This pupfish is endemic to El Pandeño, a hot spring in Julimes, Chihuahua, Mexico, and it is adapted to life in water that reaches temperatures as high as 46 °C (114 °F).

[5] Females and young have reticulate patterns of dark and light silver-brownish bands of varying lengths and thickness over the flanks, as well as a conspicuous black spot or ocellus on the distal edge of the dorsal fin.

Mating pairs come together, swimming, swirling and waving their bodies simultaneously as the female releases single eggs which are immediately fertilized by the male.

[5] The Julimes pupfish is considered to be the freshwater teleost that lives in the highest-temperature waters on the planet[5][8] and is possibly also the vertebrate with the smallest known distribution range.

[6] Effective population size was evaluated in 2013 and found to be critically low, indicating that "this pupfish is at genetic risk of extinction through loss of adaptive variance and, potentially, from inbreeding depression."

[10] In accordance with conservation agreements between Pronatura Noreste A. C. and Amigos del Pandeño, A.C. test results are being used for long-term genetic monitoring under the '‘Vital Signs'’ program for the geothermal Julimes springs.

inhabiting the cooler sections of the system, the recently described cochliopid springsnail (Tryonia julimensis[7]); and IUCN (CR) red listed sphaeromatid isopod (Thermosphaeroma macrura[12]).

[6] In January 2013, Amigos del Pandeño restored ~300 square metres (3,200 sq ft) of dried lower marsh habitat with support from Pronatura Noreste.

Since 1998, all water flow from "El Pandeño" has been allocated to 36 farmers grouped in the "San José de Pandos Irrigation Society" (SJPIS).

[15] In May 2011, "Amigos del Pandeño" called for an initial "Vital Signs" planning workshop with the participation of scientists, experts, natural resource managers and specialists from universities, NGOs and the private sector, in order to develop a Science-based Management Plan for the spring system, and to begin to determine baselines to implement a "Vital Signs Monitoring Program".

[6] During the workshop, it was agreed that the purpose of a "Vital Signs Monitoring Program" would be early detection of environmental changes and providing an overview of the ecological consequences thereof in order to determine whether observations may dictate the need for changes in the management of the ecosystem and its natural resources.

[6] On November 30, 2013, an area of 368 ha (909 Acres) comprising a group of springs and irrigation canals, including "El Pandeño" hotspring was nominated Ramsar Site No.