GILA TOPMINNOW Poeciliopsis occidentalis occidentalis (Baird & Girard, 1854) 



Order: ATHERINIFORMES Family: POECILIIDAE 



Distinguishing characteristics : Size and appearance of Gambusia affinis but no lateral 

 streak on side, nuptial males jet black, gonopodium long and folded into a closed tube. 



Present distribution : In U.S. known only from a spring area in Santa Cruz County and 

 a spring on the San Carlos Indian Reservation, Arizona. 



Former distribution : Once common in the middle and lower Gila River basin of Arizona 

 and adjacent Sonora, Mexico. 



Status : Seriously threatened with extinction. May be extinct in Mexico . 



Estimated numbers : Local populations are large, but undergo marked seasonal 

 fluctuations . 



Fecundity : Excellent where undisturbed. 



Reasons for decline : Introduction of exotics , especially the competitive predator 

 Gambusia affinis ; habitat destruction . 



Protective measures already taken : Present owner of Monkey Spring is sympathetic with 

 need to protect this species . The San Carlos Apache tribal officials are interested in 

 the preservation of this subspecies . 



Measures proposed : Set aside spring habitat on W . W . Kolbe Ranch (near Sonoita) as 

 wildlife monument. 



Number in captivity : 40 to 200 at Arizona State University, Tempe. 



Culture potential in captivity : Not good in indoor aquaria; good in outdoor ponds . 



Remarks : The original distribution of this species in the Gila River basin of Arizona 

 has been drastically curtailed since 1926 by destruction of habitat, drying up of marshy 

 pools, and introduction of exotics--especially Gambusia affinis . It is the only represen- 

 tative of the genus Poeciliopsis in the United States . This species is represented by 

 P. o. sonoriensis in Mexico . 



References : 



Miller, R. R. 1961. Man and the changing fish fauna of the American Southwest. 



Pap. Mich. Acad. Sci . , Arts, and Letters , No. 46, (1960), p. 365-404. 

 and C. H. Lowe. 1964. An annotated check list of the fishes of 



Arizona. In^: The Vertebrates of Arizona, C. H. Lowe, ed. Univ. Ariz. Press, 



Tucson, p. 133-151. 

 Minckley, W. L. and J . E. Deacon. 1968. Southwestern fishes and the enigma of 



"endangered species." Science, Vol. 159, No. 3822, p. 1424-1432. 



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