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Koi/Goldfish Hybrids

Discussion in 'General Cold & Temperate Water' started by Flaringshutter, Mar 27, 2009.

  1. Flaringshutter

    Flaringshutter Befriend a feeder!

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    There have been quite a few threads here in the past concerning koi/goldfish hybrids, and since recently I found myself the new owner of a hybrid, I thought I would share my research into the topic.

    First of all let me introduce my own young hybrid. He was sold to me as a "black comet" by a well-known vendor. I suspect the foreign wholesaler was not entirely honest with the vendor and I place no blame upon the vendor, who is well-known and has an excellent reputation. Either way, when the fish came to me I photographed it, as I generally do with new fish, and noticed while examining the photos that the fish had tiny barbels. This was my first clue. More on that later. Here is a photo first.

    His name is Sygnus, by the way.

    [​IMG]


    First of all, a bit about the...

    Viability & Genetics of Hybrids

    Koi carp (Cyprinus carpio) and goldfish (Carassius auratus) can hybridize in the average backyard fish pond, and while it is somewhat common, the hybrids are often sterile and do not reproduce themselves. In the wild, hybrids may or may not be sterile depending on the subspecies of carp involved. There are dozens of carp subspecies that may hybridize with introduced goldfish. For example:



    So depending on which subspecies is involved, the hybrids can be sterile or reproduce as easily as if they were full-blooded. As documented here:



    Additionally, some crosses may produce fertile hybrids of one gender but not the other. See the end of the first paragraph here:
    http://www.wdc-jp.biz/pdf_store/isj/publication/pdf/16/163/16304.pdf

    A bit more about the viability of hybrids between goldfish and carp subspecies here:
    http://www.cababstractsplus.org/abstracts/Abstract.aspx?AcNo=20053041051

    So my fish may or may not be sterile - we have yet to see.


    Anyway, I wanted to figure out precisely how to identify him as a hybrid...



    Identification Using Meristics

    First I noticed the barbels, and so I set upon researching the meristic (physical) differences between goldfish, koi, and hybrids.

    The most easily identified features include barbels, lateral line scales, and fin rays. An experienced goldfish or koi keeper will also notice body shape, mouth position, and fin shape, but these are highly variable between individuals and can't really be counted on for a solid ID. The best way is to use the shape and number of the pharyngeal teeth, those bony ridges in the jaws that help to grind up food. However, it's impossible to use those unless you kill the fish. So understandably, I wanted something a little less... uh, lethal.

    Lateral line scale count is one of the more reliable ways to ID a hybrid.


    Sygnus has 33 lateral line scales and 20 dorsal fin rays. He fits right into the hybrid range - on the low end for koi, too many for goldfish.

    Another marker is the presence of barbels. Koi have two pairs of barbels - one set just up and back from the mouth, another at the corners of the mouth.
    See here for photos: http://www.koiquest.co.uk/Anatomy.htm
    Goldfish have no barbels whatsoever, and hybrids either show no barbels or only one set, very small, at the corners of the mouth.



    Sygnus has one set of "reduced posterior" barbels, just visible against the rock here:

    [​IMG]

    You can see more photos of possible hybrids with similar small barbels here:
    http://www.koiphen.com/forums/showpost.php?p=1442380&postcount=5

    You will also notice them in this fish: http://www.tnfish.org/PhotoGalleryF...bridCommonCarpGoldfishMeltonHillNegus_jpg.htm


    As I mentioned earlier, an experienced keeper will immediately be able to differentiate between a koi and goldfish by body shape, mouth position and fin shape. These were the first features that tipped me off to the possibility that Sygnus was a hybrid. These are, of course, only to be used as...

    Informal Identification Keys

    Notice the differences in shape between him and one of the midnight shubunkins:

    [​IMG]

    [​IMG]


    Right away you should see that the hybrid has a much flatter belly line than the shubunkin's, which curves upward. The hybrid's mouth is set at the bottom of his head, while the shub's is midway between the bottom and top. The hybrid has round fins, the shub has pointed fins. This fin difference is even obvious between the hybrid and my common goldfish.

    Here you can see more details:

    [​IMG]

    See the rounded fins? Also notice those sensory nubs around the eyes - koi have them, goldfish do not. They are visible on the photo of koi eyes at the anatomy page I referenced earlier. I have seen them on some hybrids, but others do not have them. It may be another difference between subspecies hybrids.

    Other features that stand out to me were the thick, strong caudal peduncle - the muscle that connects his caudal (tail) fin to his body. Notice how much more muscled it is than that of the goldfish. The top photo shows this well. Also the lack of a V-shaped tail. The hybrid has a nearly solid triangle for a tail fin.

    In this photo you can just barely make out a very subtle hump between the end of his head and his dorsal fin. This hump may become more prominent as he grows older and larger. Some goldfish will develop a hump like this, and you will see it in many large koi. It seems to be a common characteristic among domestic hybrids.

    This website has dozens of photos of domestic hybrids: http://www.shortypen.com/koi/hybrid/index.htm


    This is a very quick and dirty look at hybrids and how to identify them, but you can find much more information by exploring the links I provided. Questions and comments are welcome! :)
     
  2. Kashta

    Kashta Always Niko's fault.....

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    Excellent article, Iris. This is a very useful reference for us. Thanks for posting this and for sharing the information you've collected.

    Given the usual length of goldfish vs. the length of koi, what would you expect the overall length would be for a hybrid as an adult?
     
  3. Flaringshutter

    Flaringshutter Befriend a feeder!

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    Well, since a common goldfish can reach 16-20 inches, and a koi 24-36 inches, a hybrid might fall anywhere between 20 and 24...28 inches, maybe? I would expect it to be an intermediate measurement, like the ray count and scale count. It's going to be a big fish by any measure.
    One also has to take into account hybrid vigor, so the hybrid fish may even grow larger than the numbers predict. I don't know if it could reach koi sizes. I'll do a little more digging on the hybrid size range.

    Glad the article is helpful! :)
     
  4. caitylee

    caitylee Yup....

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    That is a very informative read, I especially enjoyed all the links and pictures. Thanks!
     
  5. Flaringshutter

    Flaringshutter Befriend a feeder!

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    I was hoping the article would provide enough juicy scientific goodness to satisfy the more science-oriented fishkeepers - or at least point them in the right research direction - and enough basic info to assist your average aquarist curious about hybrids or looking to ID one.

    Be careful, if you click into those links you can end up spending HOURS in those research papers, haha! I always get sucked into them and use up half the day looking at brain scans and carp nasal canal structure analyses... science nerds exercise caution! :)
     
  6. ChilDawg

    ChilDawg Math is sexy.

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    Good warning! My students would probably get upset if I had the excuse "your papers weren't graded because I was looking at scientific journal articles on carp, goldfish and koi all weekend"!

    (Not even being facetious, either!)
     
  7. caitylee

    caitylee Yup....

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    Lol yes good warning! I just glanced at the articles because I'm at work and can't afford to get caught up haha.
     
  8. Kashta

    Kashta Always Niko's fault.....

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    I knew better than go looking at those. I've already lost weeks at a time reading up on things way beyond anything I actually need to know. It really is fascinating. Thankfully, we have Iris with us who doesn't have the sense to resist!! haha.

    I'm not going to be able to avoid them for too long, though. I have one of those hybrids now. Got this fish (red/white cross between some kind of butterfly koi and a comet) from a pond guy selling off goldfish. I told him it looked way too big and too bulky in body shape to be a comet or some kind of common with long finnage. He assured me this one wasn't a hybrid. I brought it home... no way does this fish not have some koi mix in her. I'll have to take some clear photos (if I can). She's truly beautiful, but already at 18 inches or so long.. I was worried about how big she's going to get.
     
  9. squabeggs

    squabeggs Fish Stix

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    Sygnus has got to be one of the coolest looking goldfish/koi I have ever seen....I want one! If I only had the water room. There is also a "mirror" koi that I want at my LFS...not sure if it is a hybrid. It is almost robotic in appearance...must get a pic.
     
  10. Teto

    Teto AC Members

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    wow! great article... i, am more interested in cichlids but i am planning a pond for this summer some koi/ goldfish wouuld look great on it
     

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