Hemiray Bifurcation and its effect on swordtail caudal selection...
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Hemiray Bifurcation can quickly be defined as: "A division or fork in the rays of male and female guppy fins."
|Swordtail Female with Hemiray Bifurcation evident|
This is one of those topics that generates very little documentation in the hobbyist world. In the scientific community it is just the opposite and a number of comprehensive studies have resulted in excellent publications. What is not so easily gauged and often overlooked is the effect of Hemiray Bifurcation in a Swordtail strain. The weaknesses it creates and how you should base breeder selections. As Swordtail Guppy breeders, we deal primarily with male finnage as clear &/or roundtail is the norm for females in all but a few strains. From the start we are at a distinct disadvantage vs. broad tail breeders. The simple reason being mother-nature goes against us at every chance. Bifurcation alone creates an ever broadening of the caudal. We start with naturally occurring tail extensions that are very small, thin & short. These having evolved over countless generations with well defined characteristics into rigid gene complexes. Then we attempt to force not only lengthening, but thickening in the process. In the end retain a distinct point while encompassing an increased number of colored hemirays at maturity.
The problem with this desired end result stems from the very nature of the processes involved in the growth of fins. As a rule a guppies finnage including caudal, dorsal, pectoral, anal and pelvic have been regulated by gene complex through the eons to maintain a well defined shape and structure. Fairly smooth edges and round in most fins. Though, points are considered normal as evidenced in the shape of vent fins and small swords in otherwise round caudals. One might say, "Evolution has made it easy for us to keep and breed guppies as long as one stays within the confines it has established."
|Bifurcation and effect on fin edge|
The trouble is few of us as Guppy Breeders have chosen to do so over the last 100 years. Not only do we attempt to force modifications into color & pattern, but also fin shape & extension. For most of us this is limited to a number of established configurations in the caudal and dorsal. Exceptions would include extension genetics involved with long-fin phenotypes variously referred to as; Berlin - Geissen - Ribbon - Swallow. In all instances you will still be forced to make decisions as a breeder based on the influences of Hemiray Bifurcation. At first the process of enlarging a naturally occurring fin type, ie swordtails, seems like it would simply involve traditional breeding techniques with a sufficient number of tanks to let trial and error work its course over a number of generations. After all, we are simply trying to use extension genetics to force more growth into hemirays already part of an occurring tail shape. Or are we?
|Effect of bifurcation on round caudal|
|Type 1 Swordtail|
This is where the bifurcation comes into play. It is the root cause that will lead to a breeder culling many of the Swordtail males produced in both fixed strains and outcross. Most swordtail strains not only include a lengthening, but also an encompass an increased number of rays. To this day the actual genetic makeup of swordtail guppies is still the topic of hot discussion and alot of speculation with breeders around the world. From my experience Swordtails are comprised of two distinct types. Type 1, in general, result from several genes (more likely groups of genes) either individually or in complex to include Elongatus, Aureus, Lineus and Armatus. Producing not only Top & Lower Swords, but also Double Swords as evidenced by those who exhibit an imbalance not only in shape, but also growth between the upper and lower swords. Type 2 is likely the result of the Double Sword gene (Ds) and a lack of Pigmentierte caudalis (Cp).
|Type 2 Swordtail|
As a guppies fins continue to grow each hemiray at a fixed point will split and fork in two. Under normal conditions it will then continue to grow for a fixed length and again fork. This process will continue for as long as each individual fin ray grows. Regardless of shape. Herein, lies first issue we try to circumvent as Swordtail breeders. How do you force a fork into a point? The answer is you cannot. Though, through selection you can create the illusion of a point. In theory this should be pretty easy as we are dealing with a limited total number of hemirays. In practice each is an independent entity with a purpose of it's own. Through a combination of consistent selection for the best tail shape it can be done. But keep in mind you are also trying to load balance your other desired traits for color, shape, size, pattern, growth, maternal, longevity to name but a few. If you concentrate heavily on tail shape then these areas may suffer. It is often necessary to utilize a breeder male that has a weaker point or lessor length. Not only to maintain your established strain, but more often to identify and create additional phenotypes.
|Type 1 Swordtail showing|
about 1/2 of mature length
|Lower Swordtail "pencil tail" |
If you work with Swordtails long enough you will realize that many are more often "camouflaged" Lyretails that have been forced into a swordtail configuration via breeder selection to meet a standard. Why, you ask? It is much easier to create the illusion of a nice clean point from fewer hemirays. I find good swordtail caudal extension contains a larger number of colored & extended rays starting from at rays 3-5, with an increasing number all extending to the final point. The best swords are often composed of a single ray or two forming the entire outside length. Many lines of swordtails to maintain length and clean points have evolved into "pencil tails" with as few as 2-3 total rays showing extension and lacking color on the interior side. Avoiding clear rays on the interior of the swords will help alleviate some issues.
|Lower Swordtail not yet mature|
In contrast many Lyretail's extension start from rays 5-7 with extension in only the next 2-3. Initial Lyretail rays can taper off into those rays that lengthen and extend to the final point, often with those on the interior reversing the process and shortening. A prime example are Schimmelpennig Platinum's. Both pattern and tail shape are closely linked from a complex of Y-link and autosomal traits. It is easily maintained as a true Lyretail and possible to create a Schim. Double Sword. Still most of those offered by breeders for sale or exhibition as Double Swords are frequently Lyres. Examination of which rays form the extension under magnification will confirm this. While the Schim. Lyres have thick rays and stable extensions, the doubles are very prone to splitting and even stray growths. What always perplexed me is why? They reportedly evolved from mutation within Vienna Emerald. As a rule VEG strains have very stable fin type. After 10 years of breeding Schims the only hypothesis I can offer is it results from the combination of Ds and metal in the males.
One of the common problems that arises in a swordtail is fin splitting on the interior portion of a sword, ie the top side of a lower or the under side of a top. This results from weaknesses created where each ray forks. Having put quite a few under magnification, it is rare see a split that happens any distance before a fork. Just at a fork or shortly thereafter is the norm. It is often difficult to distinguish splits resulting from genetic weaknesses and those from environmental issues such as frequent fighting between males. The prior should be frowned upon in breeder selection and preferably culled from a program. While splits resulting from environmental issues will usually heal and continue to grow it is not without consequence on males intended for exhibition. Hemiray growth after an injury, be it natural or surgical, follows a different course from rays unaffected. Not only will the circumference of rays be smaller, the natural segments of each will not be evenly paired with other rays. Additional bifurcation is also reduced if not eliminated in damaged rays. This is often visible in Delta strains in which ragged caudal edges have been surgically altered. The ends of the caudal are clean from new tissue growth surrounding rays that have regrown without forks. Given time new color cells will migrate to the areas of new growth and darken them.
|Lower Sword exhibiting weakness at bifuracations|
For those of your wishing to read further on Hemiray Bifurcation a number of published studies dealing with Zebra Fish are readily available. Two I have found of interest are:
1. Growth Control in the Regenerating Zebrafish Ontogenetic and Fin
Stephen L. Johnson* and Paul Bennettt
2. Position dependence of hemiray morphogenesis during tail fin regeneration in Danio rerio
C. Murciano a, J. Pérez-Claros b, A. Smith c, F. Avaron c, T.D. Fernández a, I. Durán a, J. Ruiz-Sánchez a, F. García a, J. Becerra a, M.-A. Akimenko c, M. Marí-Beffa a,
|Young Vienna Type Double |
Breeding to a defined standard or personal goal is often
what initially attracts us to guppies as a breeder .
Embarking upon a genetic understanding of those fish we choose to cull
and those we decide to retain within a breeding program
often makes the difference in breeder perseverance...