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Thread: One peculiar fish

  1. #1

    One peculiar fish

    So, my buddy has a pair of Angels that spawned several times yielding over 1000 viable fry. Male g/g, S/+. Female gm/+, s/+. The offspring all look like you would expect: silvers, ghosts, gold marbles, gold marble ghosts, blushers...all in the expected proportions. Then there is one dark fish. This begs the question: is this a spontaneous reappearance of the "D" dark gene or something different.

    If it is the known "D" gene, the fish is not dark enough to be a hybrid dark. It looks like D/+, S/+, that is to say it is a dark gray with a vaguely visible spot like you would expect.

    In a month or two this fish will reach breeding age. Do you have any particular suggestions on who try to pair it with in order to figure out if this is the usual "D" gene or something else? Has anyone had a similar experience? If so what did you find?

  2. #2
    It's a quite common and well documented phenomenon.
    Firstly it helps to know that Gold, gold marble, Marble and Dark are all alleles, that is to say different versions of the same gene, there is a fifth allele which is the unmutated version "wild type" of the gene.
    Secondly it helps to know that the first statement is based on research carried out by Dr Joanne Norton in the 1970's & 80's and is therefore based on traditional Mendelian breeding experiments rather than on gene sequencing. With Gene sequencing becoming easier and more affordable, hopefully it won't be long before someone carries out the necessary work to more accurately explain what is going on, however we can make some educated guesses based on the information we do have.

    I have personal experience of this mutation occurring on several different occasions and with several different parent fish, and there are multiple reports of it happening to other breeders, it usually happens where the parent fish are gold marbles, but that may reflect the frequency with which gold marble are bred compared with marble or plain gold.

    This thread on TAF II for instance
    and here's a case I documented where the parent fish were marble rather than gold marble

    and another
    and another

    You may notice that the term I searched for was "crossover", personally I'm not convinced that this is a true crossover event. My personal suspicion is that the Marble gene arose as a result of gene duplication whereby a dark gene was inserted adjacent to a wildtype gene it then being a matter of luck as to which of the two copies becomes activated, if the wild type, you get a silver patch, if the dark, a dark patch.
    similarly with gold marble I suspect a gold and a dark gene to have become similarly linked.
    One potential effect of this is that if a fish is heterozygous for one of the marble genes with either a gold or wild type version of the gene as it's analog on the other chromosome there will be a mismatch in the length of the chromosomes when they pair during cell division, as a result the marble gene will form a loop making it more vulnerable to modification by the cell's "proof reading" enzymes. When this happens it's more obvious when the dark gene is left behind rather than the gold or silver version.

    Your case however sounds slightly different, My expectation would be that it was the female parent who provided the mutation the Gm/+ combination being ideal if the mechanism I suggest is correct. If however the fish is in fact D/+ that would suggest that the mutation occurred in the g/g male, which would point to a rather different explanation than my hypothesis.

    So in answer to your question, I would mate it to a gold angel, in the expectation that it's D/g and you'll see 50% gold offspring. If you get 50% silver offspring, indicating that it's D/+, that will be a significant observation.
    Please keep us informed of results/progress, photos of parents and the fish in question would be much appreciated.
    Blessed are the cheesemakers!

  3. #3
    Thank you for the information. what you say makes sense to me, that is, since this is all on the Dark Locus it is more likely a small slip than a spontaneous appearance of a totally new genetic mutation. Next time I visit I'll get some pictures to upload of the parents and and this one offspring.

    thanks Pterophyllum.

  4. #4
    This curious dark fish is now an adult female and spawning. Soon we should have some results to see what happens. The male is a Koi Gm/Gm. S/S.

  5. #5
    excellent, looking forward to seeing the results.
    Blessed are the cheesemakers!


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