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Saturday, August 31, 2024

Swordtail Guppies, a brief discussion

Some history and a little personal experience over the last 40 years breeding them.


Grey Bunt Zebrinus Lowersword (Y-Ls)

© Alan S. Bias

Permission granted for nonprofit reproduction or duplication of photos and text with proper credit for learning purposes only.  August 31, 2024 

I’ve been keeping and breeding Guppies since I was eight years old ca. 1969.  Prior to this my father kept a few tanks of near wild-type.  Including a tank in front of my high chair as an infant.  Around 1982 my involvement with the International Fancy Guppy Association (IGFA), along with the breeding and showing of pedigree Guppies began. 

After several years of dabbling around with various Delta strains in 90 tanks, I became intrigued with the world of Swordtail Guppies after finding most Deltas just too large, short lived and sluggish at maturity.  More importantly, Delta demonstrated a general lack of anterior-posterior autosomal color-pattern which had been selected against in a quest for the long sought after solid-colored Guppy.

I formed a long-lasting friendship with the late Don Sauers, a breeder who dedicated most of his years in the hobby to promoting and showing the Swordtail Guppy.  Don did not maintain a large fishroom in his home at the time.  Guess he saw enough fish working in the pet industry.   Around 40 tanks in total, if memory serves.  Of which, one was a large 80+ gallon homemade plywood tank painted blue with a glass front.  In which me kept various African Cichlids.  Several of the breeding tanks were devoted to his limited interest in Deltas, while the majority housed his beloved Doublewords (Ds), Lowerswords (Ls), and a few Topswords (Ts). 

On my first visit to his home in the early-mid 1980s in Columbus, Ohio he pointed out the fish he wished to keep and handed me a net.  For the next several years, in conjunction with Fred Roll and several others, we would show fish against each other one week, and swap stock the next.  Swordtail Guppies have captivated me ever since with their variety, longevity and hardiness.

In the late 1980's and early 1990’s it became apparent to some of us breeders the rigid restrictions imposed upon Swordtail breeders by International Fancy Guppy Association (IFGA) & International Kuratorium Guppy High-breeding (IKGH) well defined show standards, as interpreted by essentially Delta judges, for clear caudal, thin tapering dorsal, narrow caudal shape, strict body-caudal ratios, and reduced color were not only outdated, but severely limited potential for the development of new and novel Swordtail phenotypes.

Bias Ls ca. 1988

Swordtail standards around the world were, and still are for the most part, based on a 1960-70's understanding of genetics and a desire to foster solid colored fish.  In the end it limited our understanding of alleles & gene complexes needed to create Swordtails with a free hand as artistic breeders.  By doing so, it curtailed improvement in Swordtail color, pattern & shape not only in North America and Europe, but also around the world. 

At some point, I decided I am not a “show breeder”, but a “pedigree livestock breeder”.  As a result, I should state that I do not, have not and will never breed my Swordtails Guppies strictly in accordance with any fixed set of show standards.   I do not seek to create a breeding show strain within these narrow confines.  Rather a sound pedigree domestic strain which is reproducible over multiple generations.  One that I can in turn regularly show.

My breeding practice is very straight forward and simple.  I keep few records or notes, and rarely refer to them.  Bear in mind, this applies only to my pedigree breedings and not any planned research breedings for later publication.  I am a sight-breeder who practices skilled vision.  Skilled Vision has been loosely defined as a learned practice that allows for recognition and productive results.  Based on powers of observation and acquired knowledge, with far less proficiency in the language of science.  I study genetics not always to make decisions, but to learn how to avoid reinventing the wheel with every generation.

Current Fishroom

I allow the genotype(s) within my breeding population to lead me in pursuit of the best genetic result for all aspects of fecundity, including color-pattern, by imposing sound breeder selection criteria common to all forms of pedigree livestock breeding.  Stated another way, I breed my fish as I once did my pedigree cattle and pedigree sheep, without ever losing sight of wild-type Poecilia reticulata body, shape and form.  During this process I select for upper moderate body size and maximum sustainable caudal-dorsal extension in several forms at maturity.  All the while maintaining longevity and fertility.  I simply show those individuals at maturity, and not before, that fit accordingly into various shows around the world.  Which most do with rigid culling and selection practice.

All Guppies, including Swordtails, are comprised of sex-linked xantho-erythrophore color pigment (if present), over a layer of violet-blue iridophore structural color, on top of a layer of basal level melanophores.   Under which reside crystalline platelets, acting as mirrors, which determine reflective qualities based on stacking (parallel vs. diverse angles).

Variegation (Var) is comprised of collections of large linear and circular dendritic melanophore in close proximity to violet-blue iridophores, forming dense structures in body and finnage.  Var may be static or motile in nature, i.e. mood dependent expression.  Var is part of wild-type counter-gradient camouflage, in ectopic fashion (residing in upper dermal layers).  Known in breeder circles as “Eye-Spots”, they are generally masked by “solid-genotype” found Deltas.  Outcross will disrupt masking to reveal Var in F1 offspring.

All Swordtails, selected for highly reflective qualities, express Variegation (Var), including Eye Spots to varying degrees.  Highly reflective Swordtails, in contrast to many or most Delta and several small tail phenotypes, to include Roundtail & Speartail, are selected against Opaque (Op), i.e. translucent scale.  Op, zygosity dependent, results in muted and dull coloration, in both males and females, by producing diverse angles in crystalline platelets.  OP is an integral part of wild-type counter-gradient camouflage.

In earlier times, ca. 1970-90, few outcrosses were made by Swordtail breeders with existing Delta strains, other than neutral IFGA Green Delta females.  Such breedings did not result in long-term improvement to Swordtail breeding lines.  This, a direct result of outcrossing with homogeneous solid-colored Deltas largely limited to sex-link structural violet-blue iridophore coloration.   In doing so, all or nearly all autosomal color-pattern could be lost in the short-term.   Including reflective qualities.

These breedings simply produced large dead-end hybrids destined for the show bench, which are genetic dead-ends in a pedigree breeding program.  This occurred only after several generations of backcross to parental Sword strains to regain sword shape and extension.  Any perceived positive results in larger size also resulted in corresponding negative results for reduced reflective qualities, loss of sex-link color, and most importantly autosomal color-pattern.  Which constitutes the basis for highly reflective qualities found in Vienna Emerald Green (VEG) Swordtails.

Over the years, I have relied on rigid selection criteria from within my large breeding population to identify and expose unexpressed color-pattern, and limited outcross to near wild-type for infusion of new traits not found in my existing breeding population.  Rather than outcross to Delta strains, followed by backcrossing to parental Sword strains.

As a rule, I find Swordtail genotypes to be rather straight forward in mode of inheritance(s) for swords and specific sex-linked color-pattern.  Co-expressions and crossover events will often mislead the novice breeder into misinterpreting results.  What is often hard for many breeders to comprehend is the concept of sword type, shape, color and extension not always resulting from singular sex-link genes.  Often, they are result of unbreakable linked gene complexes.   Specific composition can result in better or worse shape and coloration via attraction or repulsion of chromatophores.  Such as yellow, comprised of sex-linked xanthophores residing over white leucophores &/or static autosomal Metal Gold (MG) will produce better result than red, comprised of sex-link erythrophores.  While blond (b) with reduced size and numbers of melanophores found in Var produces better shape than grey.  Refinement tends to come from linebred females, and to a lesser degree males, via positive autosomal concentration.  Whereas detrimental result in shape, color and extension tends to arise from negative disruption via outcross.

Swordtail modes of inheritance can generally be described as follows:

Lowersword (Ls) mode of inheritance is traditionally Y-linked for swords and much basic color-pattern, with a neutral "X" for caudal shape and additional male sex-limited color-pattern expression.  Periodic crossover to X-Ls is common.  Resulting in Lowerswords comprised of Y-Ls, X-Ls and even XY-Ls in co-expression.  I should note that stand-alone X-Ls rarely produce show quality results.

Lowersword (Y-Ls / X-Ls)

Lowersword (Y-Ls)


Topsword (Ts) traditionally fall into two modes of inheritance.  Those expressing Snakeskin Body and Tail (SSb/t) are found in a linked complex of X-Ts, SSb/t.  Those lacking SSb/t are generally Y-linked.  Though, crossover is periodically seen.

Topsword (X-Ts)


Topsword (Y-Ts)

Doubleswords (Ds) mode of inheritance is more complex.  Those expressing Snakeskin Body and Tail (SSb/t) are found in a linked complex of X-Ts, SSb/t.  Those lacking SSb/t are generally X- or Y-linked Vienna or Multi type with periodic crossover.  As such, many are a co-expression of XY-Ds.  Ds are often found in co-expression with X-Ls or Y-Ls  or X-Ts or Y-Ts.  In such true multi-gene Ds phenotypes at various stages of growth mismatched shape, size and extension are common between the upper and lower ray extensions.

Doublesword (Y-O / X-Ds)

Doublesword (Y-Ls / X-Ds)

There are several known linked complexes for Ds and color that pass as a single mode of inheritance.  To include:  Asian X-red, Ds and Asian X-yel, Ds.  Both of which can be combined in co-expression with Y-Ls, or Y-Ds, or Y-Ts.  Though, best results are often achieved with neutral Y-O males used as sires.

Doublesword (Y-Ls / Asian X-red, Ds)
Doublesword (Y-Ls / Asian X-yel, Ds)



Some Ds are simply true phenotypes.  Being solely comprised of Ls and Ts in co-expression, i.e. they are a  non-genetic Ds expression.

Doublesword (Y-Ls / X-Ts)

Differences in expressions between X- &/or Y-link Ls, Ds, Ts produced by crossover events results in peculiarities that breeders can sometimes recognize with experience and enough breedings.  However, most examples of crossover in Ls, Ds, Ts often go unseen by breeders unless regular reciprocal breedings or outcrossing’s are made.

Unfortunately, show standards and the decisions of the powers to be are not always conducive to the best results in pedigree Swordtail breeding.  How a breeder decides to select for traits is a personal decision that should be based on long-term goals, sound practice and ethical considerations for breed attributes.  Breed attributes in this case, should adhere to wild-type Poecilia reticulata body, shape and form.  Otherwise, you run the risk of compromising structural fecundity.

For a pedigree breeding program to succeed long-term your goals should be generally established well before you make the first breeding.  Otherwise, you run the risk of wandering aimlessly.  During which time your breeding population may crash from lack of direction.  Yet, at times you may find need to deviate on occasion to circumvent unforeseen results.  That is part of being a pedigree breeder.  Always make as many breedings as possible and maintain as large a potential breeding population as possible.  In this manner you can make benefit of Mother Nature’s gift to pedigree breeders.  That being the frequent mutations via segregation and recombination during meiosis that occur each generation.  At all times, if and when deleterious alleles are revealed select against them severely to purge from the breeding population.  Do not routinely rely on outcrossing to mask them…


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Long-term selection and attention to detail can reward a breeder not only with positive results, but novel phenotypes not yet introduced into Pedigree Guppy breedings.  Share them with friends as they can just as quickly disappear...

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