The most thoroughly studied group of fish for the genetics of sex determination are the platyfishes and swordtails of the genus Xiphophorus (for detailed reviews see Kallman, 1984, Kazianis et al., 2004 and Volff and Schartl, 2001). These fish nicely demonstrate the variability of sex determination systems in fish.
In the platyfish, X. maculatus, three different sex chromosomes: W, X, and Y occur. Females may have WY, WX or XX genotypes. The males are either YY or XY. Interestingly YY males are fully viable and fertile, indicating that no essential genes have been deleted during the evolution of the Y. WW females have not been found in natural habitats, but can be produced in the laboratory and are viable as well. Sex determination in this three chromosome situation is explained at present by two different hypotheses: The first ( Kallman, 1984) proposes a network of male determining genes and regulatory genes distributed over the different types of sex chromosomes and autosomes, while the second ( Volff and Schartl, 2001) favors a dosage dependent mechanism based on one gene being present in different copy numbers on the three types of sex chromosomes. The stable sex chromosomal determination mechanism in the platyfish can be overridden by rare alleles of autosomal modifiers found in some natural populations (Kallman, 1984) and by exogenous influences, e.g. X-ray irradiation (Anders et al., 1969) and steroid hormone treatment (Dzwillo and Zander, 1967). For the green swordtail, X. hellerii, some strains have been shown to be WZ–ZZ ( Kazianis et al., 2004) while others exhibit a so-called polyfactorial system ( Peters, 1964), meaning that the sex-determining genes are spread over several chromosomes, which additively or cooperatively influence gonad development. Other species like X. variatus and X. xiphidium appear to exhibit a simple XX–XY sex determination mechanism. A modification of the XX–XY system is described for two species, X. nezahualcoyotl and X. milleri. Most males are XY and most females are XX. However, a second Y chromosome, Y′, exists, which together with an autosomal modifier is responsible for XY′ females. Consequently, YY′ males can be produced ( Kallman, 1984). Another modification of the XY system was found in X. nigrensis. In this species all XY fish are males. There is an autosomal locus with two alleles, A and a, which affects sex determination in XX fish. If the genotype is AA, the fish will be female, and if aa, the XX individual will be male. Aa genotypes are predominantly female, but sometimes (approx. 5%) such fish develop into males ( Kallman, 1984). Attempts towards isolation of the sex determining gene(s) in Xiphophorus are underway. BAC contigs starting from marker loci that flank the sex determining region on the X. maculatus X and Y chromosomes have been established covering at present approx. one megabase on each side ( Froschauer et al., 2002). Source: A comparative view on sex determination in medaka
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A- Peppermint male x Ruby red female: 100% F1 looked like the mother (Ruby red) This is a full-white Peppermint male swordtail. He used to have red pigment on half of the body, but the red pigment was gradually suppressed, thus he turned out to be a full-white individual. He was crossed to 2 Ruby red females to test if the traits is recessive to normal red color. Both results harvested 100% red offspring. All are well developed and totally look the same as their mom. No red pigment suppression is found along their development up to 3.5 months (some of the juveniles mature to be males at this age). So, the trait [peppermint] is recessive. (See the video below to better view the male's color. He's so fast to be caught in my phone camera.) In this case, I hypothesize that the RPS [Red Pigment Suppressor] gene required a homologous pair to express. As a matter of fact, the backcross of F1 to its father should express peppermint trait in F2. In case of the father didn't survive during the breeding project, I will interbreed F1 individual to each other (3 pairs) with the hope to reproduce the RPS trait in F2. The Fish Culturist, Volume 1 (This is the first issue of THE FISH CULTURIST, a monthly publication inaugurated by the Pennsylvania Fish Culturists’ Association.)
- Orange Swordtail, of C. Vowinkel. - Green Swordtail, of J. R. Guckes. - Platypoccelia Pulchra, of G. Pocock. - Platy. Rubra, of J. S. Nelson. - Platy. Nigra, of G. Pocock. The Board of Directors reported recommendations to limit the swordtail-moon-lish hybrids to three classes for the purpose of the current competition, eliminating the so-called “red-head" hybrid, as being merely a color phase of the rubra hybrids and pulchra hybrids, being found in both crosses; (The Fish Culturist, Feb 1921) A couple first of my breeding projects weren't very successful. Among dis-satisfactions were the size of swordtail progeny which is smaller than their parents. I also noted that youngsters proceeded early sex maturation, which could be the reason for the reduction of growth rate or even cessation of body growth. There're couple things that control the maximum potential size of my swordtail could reach: - Inheritance - Diet - Captive environment - Early sex maturation A- Inheritance: I usually see Kohaku koi swordtail at medium to small size when purchasing them from Aquabid breeders and local fish store. As far as I was told Koi swordtail is among the youngest strain created in late '90. It is clearly that this strain was a hybrid. An origination of Platys ancestor as well as long time interbred could have contributed to its small size in comparing with other swordtail strains. So, a cross breed with "giant" swordtail would help to improve the situation. Nevertheless, crossbreeding a Koi swordtail individual to another strain of Swordtail would significantly decrease the quality of bi-color band. And "Koi" coloration is still mysterious to me. B- Diet: The fishes are fed with Brine shrimp twice a day, and Hikari pellets for livebearers during the day. C- Captive environment: At the moment, I could only keep 20 gallon tanks in my recreation corner. So the population is often around 20 swordtails each tank. Water change is done weekly at 80-90% and all tanks are treated with Aquarium salt to promote acclimation. The temperature is maintained at low optimal 70 - 72 Fahrenheit. D- Early sex maturation: I believe that social environment has some effects on early sex maturation. From my observation, late mature males usually develop bigger body size; but these males in my tanks were usually those being bullied by a dominant character which made them often hide away for a long time until they were bigger and stronger to fight back. Then I found interesting piece of journal mentioned that "females and males adjust their age at maturation in response to visual cues of male sexual ornamentation in the current environment: females matured earlier, whereas males matured later if all the mature males seen had large ornaments" (Walling et. al., 2007). So, I designed that as early as a male is sexed out, I placed him in the male tank and hoping that the aggression of dominant males would slower his maturation due to suppression. Without any female in the male tank, it seemed that dominant males were also less aggressive after all. That way, females would be preserved to be virgin, avoid sexual harassment from males, and fully developed until they are ready for brand new breeding projects. - Males and females are separated as soon as they are sexed out. - The effect of having a dominant male may help suppress the sex maturation of the others, thus leaving more time for the other males to fully develop. - Females would also have more time to develop if avoid sexual harassment from male swordtails. Citations and References: Green swordtails alter their age at maturation in response to the population level of male ornamentation Craig A Walling, Nick J Royle, Neil B Metcalfe, Jan Lindström Biol. Lett. 2007 3 144-146; DOI: 10.1098/rsbl.2006.0608. Published 22 April 2007 Females matured earlier in the long-sworded treatment than in the short-sworded treatment, while the converse was true for males. Females from the long-sworded treatment were smaller than females in the short-sworded treatment, whereas males did not differ in size between the treatments. (Walling et. al., 2007) The white male in video clip is offspring of Marlboro swordtail, however its red pigmentation decreased over the time and eventually disappeared; at the moment, he is totally white with a horizontal light neon blue along his body. I haven't got any knowledge about Marlboro swordtail, but so far I heard that it's normal for Marlboro swordtail to partial or totally lose its red pigmentation over developmental stages. My questions are: - Is red pigmentation fixed when a red swordtail is born or the pigmentation is produced consecutively during its lifespan to maintain the red color? - Is there a gene factor that suppress the red pigmentation production which caused the loss of red pigmentation (LP) in Marlboro swordtail? - Will LP a dominant or recessive inheritance factor? - What happen if I cross this Marlboro male to normal red female or to a albino red female? Advantages: - This male is active breeder, he loves chasing after a huge size red female. Disadvantages: - This strain I collected from a farm in FL. He was shipped together with his siblings (males and females) but all of them suffered heavy fungus on the way to my place. Only him recovered and survived which is showing his good resistance, but not sure if the past disease had any effect on his fertility. He's the smallest swordtail comparing to his siblings. Breeding model: Due to limited time and space for my hobby, my swordtail fries are often kept in common tanks categorized by size range during their developmental stages. This avoid small bodies from starving due to food competition. Culling process usually goes along with each stage, thus it make my tracking list much easier for record and observation. This breeding scheme is to observe if LP has any effect on Albino red. Next step: - I will cross this male to normal red female in another project. - And his offspring with Albino red female in this project will be back cross with the father and to its sibling to see if the effect get stronger (double dose or triple dose, maybe) P:
♀: Albino standard Koi pattern, normal dorsal fin. ♂: Albino, blood red, sail-fin. F1: In general, I obtained 100% albino, mostly white body at birth; light orange color visibly expressed at 3 days old, and Koi pattern is visible at about 1 week old. At birth: 40 counted, not sure how many were re-absorbed by the mom (no breeding net deployed).
Some disadvantages: - Limited tanks and breeding supplies for the project. - Set many standards within this very first try. Only one trait should be tested and harvested at a time would likely increase the success. - Cannot keep up with regular feeding and water changing schedule, thus affecting the growth rate of the filial. 1. All fancy strains of swordtails (Xiphophorus hellerii) have mixed ancestries with Xiphophorus maculatus (moon platies) and/or Xiphophorus variatus (variatus platies). 2. The first Xiphophorus helleri showing an elongated dorsal appeared in the late 1950's in one of Mrs. Telma L. Simpson's fish tanks. This housewife turned fish breeder kept working with that single male until she fixed the trait. It is from her South Californian hatchery that it all started. In the 1960's and 1970's, top breeders developed all kind of fancy strains of both swordtails and platies… up to today. The most famous (to named a few) are Dr. Joanne Norton, Fred Morita, Glenn Takeshita, Rosario Arijon, Darrell E. Mefford, Bobby Ellermann, and Dr. Roy Levine. To read more about the complete history of hifin swordtails, read Mr. Ellermann’s most excelent article: 3. Two low-fin swordtails (that is fish with regular dorsal fin) will NOT produce hifin offspring, even if they have hifin parentage in their blood line. If they were to, then one would have just duplicated Mrs. Simpson’s original hifin mutation. If not technically impossible, still highly improbable... I have lately been made aware that Greg Sage of selectaquatics.com from Colorado has raised a strain of HIFIN Xiphophorus Mayae, so the gene mutation has once again naturally expressed itself. 4. Two hifin swordtails will always produce a small percentage of low-fin offspring. As far I know, there is no homozygous hifin for the Xiphophorus genus. Also a cross between low-fin and hifin swordtails produces roughly 50% hifin offspring. 5. SAILFIN swordtails are nothing more than a 'descriptive label' for HIFIN swordtails possessing an elongated dorsal fin with more branched rays, hence producing a sailfin looking dorsal (both wider and longer). Think of them as 'la creme de la creme' in breeding hifin swordtails. Such specimens seem to posses a genetic modifier allowing their dorsal ray to branch out. At least it is my limited understanding of it. 6. How are "sailfin" swordtails produced? Simply by selective breeding, culling, and hard work. The genetics of hifin swordtail is complicated and yet not fully understood. It is clear that if a strain of sailfin swordtail is not drastically maintained, it quickly regresses to producing more basic hifin fish. If one wishes to understand more about the genetics and science of hifin swordtails while viewing photos of splendid fish, then simply visit Dr. Levine’s website… everything you ever wanted to know and/or understand about hifin swordtails is there. 7. American Livebearer Association which is an organization worth belonging to if one is interested in livebearers in general. Most members are more into wild livebearers, but a few dedicated breeders of fancy Xiphophorus are still hanging around. A FEW LINKS OF INTEREST: - Dr. Roy Levine - http://www.xhifin.org/ - An authority in genetics of Xiphophorus fancy finage, and a true hobbyist at heart. His results and photos speak for themselves. - A great hobbyist breeder; of fancy Xiphophorus: Ela from Poland: http://xiphophorus-ela.blogspot.com/ - German website dedicated to Fancy strains of Xiphophorus: http://www.platys.net/ - An inspiring senior fancy Sail-fin swordtail breeder - Mr. Karl Trochu: http://miamiswordtails.weebly.com/ - If you are interested in wild and/or fancy xiphophorus, feel free to join this specialized Facebook's page:International Xiphophorus Breeder - French Livebearer Association: http://france.vivipare.free.fr - German Livebearer Association: http://www.guppy-molly-xipho.de/ To anyone who is seeking for quality specimens, two commercial breeders who produce exceptional fish are recommended by Mr. Karl Trochu " If I had to get any livebearers, I would get them from those two hatcheries, period!" - http://selectaquatics.com/ - Greg Sage form Erie, Colorado - USA - http://goliadfarms.com/ - Charles and Susan Clapsaddle from Goliad Texas - USA This post is credited to Mr. Karl Trochu and his website at http://miamiswordtails.weebly.com/ |
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