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  1. #1

    Koi Developed a Tri fin?

    Hello everyone,

    I'm new here and this is my first post, I have done some google searches and searched the forums on here before asking and couldn't find an answer to my question even though it's probably pretty obvious to you lot.

    Basically me and my wife brought a bungalow and in the process inherited a Koi pond, we absolutely love them but really lack the knowledge surrounding their health, we have already spent hundreds of pounds on things like pumps, filters, air stones, new liner ect..., however, I have recently noticed that some of the Koi have developed what I can only describe as a tri fin (their tail fin looks like the back of an aeroplane).

    I first noticed it on some of the smaller koi in the pond but has since (over about 1 month) spread to some of the larger Koi in the pond. Not all the Koi are affected and it seems completely random as to which ones are.

    I will attach some pictures to show what I am talking about, sorry they are not very clear my Koi are fairly camera shy. I have outlined the fins you can see in the picture in red.

    Any and all help is very much appreciated.



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  3. #2
    are they hybrids resulting from a pond breeding with mix parents?

  4. #3
    Hi Familyman, I'm sure there are hybrids in there, however, I failed to previously mention that when we first got the Koi they did not have tail fins like that, every single one in there was completely vertical and straight. This happened around a month and a half after that.

  5. #4
    lol, I'm stumped then, I don't see how they can just grow a tri fin tail all of a sudden

  6. #5
    Extreme Koi Member Rank = Yonsai anne's Avatar
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    May 2010
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    It looks as though you have a mixed pond of koi and goldfish and the fish you have circled looks like a
    Wakin Goldfish to me ? had one years and years ago, see if you can find a picture of one and compare it to the
    fish you have in your pond .

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  8. #6
    Extreme Koi Member Rank = Nanasai Scamp's Avatar
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    Nov 2014
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    Hi Billy
    are you sure they are not huge fantail goldfish, and you’ve just noticed the tail? If definately just developed from a normal fin, then i have never heard of that! Good on you investing time and money looking after them when you moved in.

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  10. #7
    Extreme Koi Member Rank = Mature Champion john1's Avatar
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    Aug 2013
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    Hi Billy,
    I think they look like a large goldfish of some sort,leave it to Anne to have a look,good of you to bring it up at least you are taking care and notice of them.

    They all look healthy enough which is the main thing any more advice you need we are here for you.

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  12. #8
    Extreme Koi Member Rank = Supreme Champion Andy1671's Avatar
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    Sep 2014
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    I sold some fish like this in the summer and they were goldfish.
    A normal bodied goldfish but with a short sort of fantail.
    An unusual talking point in your pond
    5000 Gallon Fibreglassed Pond With 54" x 27" Infinity Window
    BD300 Drum Filter
    Artesian 0.5hp - Aquadyne 4.4c Beadfilter - PS4 Protein Shower
    Badu Eco Touch - EP20 UV Sterilizer - ASHP - Venturi
    Hi Blo 60 - Medo 45 - Spindrifter Bottom Drain
    Wide Mouthed Skimmer

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  14. #9
    Do you live near Sellafield

  15. Thanks Andy1671, fishysteve, freddyboy, Cucumber_Man, anne Thanked / Liked this Post
  16. #10
    Senior Member Rank = Adult Champion 14crazychris's Avatar
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    Jul 2013
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    hi there
    to me that look like Carassius auratus (Gold fish) just very large ones. possibly a wakin variety as Anne said
    cheers Chris
    YouTube channel- brick4774
    3000gallon fiberglass pond
    CL3 filter and window

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  18. #11
    Firstly, a big thank you for all the reply's, what many of you have said is defiantly the most likley option, the "tri finned" fish defiantly look like Wakin Goldfish.

    I can only assume that I originally missed this and then just saw a few more over time making me believe that it had developed over time.

    Anyway that's a huge relief and it's amazing their resemblance to the Koi in the pond is astounding, but then again I am a newbie at all this.

    Once again thank you for all the reply's and help!


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  20. #12
    Extreme Koi Member Rank = Yonsai anne's Avatar
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    May 2010
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    We were all newbies once and all panicked at the slightest thing so your not alone there
    But at least your minds been put at rest and it looks nice and healthy.
    Oh, and no doubt you will have a few more panic modes but that's quite normal so don't be alarmed .

  21. #13
    Moderator Rank = Grand Champion Feline's Avatar
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    Aug 2013
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    The easiest way to tell for sure which fish are actually koi is to look for the 4 barbels round their mouth. Goldfish don't have these.

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  23. #14
    Extreme Koi Member Rank = Adult Champion pip895's Avatar
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    Nov 2013
    Nr Farnham, Surrey
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    I have some goldfish that apparently developed tri fins as they got bigger. When younger their lower tail fin didn't splay out in the same way but if you looked closely you could see it was split into two - very easily missed though.
    6000g unheated in ground koi pond
    +3000g lily/Anoxic pond attached
    26 koi (25 to 60cm)
    Bottom drain & Skimmer to Drum QK50 - PondXpert Variflow 30000 to 30" Lacron with 200 ltr micro K1
    Blue eco pump to MB, returned via Anoxic pond (30 baskets)



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