Livebearers Unlimited: Preserving Xiphophorus couchianus in the Home Aquarium, Part 1: Sad History and Unanswered Questions

Author: Ted Coletti, PhD

One little livebearer that has done much to raise awareness of the need to catalog and conserve endangered fishes is the Monterrey platy Xiphophorus couchianus. Hailing from Mexico, it is fair to say that this little livebearer’s perennial popularity and sought-after status is definitely not due to its flashy appearance. Indeed, Xiphophorus couchianus may be the most “plain Jane” of all the platies and swortails. But the fact that the main population has been extinct since the 1960s, and that a color morph population (possibly a different species or hybrid) may be extinct or at best critically endangered, brings with it the cache of something rare and different.

It also places responsibility. In 2006–2007 Xiphophorus couchianus was selected as the “target fish” for the American Livebearer Association’s revamped Species Maintenance Program (SMP), under the leadership of SMP Chairman Tom Crane of New Jersey. A few populations were distributed to veteran hobbyists, who found them challenging to keep long-term. I have kept the species off and on over the years and find them fascinating in behavior (if not in appearance). Combined with reports from other hobbyists, let’s see if we can provide an overview that will encourage some of you to acquire and successfully maintain this extinct-in-nature animal. But first, some history is needed—and it is a sad history indeed.

Northern Platyfish

Fish of the genus Xiphophorus are commonly referred to as the platies and swordtails. They have been in the tropical fish hobby for as long as it has existed. The three species of Xiphophorus that are known from the Rio Grande drainage in Mexico and are the most northern of the genus are meyeri, gordoni, and couchianus. All of them have extremely limited distributions.

History and Appearance

X. couchianus was described by the American zoologist Charles Girard in 1859. It was actually the second Xiphophorus to be described (after X. helleri) and was named in honor of its discoverer, Major General D. N. Couch. The body color is brownish, with a white belly area. The fins are colorless. The body is slightly elongated, not quite as much as the related X. variatus, but longer than the pervasive X. maculatus from the south. Males and females are usually the same in appearance, albeit with a thinner male. Females can exhibit a pronounced gravid spot and are easy to spot when near labor.

Genders

The gender of the Monterrey platy is determined by a standard XX or XY combination, unlike many other Xiphophorus whose sex determination is controlled either by a complex combination of genes (e.g., X. helleri swordtails), or by a third sex chromosome, “Y,” resulting in different kinds of boys and girls (e.g., X. maculatus platies).

It may surprise some hobbyists to find that alpha-male Monterrey platies with higher, yellow dorsal fins can arise. I’ve only seen them in populations at the New York Aquarium in Coney Island, and in personal shipments from a stock center. This rare sport has eluded me in all my various breeding experiments with the species over the years.

Effects of Pollution

Contrary to popular belief, the Monterrey platy was once more widespread than just Huasteca Canyon. It inhabited springs, streams, ponds, and rivers in heavily vegetated zones that are now dry and part of the metropolis of Monterrey, in Nuevo LeÓn. The type location was probably a spring pool at Cadereyta. Excessive pumping of groundwater for the growing population of Monterrey, as well as pollution, isolated the species to a spring in Huasteca Canyon, where it swam its last lap around 1964.

Hobbyist Info

Dr. Myron Gordon, the famed geneticist and Xiphophorus hunter, collected this fish on several occasions from 1930 through the 1950s. The last population in the hobby was collected in 1961 in the canyon. The current population may be a blend of these various collections and is currently being maintained by the Xiphophorus Genetic Stock Center (XGSC) at Texas State University, in San Marcos, Texas.

Still, continued problems maintaining the species has resulted in the current XGSC stock being descendants of 1992 and 1993 strains from outside sources, which originally came from the 1961 collection. The XGSC staff claim the genetic diversity of the hobby and scientific stock is extremely narrow and, at most, homozygous. It is fortunate that Xiphophorus, unlike other Poeciliids, are famed for their ability to line breed for generations.

Apodaca Population

In 1983, a population of platyfish was discovered from waters in Apodaca, the center of Monterrey. It was listed as “critically endangerd” in 1996, with only a few hundred members of the population restricted to Ojo de Agua de Apodaca. In a paper in 2006 reviewing the Xiphophorus genus, Drs. Klaus Kallman and Steven Kazianis claim that urban sprawl has engulfed the area, and that this population, too, has become lost either from spring failure, pollution, and/or hybridization with other swordtails and platies (wild or hybrids). In recent times there were probably other species of Northern Xiphophorus in the Apodaca area that were lost before being discovered.

Kallman and Kazianis also point out that Xiphophorus couchianus from Huasteca Canyon does not resemble the Apodaca form. The Apodaca population exhibits “deep-lying” large melanophore spotting. X. meyeri, which was also found in the area and is closely related, exhibits similar large melanophore spotting on its flanks. Dr. Myron Gordon, who collected X. couchianus from 1930 through the 1950s, did not mention any specimens with black blotches. Kallman also studied these fish in 1960 and 1961 from the Huasteca Canyon, and in its Rio St. Catarina outflow, and also observed or collected only unspotted specimens.

While the possibility of a spotted version of X. couchianus “cannot be rejected” according to the authors, one can speculate that the Apodaca population may be a hybrid with X. meyeri and/or introduced hobby strains of platies and swordtails, whose unfortunate placement has been reported. A collection from the Apodaca population is being maintained by the Universidad AutÓnoma de Nuevo LeÓn.

Interesting but Problematic

Now that we have attempted to sort out the history and natural status of this beloved Monterrey platy, we can move on to discuss the behavior of this animal. Looks can be deceiving here. True enjoyment of Xiphophorus couchianus is veiled by its visual blandness, and it is not just the satisfaction of preserving an extinct species.

More importantly, we will also review the long-term husbandry and breeding of this extinct livebearer. But why is this species so difficult to maintain long-term, even for seasoned professionals? All these discussions will have to wait until next month, as your columnist will be polling the breeders, public aquariums, and stock centers for their insights, and combining them with his own. Common threads of observations and solutions will be presented. Species maintenance is critical to the continued survival of Xiphophorus couchianus, as it can never be reintroduced to its now-arid habitat.

It is about time the hobby had some consistent and solid answers. Stay tuned…

Guppy Corner

Most of us who frequent pet shops are now treated to a wide range of beautiful guppies. This is in stark contrast to the 1990s, when retail stocks were terrible due to a combination of guppy disease, over-medication and hormones, and poor breeding and transport practices. Although healthier today, I find pet-shop guppy stocks to be dominated by multi-colors (AOC), pale yellows or blues, and orange/reds. Many are quite nice, albeit shorter-finned than show guppies.

Go to a guppy show and you are treated to a wider variety of strains. For me, the most startling are the deep iridescent blues and greens, surprising purples, and creamy pastel yellows. This month we will discuss raising the greens.

Green guppies are challenging fish for breeders, as their colors can change from green to blue to silvery based on condition and lighting. Your first step is, of course, to obtain show-quality strains from a reliable breeder. Hatcheries and auctions sites online are a good start, but I would recommend going to a local guppy auction to avoid the cost and stress of shipping. Alternatively, a visit to the International Fancy Guppy Association (IFGA) website (ww.ifga.org) may help you find a local breeder who will sell to you independently.

After you acquire good stock, the real work begins. Guppies don’t breed true, and you will want your investment to keep looking good after many generations. You also want to make sure your green is consistent and reliable under most settings.

IFGA champions Frank Orteca and Jim Gourlie feel that crossing green guppies with purples is a key to developing a quality green guppy. When crossed with purples, green guppies can acquire more color intensity, increased size, and most importantly, the necessary iridescenceto their color. “There have been many good greens that did not do well on the show bench because their color was flat,” explained the champions.

Of course, after repeated inbreeding, you will get some purple guppies too in your green breeding tanks. Also, the results of this cross will vary depending on the “shade” and “texture” of purple guppy you use for your cross (e.g. dark purple, lavender, pastel).

See the full article on TFH Digital http://www.tfhdigital.com/tfh/200712/#pg44