I haven’t made it to Quitobaquito (yet), but I have seen the Quitobaquito pupfish twice. I saw it first in a pond at the Kris Eggle Visitor Center at the Organ Pipe Cactus National Monument and a second time at the Cabeza Prieta Wildlife Refuge Visitor Center.
According to https://en.wikipedia.org/wiki/Sonoyta_pupfish, the
Quitobaquito pupfish (Cyprinodon eremus) [also known as the Sonoyta pupfish] is one of the most distinct species in its genus. This pupfish ( Cyprinodon – Genus ) is restricted to the Rio Sonoyta Basin in Sonora, Mexico and south-central Arizona, named the Quitobaquito Springs. The Quitobaquito pupfish is the last remaining major population of fish at the springs. Originally, it was considered to be one of three subspecies of C. macularius, including the nominal desert pupfish (Cyprinodon macularius macularius), and the undescribed Monkey Spring pupfish (Cyprinodon sp.), but it has since been reclassified as a distinct species.[1][2]
Due to habitat changes, predation and/or competition with nonnative fishes, and possible wind drift of harmful chemicals from nearby Sonora, Mexico, the Quitobaquito pupfish population is severely reduced in other areas; however, the population at the Quitobaquito Springs remains stable…Conservation efforts for this species includes maintenance of habitats by keeping them free of nonnative aquatic species, and observing population health frequently.
According to an article in Wildlife Views from August 1995 (available as a pdf at http://www.azgfd.gov/i_e/ee/resources/field_notes/fish/quitobaquito_pupfish.pdf),
This pupfish is included on the Department’s 1988 list Threatened Native Wildlife in Arizona as an endangered species. It is also listed by the U.S. Fish and Wildlife Service as endangered. Reasons for listing include habitat destruction and desiccation (including water table drawdown in Sonora, Mexico) and the potential for poisoning by wind-drifting pesticides.
Because the Quitobquito pupfish is endangered, the additional populations have been started at the visitors centers.
I definitely saw some of the pupfish at the Kris Eggle Visitor Center. I was able to get pretty close to 
that pond and see fish swimming around in there. It was more difficult to see the fish at the Cabeza Prieta Visitor Center. That pond is fenced, and there’s a fairly wide strip of land between the fence and the pond. I couldn’t get close enough to the water to say with 100% certainty that I saw a fish. But I think I did. I feel lucky to even be able to see a pond these pupfish are living in.
The aforementioned Wikipedia page says,
This is a photo of a photo of Quitobaquito pupfish on an informational board, not a photo of actual Quitobaquito pupfish.
The Quitobaquito pupfish has a thick, chubby body with a superior mouth filled with tricuspid teeth. The scales have spine-like projections. The body colors of males and females vary. Females (and juveniles) have narrow, vertical dark bands on the sides of the body, with a disjoined lateral band. Although females (and juveniles) have silver bodies, the fins are generally colorless, with the exception of an ocellate spot on the dorsal fin, and sometimes, a dark spot on the anal fin. Mature, breeding males, however, have darker fins, attached to a light to sky-blue body. The posterior part of their caudal peduncle (tailside) is yellow or orange, and sometimes, an intense orange-red.[3]
These pupfish can handle various fluctuations of water temperatures as well; including salinity levels three times that of seawater and temperatures exceeding 95 F (35 C).[5]
The Quitobaquito pupfish are omnivores, consuming all types of aquatic insects, crustaceans, and plants.
I’m not a fish fanatic, but I am glad I’ve been able to learn about these rare creatures.