texas, across the Rio Grande from Boquillas, Mexico. Big Bend gambusia are small, live-bearing Cyprinodontiform fish in the family Poeciliidae. Individuals of this species are generally olive golden with a dark lateral stripe across the body and silvery bellies. Based on collected holotypes, adult males are 17�23 millimeters (mm [0.67�0.91 inches (in)] in standard length, and females are 16�25 mm (0.63�0.98 in) in standard length. Compared to other Gambusia species, Big Bend gambusia are deeper bodied and smaller overall. Females have an anal spot restricted to the anus, and the male gonopodium has a number of distinguishing features that can be used for identification.
Hubbs, Carl L. 1929. “Studies of the Fishes of the Order Cyprinodontes, VIII: Gambusia gaigei, a New Species from the Rio Grande.� Accessed from
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.
Rio Grande Fishes Recovery Team. 1984. “Recovery Plan for Big Bend Gambusia.� Accessed from
Life Cycle
Data on longevity are not available for Big Bend gambusia. A closely related species is the Pecos gambusia; females of that species live at least three years and are reproductive in the first summer following their birth. Big Bend gambusia females probably also quickly reach sexual maturity and live two to three years in the wild. Males likely have shorter lifespans than 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.
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.
Big Bend gambusia produce live young and are thought to have a prolonged reproductive season of at least five months and possible as long as eight months. Fecundity is correlated with female body size and timing, highest in the largest females and peaking in June. The interbrood interval has been estimated at approximately 29 days, making it possible for females to give birth every month, five to eight times per year.
Hubbs, Clark, and Doyle T. Mosier. 1985. “Fecundity of Gambusia Gaigei.� Copeia 1985 (4): 1063�1064. .
Geography
Big Bend gambusia are only known to have occurred in the warm spring fed pools and ciénegas near Boquillas Canyon and the Rio Grande in what is now Big Bend National Park in Texas. At present, the species is restricted to two single-species ponds, a ditch-like pond below Spring 4, and a large Beaver Pond adjacent to the campground and nature trail. The species is also kept in captivity at the Uvalde National Fish Hatchery in Uvalde, Texas, where there are approximately 2000 individuals maintained in outdoor ponds.
Cohen, Adam E. 2025. “Email: ‘How Was Sampling Last Week?’� U.S. Fish and Wildlife Service.
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.
Mallek, Maritza. 2024. “Trip Report � Big Bend National Park, TX: Big Bend Gambusia Site Visit.� Austin, Texas: U.S. Fish and Wildlife Service.
U.S. Fish and Wildlife Service. 2012. “Big Bend Gambusia (Gambusia gaigei) 5-Year Review Summary and Evaluation.� U.S. Fish and Wildlife Service.
——�. 2023. “Big Bend Gambusia (Gambusia gaigei 5-Year Status Review: Summary and Evaluation.� Austin, Texas: U.S. Fish and Wildlife Service. Accessed from
Walker, Scott. 2025. “Email: ‘CSP and BBG Transfer to Ponds at Uvalde NFH.’� U.S. Fish and Wildlife Service.
Timeline
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