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Gambusia Affinis x Poecilia reticulata, Can it be done?

Discussion in 'Livebearers' started by gadadhoon, Nov 19, 2016.

  1. gadadhoon

    gadadhoon New Member

    Nov 19, 2016
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    The short version:

    I spent nearly a year working it out methodically. My answer is ‘maybe’. It certainly isn't easy though, and no one has proven it so far. If you want to spend a year carefully observing some dull colored fish have at it, just don’t stick a female guppy fresh from the store into a tank with some male mosquitofish, wait for fry, and claim victory.

    The long version:

    Many people have wondered if guppies can be crossed with western mosquitofish. After all, mosquitofish look quite similar to feeder guppies and both are closely related livebearers. There are several discussion threads and youtube videos of people either claiming to have done it or documenting their attempts, but no detailed explanations of methods. AdrianHD, who has bred many new strains (see his web site), has successfully cross-bred Gambusia Vitatta with wild guppies (reference 2), so cross breeding Gambusia affinis with guppies isn’t out of the question.

    Unfortunately hybrids are difficult to verify, because livebearers store sperm and can give birth to several batches of young from one fertilization. Sometimes they can skip a batch or two, and a female guppy who hasn’t seen a male guppy in months can suddenly and miraculously give birth. Because of this females bought at the store can appear not to be pregnant but then go on to give birth. The “gravid spot” on the side of female guppies is really a semitransparent window into the abdomen found (to some degree) in both males and females which becomes more visible whenever something distends the belly, so it’s a uniquely poor guide when one is trying to decide if a female guppy has been fertilized.

    I set out to cross-breed Gambusia Affinis and Poecilia reticulata with truly virgin female guppies. I chose female guppies and male western mosquitofish because of a study which showed successful crosses between male western mosquitofish and female eastern mosquitofish, but failed to show successful crosses of the reverse genders due to what is essentially a killer sex chromosome (reference 1). Also, as anyone who has kept mosquitofish can attest they are nasty little buggers and putting a colorful male guppy in a tank of female mosquitofish would eventually produce a dead guppy.


    Obtained male and female guppies from the store. They did what guppies do, and the female guppy was isolated from the male guppy in a separate tank. I failed to document the exact day on which she gave birth due to interference from my day job, but was taking regular pictures so I know it was some time in the week or two after March 12, 2016 because I have a picture of her pregnant on that date and a picture of growing fry April 9. Here is the pregnant guppy:

    After the fry were born they were allowed to grow until subtle sex differences became visible. Fry growth was slow because I keep my tanks around 72F. An attempt to separate the males from the females based on subtle differences was made 4/9/16. Using our estimate birth date the fry would have been about 3 weeks old.

    Unfortunately one male developed late. He was recognized by the first hints of color in his tail, and taken out of the tank. Final isolation from all male guppies occurred 4/18/16, just shy of one month of age. Here is a picture of what the female guppies looked like at the time:
    When separated the male guppy had not yet developed a gonadopodium. Also it had not yet started attempting to mate with the females or “court” them in the nose-to-anal-fin fashion which guppies do.

    The guppies were allowed to develop normally. Tank mates included (at various times) a male betta fish and a Florida flagfish, neither of which are livebearers.

    A male mosquitofish was obtained from the local vector control and added to the tank 6/22/16. After a short acclimation period he began courting the largest of the three female guppies and frequently attempting to mate.

    Here is a video from 8/7/16 documenting the courting behavior. Actual mating attempt at 1:33.

    The largest female guppy continued to be quite plump with an obvious gravid spot. Unfortunately the experiment met its end 10/25/16 when the female guppy ate a concentrated drop of plant fertilizer I was dripping into the tank and died. The next day a post-mortem dissection was performed, showing a large number of eggs which did not appear to have internal features, suggesting they were unfertilized. Guppies are ovoviviparous, so the discovery of unfertilized eggs was not earth-shattering.

    In conclusion, the end result of placing a amorous male mosquitofish in a tank with a bunch of virgin female guppies is a lot of guppy-rape without a lot of results. This may be due to differences in gonadopodium structure or genetic incompatibility. I encourage anyone who wants to devote a tank to the study of rather dull fish for a year to check my results, maybe others will have more luck with different sex ratios or water parameters. Speaking of which, temp 70-74 (low to suit my temperate species), pH 8.0-8.3, water very hard, though I don’t remember exactly how hard off the top of my head. Nitrates trace to undetectable except after fertilizing due to plants in tank and algae from bright lighting.


    1. Black, D. A., & Howell, W. M. (1979). The North American mosquitofish, Gambusia affinis: a unique case in sex chromosome evolution. Copeia, 509-513.

    2. http://www.fishforums.net/threads/hybrids-of-mine-gambusia-affinis-x-poecilia-recticulata.200028/

    3. Shikano, T., & Taniguchi, N. (2005). Relationships between brood size and offspring body size in an ovoviviparous fish: maternal effects and genetic trade‐off. Journal of Experimental Zoology Part A: Comparative Experimental Biology, 303(8), 635-642.
  2. BettaBettas

    BettaBettas Member Preview

    Aug 7, 2016
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  3. Galejoy

    Galejoy New Member

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    Good day!
    I once had a casual tank of breeding guppies mixed with locally wild-caught species of assorted fish (basically anything that would fit in the 25 gallon aquarium was fair game!).
    Originally, I had caught a wild female mosquitofish before I introduced any store-bought guppies.
    Several generations later, after the immense guppy proliferation, the older mosquitofish showed signs of pregnancy, with a very large gravid spot and stomach. I was pleasantly surprised that see it was possible for her to be impregnated by common guppies, but unfortunately she died in later stages of embryo development because of the onset of a sudden disease in the aquarium.
    I was hoping very much to see if a hybrid could be born. What a shame! :(

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