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The Goldfish Sanctuary

Black Smudge

What follows is a description of an unknown disease we have nicknamed "black smudge." We have received various mail at the Goldfish Sanctuary with questions about this condition. Very little information is available at this time, but here is the information we have, and a possible way to treat it. Remember to isolate any infected fish, and also remember that sometimes, treatment will have to be repeated in order to fully clear the condition.


I saw a post on the rec.aquaria.freshwater.goldfish newsgroup quite recently about black smudges on goldfish. It said that the black smudges were the result of scarring due to ammonia burns. I have a pair of fantails who also got black charcoal-like smudges on their bodies and fin edges during tank cycling, when the ammonia and nitrite levels got out of control. They recovered without medication after a couple of weeks of changing a third of the tank water every day until the tank had cycled.

Here's a copy of the message:

Subject: Re: Black spot on my goldfish
Date: Tue, 29 Apr 1997 11:51:56 -0700

+One of my fantail goldfish has developed a black spot on top just in
+front of its top fin. No bumps, just a black spot. Recently switched
+to a higher protein content flake food. Is that causing the spot? Or
+does my fish have a fungus? Is there any kind of treatment for this?
+I've a 10 gallon tank that has 2 goldfish and a hest snail.

Black spots are usually scabs over areas that are healing. Your fish could have scraped itself on something sharp in the tank, or if you have a new tank, it may be recovering from ammonia burns or some other water quality problem during cycling.

Rarely, the black spot could be a disease passed on by snails if the snail has been exposed to bird droppings (as in an outside pond) and is still in the first generation.


One of our goldfish has begun showing signs of discoloration... his fins have blackish areas, and a black spot has just appeared near its mouth. For a long time, we noticed blackish areas surrounding his eyes, but thought that to be just his coloration. Our local pet store doesn't seem to understand, but I think there's something wrong. The other two goldfish seem fine. Do you have any suggestions on where to look for more information, or perhaps a solution?


We had black spots on one of our three goldfish... and everyone thought that it was a color change ... so we let it go until a blackspot started showing up on the dorsal fin of one of the other goldfish (the first fish was quite black ... like it had rolled around on a oil spill!). MESSAGE 4 I was fortunate to find your article of the disease you nicked named "Black Smudge." I tried everything under the sun for my poor Goldfish and nothing was working. I, too, had problems trying to find somebody who knew what I was talking about. They never heard of black marks on fish. You should hear some of the reasons they came up with for black marks on fish but that's another story. Here is the scenario and the events that followed in a 2 month span. The 3 goldfish are 1 year old Fantails. They lived in a ten gallon tank for 9 months without any problems with fungus or disease. I bought them a new home (30 gal. tank). That's when the problems started. New tank cycle was started and fish were doing fine. The second week they developed Ich. I medicated them and cured it with Maracide and salt. The Ammonia levels where high so I did frequent water changes. The smallest fish started with a white blister looking thing at the beginning of her tail fin. All the fish were showing signs of red streaks in the fins (hemorrhaging). I moved them to the 10 gal tank and medicated them with Oxolium. No sign of improvement. Cleaned the tank (10 gal) and waited a week. Introduced a new medicine Maracyn-Two. No improvement. The black marks kept getting worse and the hemorrhaging had stopped. I decided to start over with the 30 gal tank and clean everything so the Ich wouldn't come back. I also decided to go back to the BASICS and stop ALL medications. I put the fish back into the big tank with clean chlorine free water. No medicine, No salt. I ran my bio filter (Emperor 280) on full flow and the U.G. Filter at full flow. Installed Zeolite ammonia cartridges on my air tubes and also put it in my filters along with the normal amount of Charcoal. I performed 23 % water changes every other day during the cycle. FINALLY there was some improvement. In conclusion, it seems that the black smudges or marks on the fish were caused initially by ammonia burn. Medications didn't help in my case but keeping my water quality at an OPTIMUM did help. When all else fails, go back to the basics !! It costs less too :-) If anybody runs into this problem, I hope this helps. It drove me nuts for awhile. Good luck to all. MESSAGE 5 I have the "black smudge" problem with my two fantail goldfish, and despite water changes and keeping the ammonia level down, the smudges seem to be spreading and getting worse! My fish are only about 2-3 years old and I want them to live, but it seems that no matter what I do- they are getting sicker and sicker. I have followed the suggestions that you have posted, but if there are any other suggestions that you have that will help me keep my fish alive- I would greatly appreciate them. They are full grown, and they live in a 20 gallon tank with one small filter, and one heavy duty filter, as well as a long airstone. I have been using "ammo-lock", "stress coat" and Tetra's "aqua safe" to try and neutralize the ammonia, as well as an "aqua clear- amrid ammonia remover" in conjunction with my carbon filter.