Sometimes Diagnosing Koi Disease Is Quite a Challenge! - Play It Koi

In my 15+ years of experience working in the aquatics industry, both in Saltwater and now my newest found passion of Koi keeping, I've seen the good, bad and ugly in terms of systems, husbandry, and overall fish health.  In most situations where I'm called out for help, their sick fishes are fairly easy to diagnose.

9 X out of 10, id' say it's either: 

  • poor water quality due to lack of good husbandry
  • Inadequate filtration or sub- optimal equipment
  • or a parasite or virus due to lack of quarantining a newly found fish.

Yesterday evening though I was thrown through a bit of a loop on a new client visit I went out on as it met none of these 3 criteria. 

The client and I have literally googled for hours and still are stumped. I'm writing about my experience in hopes the koi community can help this customer get to the root of the issue and in turn, I'im hoping that this blog can help others in the future experiencing similar issues. 

----Synopsis --- 

Primary Concern: several of his fish have an unusual looking growth on their fins. Namely their pectoral fins, but some also on their caudal fins too. One of the larger koi appeared to have a slightly crooked spine. As of the last month, a handful has distended bellies with discolored white patches on their sides and heads. Another newer symptom (within the last month) is that a couple has now developed small round blistery pox-like bubbles on their backs. 

Physical examination: I visited the customer's house last night for the first time and we pulled one fish out for examination 

  • The fish had these Hard blistery like growths on its pectoral fins. These growths were tough, not something that could be scraped off. I would describe them almost as "wart" like. best I can describe it is that it seems like layers of tissue clustered together.
  • The gills both looked deep red. Of interest though, one side of the fish's gills we examined looked like it was a split in a few of the areas
  • Eyes appeared normal, not sunken
  • the scales on the side of the fish had several discoloration patches, I suspect from secondary bacterial infection
  • I took 6 skin scrapes on this one fish from all over (belly, gills, anus, sides, pectoral fins, etc) and looked at it these under a scope. Unfortunately, I saw no signs of parasites whatsoever which is surprising.
  • Note: While we only took one fish out. Some of the other koi showed signs of distended bellies. One even looked like it had dropsy as it was puffed out and pineconed. And one had lost a good chunk of it' tail to tail rot. I suspect these are an indication of a secondary bacterial infection is starting to take hold here.


Wart like growth on Koi Fish's dorsal fin

hard Wart-like growth on Koi's dorsal fin

hard Wart-like growth on Koi's dorsal fin

hard Wart-like growth on Koi Fish dorsal fin

hard Wart-like growth on Koi Fish dorsal fin

hard Wart-like growth on Koi Fish dorsal fin


  • Pond: Customer purchased home with a 20+ year established pond this past May. 3500 gallons ish. Poured concrete walls, no sealer on concrete. Filtration is run by 3 drum filters with old filter mats. No bottom drains. small/medium pebble bottom. NOte: There was a good deal of sludge and debris build up on the bottom. The Barrel filters were very dirty. Surprisingly though the water checked out.
  • Koi: pond contains several large fish. 5 x 3+ft koi that have had babies the last several years. In addition to the 5 big ones, there are probably 10 little ones ranging in size from 2 inches to 10 inches.
  • The customer hasn't added any fish since he purchased the home. He says some of the koi had the growths on their fins when he moved in, but it's gotten progressively worse with time and now as mentioned above more symptoms are starting to emerge (I'm guessing a secondary bacterial infection at this time)
  • No treatments to date.
  • Water parameters all checked out; PH 7.5, Ammonia & Nitrite both at 0, Kh 80, Temp 64-65.

Diagnosis ideas: Lymphocytus? Tuberculosis? Out of 6 skin scrape samples, I didn't see a single parasite (which was mind boggling in itself). I have no clue what the underlying primary issue is, however, I'm pretty confident there is a secondary bacterial infection now setting in. thoughts? 

Next steps? Obviously, I'm going to recommend he see a vet. Would you think we should start to treat the secondary infection at this time (water changes, heat, salt) or just wait until the vet can come out and go from there?

Any & all help on this challenging and unique Koi Health Situation is appreciated!!!!

Koi disease




Hi everyone I’m experiencing some koi health problems. I have observed behavior changes and have taken a very revealing underwater video of sores on my koi from flashing and scraping against a piece of slate in the pond. The Orange one seems a bit o2 deprive, but they all hang out by the water fall a lot. They are sporadically eating. Is there any way I can share the video to get some of your thoughts thx




Did you ever get to the bottom of this? Just stumbled across your site while searching for something else and thought i’drop have a look.

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