Fish of the Week: Koi with Spinal Deformity

A few months ago, I was at a koi sale and saw this guy swimming around a tub.


What do you think happened to this fish? It may have been a previous injury that never healed properly. Possibly this fish has had this defect since birth. Being the curious veterinarian I am, we took him over to Westside Animal Hospital in Santa Cruz to take some spinal x-rays. Apart from being a little skinny (it must take considerably more energy to swim with this deformity than a regular fish), this fish was behaving normally; eating and getting around his pond home like a champ! So, on to the x-ray table he went, albeit under slight sedation.



And what did we find? Well, his spine is certainly crooked, but overall, not in too bad a shape. As veterinarians, we look for clean X-shaped vertebrae with no fuzziness. Fuzziness usually means the bone has been irritated and started to deform itself. You can see this on the last few vertebrae in his back. Overall, this fish’s spine is a lot like a normal fishes, save for the S-shape.

So what is going to happen to this fish? Well, as long as he is eating a getting around okay, and has a good “quality of life,” he may just have to live with this. Research will be done to see if there is anything we can do to help him get a little straighter. Look for more posts about this guy in the future!

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6 thoughts on “Fish of the Week: Koi with Spinal Deformity”

  1. Hi! I have a koi that has the exact same deformity, his name is Fry. When I first got him he was perfectly straight, swam normally and still growing. But a couple of months after I got him, the filter broke down and it took me a few days to replace it. On replacing the filter I didn’t do a water change which effectively stirred up all the ammonia that had built up causing ammonia shock in all 3 fish in the tank. The two most affected fish were removed and placed into their own smaller individual tank (but without filters) with the water being changed regularly. Within 2 weeks Fry looked just like the fish in your picture; with an “S” starting in the lower thoracic region. All 3 fish lived but only Fry has the deformity. So I have 2 theories on the cause of Fry’s deformity; 1. it’s an effect from the ammonia poisoning, 2. its a result from the change in tank size. As you know, Koi have the ability to regulate their growth hormone secretion to suit their environment, so perhaps the switch to a smaller tank shocked his still growing body to stop secreting the hormone but his body responded unevenly. Any thoughts? If you’re interested in pictures, send me an email.

  2. Hi. I am quite late to this post. But will see if a reply comes my way. We have a 1/3 acre pond that had been stocked with some fish before we bought it. There were two koi type fish in it. (If more, they stay at bottom) one was bright orange and for sure koi, the other black and not as sure as it was more bashful. We added in 2016 4 more koi 4-8″. Have only seen one of those since then. The last two years we haven’t seen the black one. This year our orange one hasn’t been seen yet either. The newer koi is growing and social, BUT then out of the blue we now see this mammoth fish out of the blue. It is gray in color, with spine looking just like that. It seems to get around ok and is warming up to our presence. I dont know if I should be concerned about disease, or what. As I said, it is a huge pond, with what seems to be a healthy ecosystem. It has spotted bass, brook trout, perch and the koi along with a multitude of frogs. Outside of the 4 new koi, we have not added to this pond and are pretty sure nothing else was put in after 2012 when previous owner/hobbyist passed. Would happily send photos/videos.

  3. So what happened in the end? Did your research yield any remedies? How is the fish doing? Has it grown at a normal rate over the 7+ years?

    Very interested to hear updates.

    1. a woman in a lab coat smiling for the camera.
      Dr. Jessie Sanders

      Unfortunately, this fish was attacked by a bird of prey a year after this image. It would have been interesting to see how this injury progressed.

  4. We have a six year female old koi that has the same trouble. No hx of illness or trauma other than spawning activity. Her injury or whatever it is started about two years ago and seems to be slowly progressing. She eats well and has normal behavior otherwise.

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