Gila topminnow

The Gila topminnow (Poeciliopsis occidentalis) is a small (25-50 mm) guppy-like fish native to the greater Gila River watershed in Arizona, New Mexico, and northern Sonora, Mexico. They prefer smaller creeks and streams with pools and eddies for shelter. Topminnow are unique in that they bear live young rather than lay eggs. In southern Arizona, the topminnow is native to the Santa Cruz and San Pedro River watersheds, however they now only occur in a few specific locations in Pima County, including Cienega Creek, Sabino Canyon, and the lower Santa Cruz River.

Female (left) and male (right) Gila topminnow (photo by Bruce Taubert, AZGFD).

The Gila topminnow was listed as endangered under the Endangered Species Act in 1967 by the U.S. Fish and Wildlife Service due to the loss of habitat and the presence of non-native fish. Changing land use and increased groundwater pumping within the topminnow’s range reduced or eliminated perennial creeks and rivers, leading to drastic loss of available habitat. Pima County acquired the Cienega Creek Natural Preserve in 1986 to protect the existing perennial stream flow for the creek, thereby preserving habitat for the topminnow and other native aquatic species. Additionally, in 2013, Pima County significantly invested in upgrading the quality of the two wastewater treatment facilities that supply the Santa Cruz River with treated effluent, thereby greatly increasing the water quality in this section of the river with the hopes of allowing native fish to return. In November 2017, the topminnow was rediscovered in the lower Santa Cruz near Tucson, where it had been absent for 75 years due to the loss of perennial water flow. Lastly, the County has a begun an outreach campaign to promote the use of topminnow for mosquito control, rather than the non-native and highly invasive mosquitofish (Gambusia affinis).

Pima County partners with multiple groups to monitor Gila topminnow on County conservation lands. These include the Arizona Game and Fish Department for the vector control program and any future reintroductions, Pima Association of Governments (PAG) through quarterly monitoring on Cienega Creek, and the Sonoran Institute through the Living River Program on the lower Santa Cruz.

Gila topminnow in Cienega Creek Natural Preserve (photo by Brian Powell, Pima Co.)

Under Development

U.S. Fish and Wildlife Service - Gila topminnow species page
Sonoran Institute - Living River Program