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C.venezualian — unusual specimen

Home Forums Fresh and Brackish Water Fishes C.venezualian — unusual specimen

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    This chap (left front) is entirely lacking the orange/red color component which is characteristic for the species. Notice in particular the dorsal fin, it should be similar, even a bit brighter, than that of the c.aeneus behind.

    The parents and 9 siblings are all normal.

    Does anyone know anything about this type of mutation? Recessive like melanin deficiency? Seen in other fish speucies?

    The little guy (2cm now) seems to be healthy but surely looks odd….



    Nice picture. Still has iridophores.

    Are you saying this is lacking red pigment and melanin or is just lacking the red?


    Of course you realize recessive pigmentation mutants are not uncommon in other species.


    If you think it is a recessive, it should have inherited a copy of the mutant from each parent. Do you know how closely the parents are related? A common grand-parent (or more distant relative) would explain both parents having the same mutation.


    You could cross your fish to the appropriate (proper sex) parent. One half of the offspring should be mutant.



    Thanks, Bill, :D

    Has iridophores, melanophores (camera reflection weakened the black, but it is normal), and possibly xanthophores (not sure if the yellow bottom is the muscle color or pigmentation). Erythrophores are the missing ones.

    No, I actually never saw recessive mutants other than albinos… it seems that the melanin production is the one thhiat breaks down easiest? Any danio examples?

    Parents are a problem :( I had problems with this fish initially, very bad quality, and two times I lost half of the fish I bought within a month… never lost any that survived this first month, but I ended up combining three groups together. Obviously some fish are related in each group but it is too late to know who is who, and who are the parents… i think there are 13 possible parents there…. :(

    I’m actually raising 30+ more offsprings, so there is a chance I will find another like this (too small to see yet). If not and if people think this is attractive, I can still get the strain going: cross this one with any other fish, either get half the mutants, or if not, all the offsprings will be carriers. And the fish is not all that difficult to breed, they are closely related to green/bronze cories. I’m just not sure this is a sane thing to do in this case: it is the orange that makes the fish attractive, I should take a photo of a normal, but meanwhile look here.



    Hi Mike


    Zebrafish will not be that much help with red pigments since the only red they have that I know of is their blood cells.

    However, most mutations are recessives. There are lots of different recessive pigmentation mutations in zebrafish. The mutations involved in patterning the pigmentation rather than just making the pigment go away are also mostly recessive. Longfin is a dominant mutation in zebrafish making… longfins, but there are also recessive mutants (in other genes) making longfins. The recessives are not so easily found.

    Perhaps mutations in melanin are easier to see and are therefore propagated more frequently.

    I recently found an apparently novel mutation I am calling emerald in some zebrafish I got from a petstore. It causes more iridophores and makes the fish look greenish if the light is at the right angle. This is a recessive mutation that looks like this in the proper lighting:


    This was in a mixed genetic background of a leopard danio. The leopard is a recessive mutant of pigment distribution. These fish might also have carried a known recessive mutation reducing melanin pigment (nacre). Point is its somewhat subtle and not obvious. So its unlikely to be noticed. Whomever made the leopard line probably bred the mutant in their fish because with the other mutants it made them look nicer.


    Assuming it turns out to be a mutation, its genetics could be interesting. You found one mutant phenotype in ten fish (10%). One would expect a quarter of the fish (25%) to show a recessive phenotype in a cross from two recessive carrying parents. This does not mean that it is not a recessive inherited from each parent, but it makes you wonder.

    If it were dominant, it would have to show in one of the parents. It is possible that something weird happened during its development that prevented the red pigment from developing. Another possibility is that a mutation arose in the one of the parents. If it is a dominant, that would explain everything. If its a recessive than one of the parents could have carried it undetected and another mutation would have to arise again in the same gene in the gonads of the other parent or in the fertilized egg. This is unlikely but not impossible.


    Personally, I would do the cross you suggest just to see if it is a mutant (one or two generations as you describe it). If it isn’t a mutant, you’d have a bunch more of the fish with the red. If it is a mutant you would still have a bunch more of the fish with the red anyway (mixed in with those lacking the red).

    Is anyone gonna want it? I don’t know, but you might know something about what is going on.




    Thanks, Bill,

    Very pretty danio — I’m assuming you are going to breed it and try to get a line?

    Don’t attach any significance to 10%. Firstly, when cories spawn, several males participate, and the same spawn would contain fry from different fathers. Secondly, these 10 came from different spawns: these are the first babies I got from the cories, the parents were very young at the time, and most fry was so weak that they died out… I was getting 2-3 survivors out of each spawn. (This improved as the parents matured, now most fry survive, this is why I have a tank of 30 babies). I’m guessing that out of 13 adults, two are siblings and carry the recessive mutation, but this does not help since I don’t know who they are.

    There is one more possible complication: the fish may not be a diploid.

    I probably will try to get a line… the fish may be less attractive than normal, but it actually looks intriguing next to them.

    As for long-fin: here is a puzzle: it is supposed to be a simple dominant mutation. Definitely looks this way for danios, plecos, and I suspect most fish: all longfin specimens look alike. But not for cories… on my photo at the beginning of the thread you can see a longfin cory… actually there are five in this tank, siblings I bred in spring, and all five have radically differently shaped fins! I should take careful photos, but the differences are such that I cannot understand how one gene is responsible for it… if the fish is a tetraploid this would be interesting.



    PS. Specifically, both the color morph and the longfin cory I mentioned are part of the c.aeneus complex (common green/bronze relatives) and I cannot track this down exactly yet but some cories are polyploidal. There is a paper that may give some answer:

    Turner, B.J., N. Diffoot and E.M. Rasch,1992 The callichthyid catfish
    Corydoras aeneus is an unresolved diploid-tetraploid sibling-species
    complex. Ichthyol. Explor. Freshwat. 3(1):17-23.

    I do not have access to this journal. Matt, per chance, do you? (I may be able to get a copy through a contact…not easy).

    And just what recessive/dominant mean in a polyploidal species may be interesting to find out.



    I’m assuming you are going to breed it and try to get a line?



    the fish may not be a diploid.

    That is very interesting.

    long-fin: here is a puzzle: it is supposed to be a simple dominant mutation

    Goldfish are tetraploidsor pseudo-tetraploids. It would be interesting to know what the goldfish genetics of longfins are like.

    There are longfin mutants in zebrafish that are recessive. One is called another longfin (alf).

    WRT the different longfin shapes, another thing to consider might be the different kinds of finshapes that happen in some livebearer lines (swordtails, lyretails, fantails, hi-fin, lots of different effects on different fins or on different fin rays within a fin).



    One problem with me getting a line is that the lifecycle is much longer than danios: you can get adults in 4 months, c.venezuelian seems to mature only at about 1.5 years. OK, I will try, the more I look at this fish the more I like it.

    Goldfish — maybe something is known indeed… not sure where to look, but I’m definitely not getting involved in experimenting with them…

    I do not know the significance but I actually have three lf cory species. lf paleatus are definitely not polyploid and the variance in fins is minimal comparing to possibly tetraploid c.aeneus. (The third species, lf panda, is too early to say… diploids, the parents seem uniform, but I got the first fry from them only yesterday…darned things take forever to mature. Minimum 4 months before I know.)

    I need to reread some books on genetics… My vague recollection is that in tetraploids only one pair of chromosomes is active, but is it the same pair in all parts of the body? If not, this will explain why some fins are long and some not.



    I’ll have to see what I can find out about goldfish genetics of dominants.


    My vague recollection is that in tetraploids only one pair of chromosomes is active, but is it the same pair in all parts of the body? If not, this will explain why some fins are long and some not.

    I have not heard of this going on with tetraploids.

    Mammalian X chromosome works that way in females (where they have two X chromosomes, males have only one X). One chromosome is randomly turned off after a bunch of cells have already formed, so different cells derived from these different founders will have different chromosomes active.

    There may also be some species of all female mollie that gets fertilized by a male of another species but inactivates the male derived chromosomes in this way. Different mollie species do this in different ways as I recall.



    If you dig up anything, this would be nice! Not necessarily applicable, but still very interesting. I’ll check scientific databases at work tomorrow too but really doubt anyone seriously studied this.

    (I cannot remember where it was anymore but I thought it was the same as with X).



    There is a theory that after a genome doubles there is genetic redundancy due to all the extra copies of genes and that the genome will gradually evolve such that the duplicated pairs of chromosome become distinct (so they only pair up and exchange DNA with the correct chromosome) and one of the two sets of duplicated genes becomes inactivated for particular functions.


    Somewhat similar, but over evolutionary times.



    Bill, do you happen to know anything about the genetics involved in hypomelanitic/amelanonitic fish?

    And also…maybe move this conversation to email or another forum? (too much downtime, and I am rather interested in the subject). My email is mvMONKEYpanix.com



    I finally found my goldfish genetics book.


    To finish off a line of discussion, here is what it says:


    Sadly, it seems that not many people are working on goldfish genetics much these days, so many questions are not as well addressed as they might be.



    Goldfish are tetraploids, apparently it is not obvious if they are autopolyploids (basically a doubled genome from a single species) or allopolyploids (a complex genome composed of two genomes from two different but closely related species in one animal).

    The second is more stable because the chromosomal mechanics of making gametes is less prone to error (which would generate non-viable offspring if chromosomes are not inherited properly).

    The two different kinds of polyploids can be distinguished based on the ratios of phenotypes from heterozygous crosses:

    autopolyploid homozygous recessive ratio: 1 in 36

    allopolyploid homozygous recessive frequency: 1 in 16


    Dominants and longfin phenotypes:

    The length of fin phenotypes in goldfish act as a continuously variable trait. Its assumed that there are many different genes affecting this trait and any distinct classes of phenotypes are blended into a continuous gradient of lengths.

    Since goldfish have a long history of domestication (over a thousand years) and longfin was one of the first mutants isolated in goldfish, additional genetic modifiers could easily have been unknowingly found and incorporated in the breeding stock, resulting in phenotypes dependent upon several genes (polygenic).


    The same argument (accumulation of genetic modifiers resulting in polygenic inheritance) is also used to explain the changing of some traits from dominant to recessive or from being lethals to being viable. This makes many comparisons with the genetics of other fish difficult.

    I would think that this is unlikely to be the case in fish that do not have a long history of domestication.


    Sex chromosomes: Goldfish seem to be assumed to have a doubled XX/XY sex determination system. Inter sex phenotypes are not common. Seems that the Y- chromosome acts as a dominant.


    Gene silencing has been used to explain the the phenotypic and inheritance ratios of telescope-eyed goldfish. This seems to be not something that happens all the time, but only occasionally. In later generations, the silenced gene can become un-silenced and can again affect the phenotypic ratios. This might be something like genetic imprinting or an epigenetic process.


    I couldn’t get you re-mail to work.


    To summarize what I know about:

    hypomelanitic/amelanonitic fish

    Very complicated. There are a lot of genes affecting pigment (reducing it or making it go away). Some affect the production of the chemicals involved in pigmentation in cells, and others affect the cells that would contain the pigment in some way.



    Thanks a lot, Bill,

    Very interesting, very scary. Loads of things I never knew about (sex chromosomes in goldfish … different schemes of polyploids). Is there some kind of overview of fish genetics I should perhaps read?
    My email has “MONKEY” to denote “@”…



    When I was reading that stuff, it was not clear to me that it was well worked out that the goldfish did in fact have a XY system of sex determination, but neither was it clear that they did not.

    Sex determining systems have evolved many times from situations where sex was not determined from chromosomal genetics.

    There are well known systems of sex determination based upon environmental conditions (alligators, based on temperature during their development in the egg).

    There are also systems where sex is determined by some kind of counting up of effects from many different weak sex determining genes scattered around the genome. Some think these weak factors may get grouped together on a chromosome to give it the power of a dominant sex determinant. There are probably other opinions on this also.


    The zebrafish (Danio rerio, a very well studied research animal) yet its sex determination has not yet been worked out. It does not appear to have sex chromosomes (at least in some of the laboratory strains). Researchers are now genetically mapping genes that have weaker effects on sex determination (like being one sex 60% of the time when a particular version of a gene is carried by an animal) and trying to get fish from wild populations that should be free of all of these kinds of influences.

    To add to the complexity of the situation, at least one of these zebrafish lines went through an all female generation at some point in its history. (This was done in order to be able to visualize and remove from the line all recessive mutations. This was done in order to have a genetic background clean of any mutations so that when new mutations were made, they could be collected witout finding the same old mutations that were already in the genetic background over and over again (which would be a big waste of time and money). In zebrafish it is possible to produce either haploid eggs (with only female derived genetics) or mostly homozygous diploid eggs (with genetics only derived from the mother). When the homozygous offspring of this generation of fish are raised some turn male and can be used to further propagate the line, which is done normally from then on.)

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