Livebearers Unlimited: The Clemenciae Contradiction: Has This Orphan Swordtail Finally Found A Home?

Author: Ted Coletti

When you’re in this hobby long enough, you will eventually experience the “contradictory denizen” of your fishroom. This is a species that is supposedly difficult to breed or maintain, but is successful for you with little effort or skill on your part. For me, it’s diamond tetras and Madagascar lace plants. Sometimes the piscine paradox in question is a so-called “easy one” that continually escapes you, much to your frustration and embarrassment. That’s what kribs and water sprite are for me.


A livebearer that fits this description for many of us is the so-called yellow swordtail, Xiphophorus clemenciae. “So called” because the fish is really more blue than yellow, but “blue swordtail” is already a common name for Xiphophorus alvarezi—a fish that is actually more red than blue! Those who discourage the use of common names for fish will find ammunition here.

The yellow swordtail also possesses two to three red vertical stripes. The “yellow” refers to the sword of X. clemenciae (which is actually more orange than yellow) as well as fins that are slightly tinged in that color. The yellow swordtail is unique in having a pointed snout and dorsal, as well as a fan-shaped caudal (tail) fin. All in all, dominant males are truly lovely fish.

X. clemenciae is a smallish swordtail, reaching only about 2 inches in length (excluding the sword). This is about half the size of a full-grown hobby X. hellerii. However, I have had large specimens thrown occasionally. Males tend to be either early-developing long-sword forms, or late-developing, deeper-bodied, shorter-sword forms. X. clemenciae probably has a standard XX/XY chromosome scheme for sex determination.

Difficult Species?

In the 1980s the yellow swordtail was a much-sought-after fish in Europe. Many hobbyists reported dismal failures keeping it alive, let alone breeding it. The Baensch atlas assigned X. clemenciae a difficulty rating of 4 out of 5.

They evidently forgot to tell this to the Americans, as we found this species generally unproblematic. Richard Pirro of Long Island, New York, has maintained this species for years and observes that a high-protein “meat” component to its diet is an important factor. Livebearer guru Derek Lambert of the UK found success with the European stock when he attempted to replicate the still, clean water conditions he observed in the wild. By contrast, Axelrod and Wischnath earlier proposed “good water flow” and “algae” as part of the diet!

In my June 2006 column, titled “More Than Skin Deep: A Tale of Two Swordtail in the Age of Hybrid Fish,” I demonstrated that even within a species (X. hellerii), there can be pronounced differences in appearance and behavior. Perhaps this helps explain the different experiences with X. clemenciae. There are two yellow swordtail populations circulating in the hobby: “grande” from the Rio Grande in Veracruz, Mexico; and “finca” from the San Carlos type-location in Oaxaca, Mexico.

The X. clemenciae pictured in European hobbyist descriptions and books closely resembles the finca strain. This fish has a short sword and is deep-bodied. The stock that I worked was the grande strain, which looks decidedly different from the finca in being (usually) skinnier and possessing a longer, curved sword. While touchier than other wild swords I have kept, it was not the “mission impossible” species described by some.

Genetic Oddball?

More contradictions follow the yellow swordtail, this time in terms of its origin. Described by Jorge Alvarez in 1959 and named after his wife, X. clemenciae was thought to be a rare, isolated species hailing from the Rio Coatzacoalcos basin in Mexico. DNA comparative studies by Meyer et al. (1994) and Marcus and McCune (1999) challenged the traditional view that the yellow swordtail is part of an evolutionary clade of Southern xiphs that include the common green swordtail X. hellerii, as well as the previously mentioned X. alvarezi. Morphologically, X. clemenciae is easily mistaken for a hellerii-type swordtail. But mitochondrial DNA analyses revealed a surprisingly stronger relationship to the swordless members of the platy clade, and the short-sworded northern swordtail clade. X. clemenciae was indeed an oddball and orphan among xiphs.

That is, until 2004 when acclaimed xiph scientists Klaus Kallman, Ron Walter, Don Morizot, and Steve Kazianis (all affiliated with the Xiphophorus Genetic Stock Center in Texas) found a link between X. clemenciae and two newcomers to the genus: X. mixei and X. monticolus. These scientists proposed that a new, fourth clade of swordtails and platies be erected for these three fish.

These same scientists also happily discovered that, contrary to popular belief and initial collections, the yellow swordtail is fairly widespread and abundant in the Rio Coatzacoalcos Basin uplands, where it replaces the morphologically similar X. hellerii. X. clemenciae can probably be removed from the IUCN Red List of Threatened Species in my opinion.

New Hypothesis

In the past 12 months, a startling new hypothesis has emerged about the mysterious yellow swordtail—that it came about through a natural hybridization of a platy female with an ancestral male swordtail. German scientists Axel Meyer, Wally Salzburger, and Manny Schartl analyzed new nuclear DNA markers and noted the long-standing observation that female xiphs prefer sworded males. They propose that sexual selection through female choice was the likely process in creating the hybrid brood that became X. clemenciae.

Maintaining the Yellow Swordtail

I originally housed two males and three females of the grande strain in a 10-gallon tank aquascaped with rocks and plants. The males fought constantly. The females fought constantly. Eventually only the dominant male and female emerged as viable. The other two females succumbed while the alternate male stayed hiding in the rocks. Seven fry were born from this pair and four survived. Perhaps this trait behavior also helped foster the yellow swordtail’s reputation as a “problem fish.”

Aquarium Requirements

I placed the two adult males in a longer 15-gallon tank with no mechanical filter (just floating plants and rooted vegetation for filtration), and they got along splendidly. I added the four fry (now juveniles) to the mix, and again, no problems. Placing the fish outside for the summer in a 20-gallon high tank accelerated their growth. Their summer resort was replete with driftwood, seashells, Java moss, Java fern, and Vallisneria, with only natural light. All the fish were robust and extroverted, exploring all the regions of the aquarium in peaceful curiosity.

But as soon as one of the juvenile clemenciae showed signs of sexing out female, the fireworks resumed! The dominant male once again subdued the subordinate male and was generally nasty to the other juveniles, especially those developing male traits. This mating-related social behavior is not uncommon in swordtail and variatus Xiphophorus.

Tank Decorating

Attempting a colony of X. clemenciae, I would recommend a tank at least 30 inches long, furnished with various caves and plants to provide hiding places. A very gentle filter, such as an air-powered undergravel or mini power filter set on low, would be appropriate. The use of limestone “tufa” rocks or a little crushed coral would help maintain the calcium-hard water they enjoy. Feed a quality dry food made mixed with freeze-dried meaty foods and Spirulina, and supplement with frozen food, live food, and some occasional parboiled mashed peas (or paste food as described in my November 2006 column, “Revenge of the Paste Foods”).

Thinking About Getting Yellow Swordtails?

The yellow swordtail is an interesting charge, both from a husbandry and ichthyological perspective. It is a beautiful, barred swordtail that would be a welcome addition to the collection of any hobbyist that can provide a dedicated large, aquascaped aquarium.

Dr. Ted Dengler Coletti has been an aquarist and freelance writer for over 20 years. He resides with his patient family, aquariums, and guitars in the New Jersey Skylands, and sits on the Board of the American Livebearer Association. He is a founder of the Northeast Livebearer Association and the Aquarium Hobby Historical Society. Questions, suggestions, or thick, juicy steaks cooked just the way I like ‘em can be forwarded to