Poecilia reticulata, McCauley Spring, New Mexico

Photo shows a group of Poecilia reticulata from McCauley Spring, New Mexico

Across the Rio Grande River from Santa Fe, New Mexico are the Jemez Mountains. Nestled in the canyons of these mountains is a warm spring named McCauley Spring.

McCauley Spring feeds a mountain stream about a yard across and maybe 10 inches deep. The crystal clear water emerges at 85°F. The spring’s output first flows into a small manmade pool with a surface area of about 300 square feet. The pool is about three feet deep. From that pool the water cascades into a larger pool about 750 square feet in size and also about three feet deep. Flowing over yet another manmade rock wall, the water rushes down a steep slope into a series of three large spa sized pools each about 5 feet deep. The two upper pools are vegetated with aquatic plants, including Lemna (duckweed) and a plant reminding me of Najas guadalupensis (guppy grass). The spring presently has Poecilia reticulata, the guppy, and Gambusia geiseri, the big spring Gambusia. Neither is native to the spring.

In September 2012, I collected both species, but will write only about P. reticulata at this time. I first saw the guppies in McCauley Spring sometime in 1990. Susie, my wife, and I were visiting the area prior to moving to Santa Fe the next year. We’d picked up some guide books, one of which with a copyright date of 1990 discussed the guppies in McCauley Spring. The guide, as I remember, said the guppies had been there for 75 years. That would have put the guppies introduced into the spring in 1915. That early of an introduction date is unlikely since guppies had only been imported into the US about that time. Unfortunately, I can’t find that particular guide. A probably more reliable reference is a 2001 paper (Ultraviolet Reflectance Patterns of Male Guppies Enhance Their Attractiveness to Females, Astrid Kodric-Brown & Sally C. Johnson, Department of Biology, University of New Mexico) which says, “The Jemez population was introduced into the spring over 30 years ago….” That makes the introduction sometime before 1970. In any event, they’ve been there for quite some time.

Regardless of how long the guppies have been there, they represent an isolated population that probably originated from a handful of fish. Both sexes show very little variation. That’s to be expected of a small, isolated and probably highly inbred population.

In our hatchery we raise this fish just as we do all our livebearers. Six males and about 40-50 females are placed in a 55 gallon breeding vat equipped with an aquaculture netting cage and hornwort (Ceratophyllum demersum) to provide shelter for the fry. After about three months the adults are moved to another vat and the fry are allowed to grow up to be sold. Adults ready to sell are housed in yet another 55 gallon vat. Any losses of breeders are made up from the adult vat when moving the breeders.

The photo shows typical males and females. All the males are very, very similar.