Extreme skin loss on koi, what is this??? Help!!!!!

[SanfordLopez]

Hello everyone I have a koi that I noticed was swimming funny about 2 months ago or maybe even longer. About a month ago the fish kept breaching then just went to bottom of the pond. Fish spends most of the time at bottom of pond by itself. I finally took it out to see what may be going on and I couldn’t believe what I saw. I immediately put the fish in a clove oil solution to put it down. But I would like to know what this is. I checked all my other fish and they seem normal and are swimming and eating as usual. Should I be concerned for my other fish? I've had the pond for about 10 years with no real changes. The fish that I put down has been in the pond for about 3 or 4 years. I can't even believe the poor thing was still alive in this condition.


Water parameters
Ammonia=0
Nitrite=0
PH-8.2
KH=125
Nitrate=20
I do approx 20% water change weekly and add Vanish, baking soda and Prime.
Pond size is about 6 feet by 8 feet and 3 feet deep.
Water temp is 60

[RichToyBox]

What you are looking at is referred to as a major ulcer. The cause is generally bacteria entering the fish through parasite bites/punctures of the skin and then the bacterial infection rages on. The fish resting on the bottom of the pond, scraping against grit that has made it into the pond accelerates the erosion of the skin. Most of the major ulcers that I have seen have been on the belly of the fish, as is yours. Being down there, they are not easily visible until they have gone large.

You mentioned the breaching, and that is a classical sign of parasite attack, and would be a good reason for having a microscope to identify the parasites attacking the fish and begin treatment before it gets too bad. I am glad you provided test results which to me means you are trying to maintain a good environment for the fish.

Could this fish have been saved???? Maybe, but it would have taken a lot of effort, a separate isolation tank and months, so I think you did the right thing.

[*Ci*]

So sorry for your loss, and I agree that euthanasia was the best choice. Amazinf that this fish still lived in this condition! I am curious about this area (circled). Do you still have the body? Care to try your hand at an autopsy? It is a great learning tool, if you are not too squeamish.
My guess is a tumour and I wonder if it broke through the skin to cause the start of the ulcer.

[SanfordLopez]

Thanks so much for the help. I already buried it in my yard. I only hope my other fish remain healthy.

[SanfordLopez]

Without me knowing what type of parasites the fish might have, what would be a good product to treat the rest of fish? On a side note. I do have salt in the pond. It's at .15

[kdh]

There is no need to treat your pond for parasites if the other fish show no symptoms.

[SanfordLopez]

Thank you very much for the info. I appreciate it.