Gambusia georgei

San Marcos gambusia






Type Locality

San Marcos River at Hwy. I-35 bridge, Hays County, Texas (Hubbs and Peden 1969).


Etymology/Derivation of Scientific Name







Maximum size: Adult size 25-40 mm SL (Guillory 1980).


Coloration: Dark edges on dorsal and caudal fins; distinctly cross-hatched side; lemon yellow median fins (Page and Burr 1991). No dark bands on sides; median fins without large black spots near their bases (Hubbs et al. 2008).




Body shape: Dorsal fin origin well behind anal fin origin (Hubbs et al. 2008).


External morphology: Distal segments of anterior branch of 4th fin ray of gonopodium coalesced to elbow; spines at tip of 3rd anal fin ray of male gonopodium 4-10 times longer than wide (Hubbs et al. 2008).


Internal morphology: Intestinal canal short with few convolutions (Hubbs et al. 2008).


Distribution (Native and Introduced)

U.S. distribution:


Texas distribution: Restricted to a very limited portion of the San Marcos River springrun several kilometers below the headsprings (Hubbs et al. 2008).


Abundance/Conservation status (Federal, State, NGO)

Extinct (Hubbs et al. 2008); State Endangered (Texas); Federally Endangered; species has always been rare and its existence difficult to document (Hubbs et al. 2008). Listed as Possibly Extinct by the American Fisheries Society; categories of threats: present or threatened destruction, modification, or reduction of habitat or range; and a narrowly restricted range (Jelks et al. 2008). Extinct throughout range (Warren et al. 2000). Species likely extinct (Miller et al. 1989). Live specimens were captured and artificial cultures were established in Austin, Texas (1979) and Dexter, New Mexico (1980); however, these cultures were contaminated by Gambusia affinis, the western mosquitofish, in the early 1980s (Hubbs et al. 2008); the last G. georgei individual captured in the wild was taken in 1981, despite considerable efforts to secure this species since that time. Guillory (1980) noted a decline in G. georgei numbers and the possibility of extinction; in 1969, the population was estimated at less than 1,000, and surveys conducted in 1976 found no specimens.


Habitat Associations



Mesohabitat: Essentially restricted to shallow, quiet, mud-bottomed, shoreline areas without dense vegetation in thermally constant main channel; was common under shaded bridges (Guillory 1980).



Spawning season:


Spawning habitat:


Spawning behavior:




Age at maturation




Growth and Population structure: 




Food habits:


Phylogeny and morphologically similar fishes

Gambusia georgei most distinct Gambusia morphologically and not closely related to any other species (Guillory 1980).


Host Records



Commercial or Environmental Importance




Guillory, V. 1980. Gambusia georgei (Hubbs and Peden), San Marcos gambusia. pp. 540 in D. S. Lee et al., Atlas of North American Freshwater Fishes. N. C. State Mus. Nat. Hist., Raleigh, i-r+854 pp.


Hubbs, C., and A.E. Peden. 1969. Gambusia georgei sp. nov. from San Marcos, Texas. Copeia (2):357-364.


Hubbs, C., R.J. Edwards, and G.P. Garrett. 2008. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science, Supplement, 2nd edition 43(4):1-87.

Jelks, H.L., S.J. Walsh, N.M. Burkhead, S. Contreras-Balderas, E. Diaz-Pardo, D.A. Hendrickson, J. Lyons, N.E. Mandrak, F. McCormick, J.S. Nelson, S.P. Platania, B.A. Porter, C.B. Renaud, J.J. Schmitter-Soto, E.B. Taylor, and M.L. Warren, Jr. 2008. Conservation status of imperiled North American freshwater and diadromous fishes. Fisheries 33(8):372-407.

Miller, R.R., J.D. Williams, and J.E. Williams. 1989. Extinctions of North American fishes during the past century. Fisheries 14(6):22-38.


Page, L. M. & B. M. Burr.  1991.  A field guide to freshwater fishes of North America north of Mexico.  Houghton Mifflin Company, Boston, Massachusetts. 432 pp.


Warren, M.L., Jr., B.M. Burr, S.J. Walsh, H.L. Bart, Jr., R.C. Cashner, D.A. Etnier, B.J. Freeman, B.R. Kuhajda, R.L. Mayden, H.W. Robison, S.T. Ross, and W.C. Starnes. 2000. Diversity, Distribution, and Conservation status of the native freshwater fishes of the southern United States. Fisheries 25(10):7-29.