Photo: Female Red Tuxedo Lyretail Swordtail. As is typical of our strain, females don’t have as bright red coloration as males.
We’ve started working on adding three fancy fin types, lyretail, hifin, and plumetail to each of our commercial swordtail, maculatus, and variatus lines. I’m going to use our Red Tuxedo Swords to demonstrate how we do this.
First, let’s describe the three fin types listed above.
Lyretail is dominant allele (variant of a gene) that causes the upper and lower fin rays of the caudal (tail fin) to be elongated. This configuration reminded people of the naturally occurring lyretail in guppies, so it was called that in swords as well. A similar mutation in mollies is also called lyretail. Because lyretail is a dominant allele, any fish inheriting it will have a lyretail. A fish inheriting lyretail from one parent and non-lyretail (regular caudal shape) from the other is termed “heterozygous” for lyretail. The “zygous” portion refers to zygotes, which are fertilized eggs. The “hetero” part refers to the fact that the zygote has two different alleles, in this case, the dominant lyretail and the recessive normal tail. The opposite of heterozygous is “homozygous,” where “homo” means “same.” A homozygous fish has inherited identical alleles. A fish heterozygous for lyretail will be a lyretail, while a fish homozygous for non-lyretail will not be a lyretail.
An interesting side effect of the lyretail allele is that it also causes the leading fin rays of the dorsal, ventral, and anal fins to be elongated as well. This has implications for males carrying the lyretail allele; their gonopodia (penis like structure used to insert sperm into females) are too long to function. While lyretail males produce sperm, they can’t place it into a female, so are functionally sterile. The upshot of this means, absent the use of artificial insemination, it is not possible to produce homozygous lyretails. As a result, all lyretails are heterozygous. The males can’t be used for breeding and, therefore, females are mated to non-lyretail males. Such matings produce (on average) 50% lyretails and 50% non-lyretails since the females are heterozygous and carry the allele for normal tails (for more about this and a possible solution, see my blog http://goliadfarms.com/red-lyretail-swordtail-experiment/). This mutation has been transferred to maculatus and variatus via hybridization.
The fish shown below is a male Redwag Hifin Lyretail Sword. Note his elongated gonopodium (the long fin under his belly), which makes him functionally sterile.
Hifin is another allele of a gene that regulates dorsal fin ray length. It, like lyretail, is a dominant allele. A fish heterozygous for hifin will have a hifin. This allele causes the fin rays to grow several times the length of normal dorsal fin rays. It affects only the dorsals, so hifin males don’t have the gonopodia problems of lyretail males. This mutation arose in the 1960s in a sword strain of a woman named Simpson and, as a result, were long known as Simpson hifins. The mutation has been, like lyretail, been bred into maculatus and variatus strains.
Unfortunately, hifin is a homozygous lethal. Embryos with two copies of hifin die prior to birth. As a result, all hifins are heterozygous. When mating two hifins (both of which are heterozygous), you won’t get the expected 3:1 ration of hifins to normals, but will instead get about 2:1 due the missing one quarter homozygous hifin embryos. The result being that a pure breeding line of hifins isn’t possible (for a discussion of a strain of hifins where the hifin allele appears not to be homozygous lethal, see my article at http://www.tfhmagazine.com/details/articles/life-with-livebearers276902.htm).
Plumetail is a dominant allele affecting only the caudal (tail fin), but is an allele of a different gene than is lyretail. The mutation causes the mid rays of the caudal to be extended, reminding someone of a plume, hence the name. Since plumetail doesn’t affect the gonopodium and is not a homozygous lethal, it is possible to produce a true breeding strain of plumetails.
Complicating things, each of these three fin types are subject to modifier genes that make them grow even longer, branch more, etc. The difference between a so-so lyretail and a spectacular lyretails is the accumulation of modifier genes that improve the base lyretail. The same applies to hifin and plumetail. The fantastic hifin swordtails of breeders like Karl Trochu at Miami Swordtails (http://miamiswordtails.weebly.com/) and Darrell E. Mefford are the results of master breeders taking the time and effort to accumulate the necessary modifier genes to create them.
Okay, with the basic genetic information out of the way, let’s proceed to how we introduce such fin type genes into our commercial strains. I’ll use our Red Tuxedo Swords as an example. The photo below this paragraph shows a typical male of this strain. We developed our strain of this fish from selections of our Black Swordtails. This latter strain we acquired from a Florida fish farm in 2003 after we were restocking from losses caused by Hurricane Claudette. Once we got the Black Swords we set out to improve the strain. The black body of Black Sword comes from a dominant allele causing a “tuxedo” pattern (the black bar along the length of the body) combined with modifier genes that spread the black. We also selected for Black Swords with the wagtail pattern (black fins), which in turn requires alleles of three genes, two from Xiphophorus maculatus (maculatus platy) and one from X. hellerii (green swordtail). I’ll deal with these three genes in a future blog. In January 2007, while processing one of our Black Sword strains, I noticed a few fish that were Black Sword culls, but had red bodies, tuxedo patterns, and wagtails. Rather than buy Red Tuxedos from another source, I decided to work with these fish. Why? Well, because we’d spent time selecting for size and these “culls” had nice size and a pleasing color. So, our Red Tuxedo Sword strain was born. I set up the best couple males and a few females in a breeding colony. After a few generations, we had a nice Red Tuxedo Sword strain, popular with our wholesale customers. The strain bred relatively true as the few non-tuxedos were purged each generation.
The fish below is breeder male Red Tuxedo Sword. Note his size. We select for large males. Also, note his brighter red color than the female at the beginning of this blog.
Recently, I decided to lyretail to the Red Tuxedo strain. To do this, I simply threw into the breeding colony a couple of Redwag Lyretail Swords. I chose these fish since they would not only add the two fin types I wanted, but would also help improve red coloration and would maintain the black fins I liked. Now, if one had unlimited time, labor, and space, you would done this cross in a separate vat, not in your main breeding colony. But, time and labor is a limiting factor in our hatchery. And, Susie (wife and business manager) takes a dim view of tying up valuable vat space unless it’s completely necessary. We don’t always agree on necessity. You’d think having about 800 total vats, vat space wouldn’t be a problem. But, Susie does spreadsheets and stuff to track revenues per vat. She insists each of our vats contribute profit. So, I deal with the problems associated with adding extraneous fish to our breeding colonies just to maintain good spousal relations.
What were these problems? To start with, the added females were already mated to Redwag Swords and their first offspring would be Redwags. This required some sorting when the breeding colony’s offspring were next processed. Secondly, hybrid offspring were heterozygous for the dominant tuxedo pattern, carrying non-tuxedo. That meant I’d have additional culling of non-tuxedos to do in the future. After the second breeding cycle and perquisite grow out time, I had Red Tuxedo Lyretails. The best of these females were added to the breeding colony. As I accumulated good lyretails with the red tuxedo color pattern, I gradually replaced non-lyretail females.
Having introduced lyretail and largely cleaned up the resulting genetic mess, I recently set about to add hifin. To do this, I added a couple of Redwag Hifin females and a nice large Redwag Hifin male. The result will be another genetic mess, but a few generations will fix that. I will favor Red Tuxedo Hifin males and Hifin Lyretail females to maximize the lyretail and hifin fin types.
The photo below shows a Redwag Hifin Sword male like the one I added to the Red Tuxedo Sword breeding colony.
Finally, to add plumetail to the mix, I’ll place some female Redwag Plumetail Maculatus into the breeding colony. In time, these females will mate with Red Tuxedo Sword males. Hybrid sword maculatus fish are fairly easy to determine; so, once I get some, I’ll pick the best plumetail hybrids to add back to the breeding colony. A few generations of back-crossing to produce fish with sword bodies and nice swordtails will produce Red Tuxedo Plumetail swords.
The photo following is a female Redwag Plumetail Maculatus like the ones I will add to the Red Tuxedo Sword breeding colony to introduce plumetail.
When I have enough good lyretails, hifins, and plumetails in this strain, I’ll build a breeding colony consisting of perhaps and three Hifin Red Tuxedo males and about 40-50 Hifin Lyretail Plumetail Red Tuxedo females. This breeding colony will produce Red Tuxedo Swords, Red Tuxedo Hifin Swords, Red Tuxedo Lyretail Swords, Red Tuxedo Plumetail Swords, Red Tuxedo Hifin Lyretail Swords, Red Tuxedo Hifin Plumetail Swords, Red Tuxedo Lyretail Plumetail Swords, Red Tuxedo Hifin Lyretail Plumetail Swords. Given the breeding colony, can anyone figure out the expected ratios of these fin types?