 Male  Gravid female Photographs by Richard T. Bryant and Wayne C. Starnes. All rights reserved under applicable copyright law. - Photographs are of the closely related Gambusia affinis |
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| Scientific Name | Specimen Records | |||
| Gambusia holbrooki Girard | ATBI Database | |||
| Common Name | ||||
| Eastern mosquitofish | ||||
| Kingdom | Phylum | Class | Order | Family |
| Animalia | Chordata | Actinopterygii | Cyprinodontiformes | Poeciliidae |
| Animals | Vertebrates | Ray-finned Fishes | Cyprinodontiforms | Livebearers |
Gambusia holbrooki is a small fish (maximum length 1.4-2.5 in.) that has a spotty distribution in shallow waters of swamps and lakes and sluggish backwaters of creeks and rivers in eastern Tennessee, likely as a result of introductions for mosquito control. The other mosquitofish of the area surrounding the Park is G. affinis (Baird and Girard), the western mosquitofish. The two species, formerly considered to be subspecies, are very similar in appearance, differing primarily in number of dorsal and anal fin rays, and in the structure of the gonopodium. Both eastern and western mosquitofish were widely introduced in the first half of the 20th century, and all populations in and near the Park are likely the result of these introductions. Eastern mosquitofish have a dorsally flattened body, upturned mouth, and strong anterior teeth, and are well adapted to surface feeding. They are gray to straw-yellow colored dorsolaterally with large cycloid scales well outlined by dark pigment. The belly is silvery, and is often greatly distended in pregnant females. A black subocular bar is generally present, and the body and caudal fin are often speckled with black. In females, the dark lining of the posterior body cavity often shows through the skin as a large dark spot on either side above the anus.
Eastern mosquitofish spend much of their time cruising about the surface in quiet, shallow backwaters where they feed opportunistically on fallen terrestrial insects and other organisms. When abundant, mosquito larvae become a preferred prey item for these fishes (Hildebrand 1925; Hess and Tarzwell 1942). This fish has only been collected in Chilogatee Branch embayment of Chilhowee Reservoir and in Tab Cat Creek (originally assumed to be G. affinis, but in the absence of voucher specimens, now assumed to be the same species as found in Chilogatee Branch embayment).
SPECIES DESCRIPTION
Size: maximum total length of females 65 mm (2.5 in.); maximum total length of males
35 mm (1.4 in.)
Color: dorsolateral area gray to straw-yellow with scales well outlined with dark pigment;
black subocular bar often present; body and caudal fins often speckled with black
Fins: dorsal fin rays usually 8; anal fin rays 10, and highly modified in males; pectoral
fin rays 12-14; pelvic fin rays 6; principal caudal fin rays 13-16
Lateral-line scales: 30
Gill rakers: 12-14
Similar species: The western mosquitofish, Gambusia affinis is very similar and occurs in several areas near the Park. Gambusia holbrooki has one more ray than G. affinis in both the dorsal and anal fins, in addition to differences in the structure of the male gonopodium (see Etnier and Starnes. 1993).
DISTRIBUTION
North America:
 |
Native range probably was the Atlantic Coastal Plain from the Delaware River drainage south through Florida, and the Gulf Coastal Plain of Florida and perhaps to western Alabama. The similar western mosquitofish had a mostly Coastal Plain distribution throughout the remainder of the Gulf Coastal Plain and up the Mississippi River Embayment to southern Illinois (Wooten et al. 1988; Rauchenberger 1989). Range information given in Jordan and Evermann (1896) indicates that G. affinis was probably more or less restricted to the west Tennessee Coastal Plain at that time; but, it was present in east Tennessee as early as 1920, based on preimpoundment records. Reliability of many records is uncertain, since only G. affinis was thought to occur west of the Florida Panhandle and the Atlantic Slope until very recently. Both mosquitofish have probably expanded their ranges considerably within recent decades, possibly assisted by favorable human-induced habitat alterations. |
In Park:
 Click map to enlarge. |
Gambusia holbrooki has only been collected in the Tab Cat Creek and Chilogatee Branch embayments of Chilhowee Reservoir (Little Tennessee River system). Records from 1968 and 1989 (Simbeck 1990) of G. affinis from the Tab Cat Creek embayment (also Chilhowee Reservoir) likely represent G. holbrooki, but no voucher specimens are available. |
NATURAL HISTORY
The following is based primarily on the very similar G. affinis, but is presumably appropriate for G. holbrooki as well. Reproduction occurs throughout the warmer months; several males may court a female, with one male usually dominant. Internal fertilization is achieved by passage of sperm along a groove in the male gonopodium. Sperm are stored within the female's reproductive system and used to fertilize repeated broods of a few to a hundred or more young. A single female may have three to four broods a year, with young eventually born as well-developed juveniles (Krumholz 1948).
Growth of juveniles is rapid, and individuals born early in a season reach maturity and may reproduce that season; these fish may not survive to the following season. Individuals born late in the season mature and breed the following year. Females grow much more rapidly than males and attain a larger size; males experience high mortality in summer, and are considerably outnumbered by females by late summer. Life span is probably never more than a year for either sex (Hildebrand 1927).
The high parental care afforded by the livebearers, as well as the species' high tolerance of elevated water temperatures, low oxygen, and poor water quality ensure the success of mosquitofish in habitats unsuitable for many other species of fish.
CONSERVATION BIOLOGY
Special Protection Status:
Rangewide: There are no federal or state listings for Gambusia holbrooki in Tennessee.
In Park: Gambusia holbrooki has no special status in the Park. However, all plants and animals are protected in National Parks and collection requires a permit that is usually granted only for scientific or educational purposes.
ACKNOWLEDGEMENTS
Field work:
N/A
Supporting Institutions:
N/A
Text:
David A. Etnier and Elizabeth L. Etnier.
Photographs:
Richard T. Bryant, Atlanta, Georgia and Wayne C. Starnes, Curator of Fishes, North Carolina State Museum, Raleigh, NC. Copyright 2001 by Richard T. Bryant, all rights reserved.
Drawings:
N/A
Maps:
U.S. Map - Etnier, David A. and Wayne C. Starnes. 1993. The Fishes of Tennessee. University of Tennessee Press. Knoxville, Tennessee.
Web Page:
REFERENCES
Etnier, David A. and Wayne C. Starnes. 1993. The Fishes of Tennessee. University of Tennessee Press. Knoxville, Tennessee.
Hess, A. D. and C. M. Tarzwell. 1942. The feeding habits of Gambusia affinis affinis, with special reference to the malaria mosquito, Anopheles quadrimaculatus. Amer. J. Hygeine 35:142-151.
Hildebrand, S. F. 1925. A study of the topminnow Gambusia holbrooki in its relation to mosquito control. U. S. Public Health Serv. Bull. 153.
Hildebrand, S. F. 1927. Sex ratio in Gambusia. Biol. Bull. 53:390-404.
Jordan, D. S. and B. W. Evermann. 1896-1900. The fishes of North and Middle America: a descriptive catalogue of the species of fish-like vertebrates found in the waters of North America, north of the Isthmus of Panama. Bull. U. S. Nat. Mus. 47:1-3313.
Krumholz, L. A. 1948. Reproduction of the western mosquitofish, Gambusia affinis (Baird and Girard), and its use in mosquito control. Ecol. Monogr. 18:1-43.
Rauchenberger, M. 1989. Systematics and biogeography of the genus Gambusia (Cyprinodontiformes, Poeciliidae). Amer. Mus. Novit. 2591.
Simbeck, Damien J. 1990. Distribution of the Fishes of the Great Smoky Mountains National Park. Master of Science Thesis, University of Tennessee.
Wooten, M. C., K. T. Scribner, and M. H. Smith. 1988. Genetic variability and systematics of Gambusia in the southeastern United States. Copeia 1988:283-289.
