San Marcos River just downstream from Rio Vista Dam, San Marcos, Hays County, Texas (Hubbs and Hubbs in Hubbs and Springer 1957).
Etymology/Derivation of Scientific Name
Maximum size: 44 mm (Page and Burr 1991).
Coloration: Postanal streak prominent (darker than markings on scale pockets); dark markings on mouth; median row of spots on dorsal fin; lateral stripe thin and threadlike; caudal fin with prominent dark markings; markings on side rounded specks; dorsal and (in females) anal fins with yellow pigmentation (lost in preservation; Hubbs et al. 1991). Olive above, dark stripe along back to dorsal fin; iridescent blue and yellow on silver side (Page and Burr 1991).
Counts: Usually 7 dorsal rays (Page and Burr 1991).
External morphology: Terminal hook on 4th and 5th rays of gonopodium angular at tip; tip of anterior branch of 4th ray of male gonopodium extends as far as tip of posterior branch; pectoral fin of males with slight indention, shallower than widest pectoral fin ray; distal hook on 4th ray of gonopodium usually unsegmented; distal segments of anterior branch of 4th fin ray of gonopodium not coalesced to elbow; spines at tip of 3rd anal fin ray of male gonopodium 4-10 times longer than wide; origin of dorsal fin well behind origin of anal fin (Hubbs et al. 1991).
Internal morphology: Intestinal canal short with few convolutions; teeth barely moveable (Hubbs et al. 1991).
Distribution (Native and Introduced)
Texas distribution: Range originally restricted to headwaters of San Marcos and Comal rivers in central Texas; introduced into a number of other drainages, including headwaters of the Concho River (Tom Green County), San Solomon Springs and associated irrigation network (Reeves County), Leon Creek (Pecos County), and Independence Creek (Terrell County; Hubbs et al. 1991). Warren et al. (2000) list the following drainage units for distribution of Gambusia geiseri in the state: Colorado River, San Antonio Bay (including minor coastal drainages west of mouth of Colorado River to mouth of Nueces River).
Abundance/Conservation status (Federal, State, NGO)
Populations in the southern United States are currently stable (Warren et al. 2000). Species is highly localized and uncommon (Page and Burr 1991).
Macrohabitat: Large springs (Page and Burr 1991).
Mesohabitat: Prefers moving, but not turbulent, water away from stream banks (Hubbs and Peden 1969; Stevens 1977). Found only in cold, clear, high-volume discharge springs near emergence from underground limestone aquifers; Gambusia geiseri often far outnumbers the mosquitofish (G. affinis) where the two species occur together (Harrell 1980). During May sampling in the cienega of Balmorhea State Park, Texas, many young were found associated with bullrushes (Edwards 1999). According to Hubbs (2001), species is apparently negatively influenced by flooding.
Spawning season: Due to physically constant habitat, may spawn year-round; in Devil’s River, Texas, gravid females dominate populations from late March to early June (Harrell 1980). Hubbs (1998) presented data indicating that Gambusia geiseri spawns throughout the year in stenothermal waters, regardless of other environmental factors. At San Marcos Springs, Texas, spawning occurs during all seasons of the year (Stevens 1977). Spawning occurs year-round in the headwaters of the San Marcos River, Texas, with peak in November, and one-third of February females carrying eyed embryos (Davis 1978).
Spawning Behavior: Hubbs and Delco (1960) found Gambusia geiseri males to exhibit very low courtship activity for females of other species (G. affinis, G. heterochir, and G. hurtadoi), and suggested that this behavior may be due to its extensive sympatry with G. affinis in its natural range.
Fecundity: Stevens (1977) noted that fecundity is an increasing function of female body size; the average number of eggs for size class 25-27.5 mm SL is about 8, while the average egg number is about 18 for the size class 35-37.5 mm SL. Variation in size and number of offspring exists among populations (Hubbs 1996; Marsh-Matthews et al. 2005). Marsh-Matthews et al. (2005) reported mean brood size of 16.1 ±6.3 (t= -8.0, n+49, P<0.001), and mean embryo mass of 2.2±0.3 mg dry mass. Interbrood interval ranges from 40-60 days, depending on temperature (Stevens 1977; Hubbs 1996; Marsh-Matthews et al. 2005). Stevens (1977) reported that larger females produced slightly larger offspring, and Dorsey (1990) reported that larger females had larger embryos. Direct experimental evidence of maternal-to-embryo nutrient transfer for this species, one which was previously believed to be solely dependent on nutrients and energy stored in the egg prior to fertilization; finding suggests that matrotrophy may be important maternal investment strategy for Gambusia geiseri (Marsh-Matthews et al. 2001; DeMarais and Oldis 2005; Marsh-Matthews et al. 2005). Hubbs (1999) reported on the effect of light intensity on brood production, noting that Gambusia geiseri had fewer broods at low lux of incandescent light, and the species produced more broods at each increase in light intensity.
Age/size at maturation: Stevens (1977) reported first broods produced by females about 25 mm SL.
Growth and Population structure: Considerable growth may occur between production of a first and second brood by a female: females produced first brood at about 26 mm SL, and second brood at about 33 mm SL. Females over 30 mm SL considered “old”, and those between 20-30 mm SL considered “young” (Stevens 1977). Stevens (1977) reported seasonal variation in sex ratio with the abundance of males relative to females dropping simultaneously during the summer months and rising sharply again in the fall. Females are much larger than males; large females usually pregnant and pot-bellied (Page and Burr 1991).
Phylogeny and morphologically similar fishes:
Gambusia geiseri is similar to the mosquitofish (Gambusia affinis) and the Pecos gambusia (Gambusia nobilis), but the latter two species lack black spots on the side; have black teardrop, black anal spot on female. G. geiseri is sympatric with G. affinis over most of its range (Hubbs and Delco 1960), and with G. nobilis in some parts of its range (Hubbs et al. 1995). G. geiseri is sympatric with G. georgei (San Marcos gambusia; Edwards et al. 2002); G.georgei lacks the following characters of G. geiseri: prominent post-anal streak, spots along sides and obvious dusky markings on lips, and recurved hook on one of the 3rd anal ray spines (Edwards 1999). Other Gambusia species differ from Gambusia geiseri in that they lack row of discrete black spots on caudal fin (Page and Burr 1991). Member of G. nobilis species group (Hubbs and Springer 1957), which occurs in northeastern Mexico and southwestern United States; only member of group with recurved hooks on proximal spines of ray three (male gonopodium; Harrell 1980).
Cestoda (1), Trematoda (2), Nemata (4), Acanthocephala (2; Mayberry et al. 2000).
Commercial or Environmental Importance
In the 1930’s, Gambusia geiseri was distributed throughout west Texas by the Department of Health for mosquito control (Hubbs and Springer 1957). According to Stevens (1977), human disruption of the riverine (San Marcos River, Texas) environment resulted in decreased reproductive activity by G. geiseri.
[Additional literature noting collection of this species from Texas locations includes, but is not limited to the following: Hubbs (1957); Hubbs and Hettler (1958); Conner (1977); Stevens (1977); Devil’s River (Harrell 1978); Leon Creek (Hubbs et al. 1978); Hillebrandt Bayou (Linam and Kleinsasser 1987a); Nolans River (Linam and Kleinsasser 1987b); South Concho River (Fulling 1993); Hubbs et al. (1995); Craig (1996); Linam and Kleinsasser (1996); Winemiller and Anderson (1997).]
Conner, J.V. 1977. Zoogeography of freshwater fishes in western Gulf slope drainages between the Mississippi and the Rio Grande. Ph.D. dissertation. Tulane Universtiy, New Orleans, Louisiana. 280 pp.
Craig, N.E. 1996. Effects of vegetation on population structure of the largespring gambusia, Gambusia geiseri. M.S. Thesis. Angelo State University, San Angelo, Texas.
Davis, J.R. 1978. Reproductive seasons in GAmbusia affinis and Gambusia geiseri (Osteichthyes: Poecilidae) from southcentral Texas. Texas Journal of Science 30(1):97-99.
DeMarais, A., and D. Oldis. 2005. Matrotrophic transfer of fluorescent microspheres in Poeciliid fishes. Copeia 2005(3):632-636.
Dorsey, L. 1990. Variation in size and number of embryos in the largespring gambusia, Gambusia geiseri. Unpublished M.S. thesis, Angelo State University, San Angelo,Texas.
Edwards, R.J. 1999. Ecological profiles for selected stream-dwelling Texas freshwater fishes II. Report to the Texas Water Development Board. 69 pp.
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.
Fulling, G.L. 1993. Variation in population size and structure of the largespring gambusia, Gambusia geiseri, in the headwaters of the South Concho River, Tom Green County, Texas. M.S. Thesis. Angelo State University, San Angelo, Texas.
Harrell, H.L. 1978. Response of the Devil’s River (Texas) fish community to flooding. Copeia 1978(1):60-68.
Harrell, H.L. 1980. Gambusia geiseri (Hubbs and Hubbs), Largespring gambusia. pp. 541 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. 1957. Distributional patterns of Texas fresh-water fishes. The Southwestern Naturalist 2(2/3):89-104.
Hubbs, C. 1996. Geographic variation in life history traits of Gambusia species. In: Proceedings of the Desert Fish Council 1995 Symposium 27:1-21.
Hubbs, C. 1998. Large spring gambusia (Gambusia geiseri) produces young in all seasons. Texas Journal of Science 50(4):343-344.
Hubbs, C. 1999. Effect of light intensity on brood production of livebearers Gambusia spp. Trans. Amer. Fish. Soc. 128:747-750.
Hubbs, C. 2001. Environmental correlates to the abundance of spring-adapted versus stream-adapted fishes. Texas Journal of Science 53(4):299-326.
Hubbs, C., and A.E. Peden. 1969. Gambusia georgei sp. nov. from San Marcos, Texas. Copeia 1969:357-364.
Hubbs, C., and E.A. Delco, Jr. 1960. Preference in males of four species of Gambusiine fishes. Evolution 14(2):145-152.
Hubbs, C., and V.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. Tex. J. Sci. 9:279-327.
Hubbs, C., and W.F. Hettler. 1958. Fluctuations of some central Texas fish populations. The Southwestern Naturalist 3(1/4):13-16.
Hubbs, C., A.F. Echelle, and G. Divine. 1995. Habitat partitioning by two congeners (Gambusia geiseri and Gambusia nobilis) at Balmorhea State Park, Texas. Texas Journal of Science 47(4):325-326.
Hubbs, C., R.J. Edwards, and G.P. Garrett. 1991. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science, Supplement 43(4):1-56.
Hubbs, C., T. Lucier, E. Marsh, G.P. Garrett, R.J. Edwards, and E. Milstead. 1978. Results of an eradication program on the ecological relationships of fishes in Leon Creek, Texas. The Southwestern Naturalist 23(3):487-496.
Linam, G.W., and L.J. Kleinsasser. 1987a. Fisheries use attainability study for Hillebrandt Bayou. River Studies Report No. 1. Resource Protection Division, Texas Parks and Wildlife Department, Austin. 18 pp.
Linam, G.W., and L.J. Kleinsasser. 1987b. Fisheries use attainability study for the Nolands River (River Segment 1227). River Studies Report No. 2. Resource Protection Division, Texas Parks and Wildlife Division, Austin. 13 pp.
Linam, G.W., and L.J. Kleinsasser. 1996. Relationship between fishes and water quality in the Pecos River, Texas. River Studies Report No. 9. Resource Protection Division, Texas Parks and Wildlife Department, Austin. 11 pp.
Marsh-Matthews, E., P. Skeierkowski, and A. DeMarais. 2001. Direct evidence for mother-to-embryo transfer of nutrients in the livebearing fish Gambusia geiseri. Copeia 2001(1):1-6.
Marsh-Matthews, E., M. Brooks, R. Deaton, and H. Tan. 2005. Effects of maternal and embryo characteristics on post-fertilization provisioning in fishes of the genus Gambusia. Oecologia 144(1):12-24.
Mayberry, L.F., A.G. Canaris, J.R. Bristol, and Scott L. Gardner. 2000. Bibliography of parasites and vertebrate host in Arizona, New Mexico and Texas (1893-1984). University of Nebraska Harold W. Manter Laboratory of Parasitology Web Server, published on the World-Wide-Web, 100 pp.
Page, L.M., and B. M. Burr. 1991. A Field Guide to Freshwater Fishes of North America, North of Mexico. Houghton Mifflin Company, Boston, Massachusetts. 432 pp.
Stevens, F.B. 1977. Patterns in the reproductive ecology of Gambusia geiseri. M.A. Thesis. University of Texas at Austin, Austin. 100 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.
Winemiller, K.O., and A.A. Anderson. 1997. Response of endangered desert fish populations to a constructed refuge. Restoration Ecology 5(3):204-213.