Photographer: Chad Thomas Source: nas.er.usgs.gov Public Domain
The largespring gambusia (Gambusia geiseri) is in the class Actinopterygii described as the "ray finned" fishes that are commonly 2.5 cm in length, but males can be up to 4.4 cm. Body color is yellow with darker segments and scales. Adults have dark markings around the mouth and caudal fin. Prominent post anal markings are usually present and blue.
The largespring gambusia is an aggressive fish that outcompetes endangered fish such as the Pecos gambusia (Gambusia nobilis) found in habitats that the invasive largespring gambusia was introduced to. Other naturally occurring fish species may also be at risk by the largspring gambusia. The largespring gambuisa is sympatric with the mosquitofish (Gambusia affinis) and the endandgered Pecos gambusia (Gambusia nobilis), creating the possibility of hybrid species which would put the Pecos gambusia at a greater risk of extinction.
Largespring gambusia have been observed to spawn year round even during unfavorable environmental conditions. This species has an usually high reproductive potential because females are capable of producing a high number of eggs. The average number of eggs carried for the size category 2.5-2.7 cm is 8 eggs, while the largespring gambusia is able to carry 16 eggs (average size female). Females have their first brood when they are 2.5 mm long, followed by the second brood when they are 3.0 mm.
In the 1930's largespring gambusia were introduced to other areas of Texas the for purposes of conservation prior to the knowledge of the aggressive nature towards other native fish species. Records of introduction to other locations indicate reasons of aesthetic purposes for stocking local ponds and streams.
San Marcos and Guadalupe River systems (central Texas)
U.S. Habitat: The largespring gambusia is a non migratory fresh water fish that can be found in the benthopelagic region of large streams.
U.S. Present: Texas
Texas: Diamond Y Creek (Pecos Co), Balmorhea Spring complex, Giffin, East and West Sandia, Phantom Cave springs (Reeves Co), Lazy Pond, Chandler Springs (Terrel Co), headwaters of the Concho River (Tom Green Co), and Comanche Springs (Reeves County)
Largespring gambusia are similar to the mosquitofish (Gambusia affinis) and the Pecos gambusia (Gambusia nobilis), but the largespring gambusia can be differentiated by black spots along the sides.
Contact local parks and wildlife authorities if a suspected largespring gambusia is identified outside of it's native habitat in the San Marcos and Guadalupe River systems.
Hendrickson, D. A., and J. E. Brooks. 1991. Transplanting short-lived fishes in North American deserts: review, assessment, and recommendations. Pages 283-298 in W. L. Minckley and J. E. Deacon, editors. Battle against extinction: native fish management in the American West. University of Arizona Press, Tucson, AZ.
Hubbs, C. 1957. Distributional patterns of Texas fresh-water fishes. The Southwestern Naturalist 2(2/3):89-104.
Hubbs, C. 1998. Large spring gambusia (Gambusia geiseri) produces young in all seasons. Texas Journal of Science 50(4):343-344.
Hubbs, C., R. J. Edwards, and G. P. Garrett. 1991. An annotated checklist of freshwater fishes of Texas, with key to identification of species. Texas Journal of Science, Supplement 43(4):1-56.
Edwards, R.J., C. Hubbs, and G.P. Garrett. 2002. Threatened fishes of the world: Gambusia georgei Hubbs and Peden, 1969 (Poeciliidae). Environmental Biology of Fishes 65:358.
U.S. Fish and Wildlife Service. 1982. Pecos gambusia (Gambusia nobilis) recovery plan. U.S. Fish and Wildlife Service, Albuquerque, NM. iii + 41 pp.