BIG BEND GAMBUSIA Gambusia gaigei (Hubbs, 1929) 



Order: ATHERINIFORMES Family: POECILIIDAE 



Distinguishing characteristics : A tiny gambusia . Color pattern includes much orange 

 and yellow pigments, especially on dorsal and anal fins. Few dark crescent-shaped 

 marks on sides; marks never extend below lower edge of pectoral fin. Eight or nine 

 dorsal fin rays . 



Present distribution : Entire populations are confined to 2 pools in Big Bend National 

 Park , Texas . 



Former distribution : Initially collected in 1928 from Boquillas Spring, Texas. Later, 

 the spring dried up and the type population became extinct. Discovered in 1954 in 

 Graham Ranch Warm Springs. Apparently never widespread. 



Status : In jeopardy . 



Estimated numbers : About 1,000. 



Fecundity : About 20 per brood. 



Reasons for decline : Competition with Gambusia affinis ; reduction in water supply. 

 (Type locality dried up) . 



Protective measures already taken : In 1956, Graham Spring was chemically treated to 

 eliminate G. affinis . Fifteen G. gaigei were transplanted to 3 ponds within the park but 

 none survived. Four specimens were held over the winter at University of Texas, Austin. 

 Two males and 1 female were returned to pools at Graham Ranch area in March 1957. From 

 the 3 survivors the population grew in numbers . G . affinis again infested the pools and 

 threatened the G . gaigei . Live specimens were kept at University of Texas and University 

 of Michigan. When a new pool was developed at Graham Ranch, these specimens were 

 introduced and now the population seems established. Specimens have been planted in 

 Croton Springs within the park to further insure survival of the species . 



Measures proposed : Continued surveillance of habitats to provide protection of water 

 supply and against competition with G . affinis . 



Number in captivity : None . 



Culture potential in captivity : Can be reared successfully in captivity. 



Remarks : The story of the efforts which have been made to insure the survival of this 

 species is unique . At one time the entire population of this species was reduced to 3 

 individuals . Data submitted by the National Park Service . 



References: 



Hubbs , C . L . 1929 . Studies of the fishes of the order Cyprinodontes . VIII . 



Gambusia gaigei , a new species from the Rio Grande. Occas . Pap. Mus . Zool . 



Univ. of Mich., No. 198, lip. 

 Hubbs, C. and H . J. Brodrick . 1963. Current abundance of Gambusia gaigei , 



and endangered fish species. The Southwestern Naturalist, Vol. 8, No. 1, p. 46-48. 



48 



