A Closer Look at Black Spot Disease – Part 1 (Ammonia)

There are two very different fish diseases that get called ‘black spot disease.’  One is caused by healing after injury (most commonly ammonia burn), and the other is caused by a parasite that infects the intestine of birds.

Ammonia burn

Most examples of black spot disease in aquariums are the result of ammonia burn on the fish’s skin or fins.  When the affected areas start to heal, the small patches that recieved the harshest burn turn a dark brown or black colour.

The black spots themselves appear as discoloration of the skin, rather than something in or on the skin.  They can range in size from barely noticeable to a “rolled around in black paint” look, but are usually small smudges.

Blackened skin from ammonia burn is actually a good sign.  It means the ammonia has dropped back to a safe level, and the fish’s skin has started to heal.

However, it is a worrying sign that the ammonia level was raised in the first place.  Action needs to be taken to minimize the risk of raised ammonia.  A lot of fish that suffer ammonia burn don’t get the chance to get black patches on their skin.  They get killed instead.

Spot the signs

Fish in a tank or pond with high levels of ammonia will gasp for oxygen at the surface, float on their sides, sit at the bottom, lose their appetite, get red streaks in their fins, develop reddening around the gills, and/or make swimming look like hard work.

As soon as any of these behaviours are spotted, get the water tested to confirm ammonia poisoning and take action to remove it.

Removing ammonia

Changing the water is the best way to get rid of ammonia.  Do it every day until the ammonia levels are down to an acceptable level i.e. less than 4 parts per million.  An ideal level is less than 2 parts per million.

The other option is to use chemical treatment, but water changes are obviously better as they do not involve adding further chemicals to the water.


Test the water regularly, and change it regularly.  High ammonia levels are a sign of a badly managed aquarium.

Do not overstock.  Too many fish produce too much waste, which contains ammonia.  If the filter can’t cope, ammonia poisoning is inevitable.

Do not overfeed.  Uneaten food decays, producing ammonia.

Use a treatment tank if the water needs to be medicated.  Medications for unrelated fish diseases can kill the bacteria in the filter that remove ammonia from the water.

Keep a very close eye on new tanks.  Ammonia poisoning occurs most often in new tanks.  Ammonia will peak at the end of the first week.  It is advisable to start with only one fish so waste is kept to a minimum.

Related articles

Choosing and Aquarium Filter

Goldfish Aquarium Water Testing

Changing the Aquarium Water

22 Responses to “A Closer Look at Black Spot Disease – Part 1 (Ammonia)”

  1. Bamboo Avenger Says:

    This is a great article that should be promoted much more. Unfortunately, this characteristic of goldfish is not well known to people and surprisingly a large amount pet store keepers.

  2. julia Says:

    I did have high ammonia and did a water change as well as treat for ammonia. One week later, my weakest goldfish (purchased over one year ago as a tiny feeder fish) has the black symptoms and is lying upside down and struggling to breath.

    Is there anything to save this fish? I separated him into a bowl and addes some stresscoat. What should I do to save him?

  3. kat Says:

    i have two goldfish, one of them is new, the other i have had for one year, i put them in the same water thing after making sure my new fish was not sick by keeping them seperate for a week.
    Now my first goldfish(after they have been in the same tank for like, two weeks)is kinda fat by her abdomine(pregnant maybe?)
    and she was just orange and white
    then the other fish , the new one, stared getting kinda dark under its left front flipper thingy
    now its black on all its tails\flippers, and it almost looks like its black from the inside
    im scared that my fish might both die cuz in less than two hours my old fish has gotten a black spot on its tail fin
    and when i woke yesterday morning they were both bleeding, even tho i am feeding them regularly
    they were both bleeding on their mouths and my new one (whose name is King)is bleeding under its mouth and under one of its from fins
    please please email some kind of info at katluvr12@gmail.com
    please tell me any suggestions u might have cuz im desperate

  4. Amanda Smith Says:

    Are there any goldfish diseases surrounded an eye of the fish. My goldfish che-che has one black eye and the other is normal. This happened about a week ago, and I dont know what caused this to have happened. Can you please, let know me know if theres info about this and I how I can get him well again. Thank you so much. Amanda

  5. stephen Says:

    hi my fish was yellow but now he is half black someone help me

  6. Abhishek Says:

    i have two goldfish. They both have red color lines(seem as if blood has come under the topmost layer of skin in the form of lines and not spot) around there mouth. The smaller one is the first one to have it around its mouth. The other has got only on one side.
    Plz help and suggest some measure.

  7. Graham Robinson Says:

    My 5 year old goldish has deveoped a black top lip, like a mousetach, otherwise it seems very healthy, can any one tell me what this is please.
    Best Regards,

  8. bill Says:

    this atrical is very helpful i was looking up goldfish diseasea for my
    mother when i ran across this one it explaned everything i needed to know..
    thank you and keep up the great work..

  9. Sarah Says:

    after noticing my goldfish acting very strange, 1 flipped itself out of the tank and 1 buried its head into a rock, i had no idea why it seemed my fish were trying to commit suicide!! they looked very poorly, frayed up fins and some lying still at the bottom.. i searched the net and after reading your write up, i discovered that my aquarium had high ammonia levels which was burning the fishs fins and hurting them so much that they were trying to free themselves from the polluted water!! immediately after reading this, i did a full water change, bought a new larger filter adequate for the tank size and even purchased a plant as i figured it would allow more oxygen to enter the water.. one week later and thank goodness they look better!! the fish with the most damage, its fins have now turned black, a positive sign of healing and they are all eating well and remain active.. i am now keeping a close eye on them all and am going to invest in an ammonia tester and an aquarium vacuum which cleans the gravel as i now know the high ammonia levels were caused from build up of the fishs waste.. i cant thank you enough.. if people were more clued up on how to look after fish, when they are purchased from stores it may put a stop to alot of pain and suffering the fish have had to encounter x x

  10. Grace Says:

    my fish has black spots in between the scales and is staying at the back of the pond, not eating and not coming up to the surface! i have seven other fish in the same pond. is that to many or what shall i do? thank you very much!

  11. lisa Says:

    My 5 year old goldish has deveoped a black top lip,and it not doing much

  12. Marika Says:

    My fish have what they talk about in the article. But one keeps turning on it’s back for a bit and then it turns it’s self over. Can we help them anymore than what we are doing?

  13. Catherine Says:

    My little white goldfish has every now and then formed another little black spot on its scales or fins. We’ve changed the water, though not often enough because we are harldy home.

    This article explain a lot, however, my little fish is acting so poorly, sitting at the bottom of its bowl and only moving when we lightly tap on the bottom. 🙁 Is it too late to do something to save it?

  14. Lil Says:

    One of my fish died and my second fish is starting to get black dots on its head. what can I do? I’ve already washed the bowl a couple times.

  15. Nicole Says:

    My 5 year old won two goldfish at the county fair. We’ve not had fish in years so only had a bowl to put them in. We were doing regular water changes, but after a long weekend away, we returned to find one goldfish dead and one looking pretty unhealthy. After searching, I found this forum, determined it was ammonia in the water so I picked up an aquarium kit with filtration etc and the remaining goldfish has made what seems to be a remarkable recovery. He sitill has some black on his skin and fins but eats well and behaves normally. Thanks to all who contributed info here.

  16. linda Says:

    I’ve been surfing all over the web for black spots symptons,although many mention black spots,no one explains what causes it and how to deal with it………….thanks guys….now my nemo has a chance to live a healthier life.

  17. Lu Says:

    It’s sad watching fish suffer from black spots. Maybe the reason why they don’t mention how to heel fish from it is, because there is no cure. 🙁 Perhaps it’s too late. D’;

    On the other hand… it could be that some fish survive through it, and some don’t. Depending on how they heel.

  18. nicole Says:

    one of my fishes died of ammonia poisoning and i feel awfull because it was a simple thing to help him but he also died of fin rot, my other fish who is still alive never really got sick but now i change the water and my fish has three black dots on him is the poisoning healing??? or is it another diesase??

  19. ben Says:

    I adopted some fish from a friend who had 4 very large goldfish crammed in a ten gallon tank. I put them in a 55 gallon and they seem much happier the first couple days now there dorsal fins are down and black is appearing on the tips of there tail fins and front fins. I have no idea if I’ve done something wrong or if there healing from the other tank issue.

  20. lulu Says:

    My three goldfish are thirteen years old. I have owned them for three years. They are resuce GF. One fish has developed a blackish smudge on one side. After reading this article I think Chloe has some amonia damge although for three years I have never had a problem in the tank. Chloe was swimming on her side a little too. I am going to get a water tester; I have never tested the water. I change it over by 2/3rds every week with well water that sets till the temp matches the tank, and have never had a problem. I feel so bad. I do hope this is the problem ’cause it is the easiest to remedy. I really don’t like to think that Chloe has parasites.
    peace to all

  21. ashley Says:

    i have 2 gold fish, and 1 of my goldfish has developed a small, black line on 2 of her fins. I’m not sure if she is healing from something or is suffering from some sort of disease. I’m not sure if she has parasites or if it’s something else. The other fish is doing fine, so i’m sure it’s not that the water temp is too high or to low. it’s probably not the Black Spot disease, but it could be, just in a different form of it. 🙁

  22. Shoefits Says:

    6″ 3 y/o comet goldfish was exposed to high ammonia during salt treatment of tank for ich. After treatment, ich gone but fish developed black splotches (not dots) on body and black tints to end of fins and tail. Also black smudgy marks around the inside of the eyes. Seems to be listing on one side or the other and is somewhat sluggish. Doing regular water changes seems to have helped, but fish still seems very sensitive to the aquarium light. Very strange. Ideas? Thank you for this article.

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