Common Aquarium Fish Diseases

Blue Tang in reef tank

The following should only be used as a guide for the identification of potential fish diseases. If you have a problem related to fish disease in your aquarium, it is best to consult your local fish store for a diagnosis and possible treatment.

Acidosis/Akalosis Symptoms:

Fish shows an excess of mucous, the skin becomes inflamed and the gills may bleed and deteriorate. Fish may also display darting movement and may jump in an attempt to leave the water. Fish also shows signs of increased respiration and can be seen gasping for air at the water surface.

Fluctuating pH values causes this problem. Most fish can tolerate a pH between 6.0 and 8.0. If the pH drops below 6.0 skin problems – acidosis – may develop. A pH above 8.0 on the other hand can cause the erosion of skin and gills.

An immediate water change is recommended. If the pH remains unchanged, check with your fish store. There are several products on the market that can either raise or lower your pH. If the pH fluctuates frequently, you should take routine measurements to assure a balance which your fish can tolerate.

Bacteriosis Pinnerum (Fin Rot) Symptoms:

Fin rot begins with a slight discoloration of the edges of the fins, making an early detection difficult. As the disease progresses, the fins begin to fray. The deterioration continues, resulting in only remains of the fins, once the disease is in it’s terminal stage.

Several bacteria cause Fin Rot, namely “Pseudomonas Flourescens”, “Aeromonas Sp”. and “Haemophilus Piscium”.

Fin Rot is considered difficult to treat. It is recommended to consult with your local fish store about the correct diagnosis as well as a possible treatment.

Infectious Dropsy Symptoms:

Typical dropsy has several symptoms: bulging eyes, regressing eyes, pale gills, inflamed anus. In some cases the belly may be inflated, red spots can be seen on the skin, as well as damage to the fins.

This disease is caused by a pathogen on which researches cannot agree. It is widely believed that 2 bacteria causes dropsy, namely “Aeromonas Punctata” and “Pseudomonas Flourescens”.

Like Ich, dropsy is extremely infectious. Fish are mainly receptive to dropsy if they have been weakened by stressful conditions caused by poor water conditions or another disease. Treatment is difficult, therefore prevention is key. Good maintenance of the water conditions as well as early detection and treatment of other diseases is a good measure. If a fish is diagnosed with dropsy, the ailing fish should be immediately removed and euthanized.

Gas Bubble Disease Symptoms:

Bubbles/blisters can be found beneath the skin and inside the body. They are mostly found around the head and the eyes.

A condition known as “over saturation” is created due to the dissolving of excess amounts of gas. A certain amount of gas is always dissolved in liquid in relationship to such factors as pressure and temperature. When these gas levels are to high, the water will constantly attempt to release the gas in the form of small bubbles. Too much sun and the heavy plant and algae growth associated with this is a common cause of over saturation. Since the plants take up and release a lot of oxygen, the fishes’ blood can itself become over saturated.

Reduce the amount of sun light the aquarium is exposed to. Further, an air stone can help prevent problems.

Ichthyophthirius (ICH) Symptoms:

The entire body of the fish including the fins and gills are effected. White spots can be seen with the bare eye. The appearance of these spots is often compared to salt grains. Eventually the skin will get slimy and the fish will rub its body against rocks and decorations. The fish will close its fins, get thinner and less and less active.

Ich is caused by an organism called “Ichthyophthirius multifiliis”. The life span of this parasite consists of three stages. 1. Growth – The organisms attach to the fishes’ skin. 2. Cyst – After dropping to the bottom of the tank the organisms divide while protected by a gelatin-like covering. 3. Infectious – The divided spores seek for a new host.

Ich is a highly infectious disease and should be treated immediately. If Ich is detected, it is best to treat the entire aquarium due to its highly infectious nature (vs. treating individual fish in a hospital tank). There are many different products and your local fish store should be able to help you with the recommendation of a medication as well as treatment instructions.

Lack of Oxygen Symptoms:

Increased respiration, open gills, lose of color, gasping for air (often at the water surface), fish appear restless.

Excessive decaying matter such as food, dead plant matter which utilizes oxygen during the decaying process, nocturnal respiration of plants, and high water temperature at which less oxygen is dissolved in the water.

Aeration of the water is immediately required to avoid fish from dying from suffocation. A common misconception is that an airstone will provide adequate oxygen to the water. In reality, the best source of oxygen is provided by a good filter, which allows oxygen to be dissolved through surface turbidity during the return of the water to the tank. Further a good balance of plants will help stabilize the oxygen levels. Last but not least, all decaying plant matter, foods and algae should be removed from the aquarium.

If the problem is serious, an immediate water change should be done. Adding fresh water will significantly increase oxygen levels.

Leave a Reply

14 Comment threads
10 Thread replies
Most reacted comment
Hottest comment thread
16 Comment authors
Notify of

Hello! I was hoping you might be able to provide some suggestions for treating my sick goldfish. We have a 20 gallon tank with one goldfish. We do regular water changes and we test the water each time. Four days ago, we noticed our goldfish was spending more time at the bottom of the tank. He was still somewhat active, but his swimming was sporadic and brief. That same day, we saw his feces was long and white with what appeared to be air bubbles. We tested the water and had perfect readings, so we suspected that he was constipated.… Read more »


Hello Kim, we don’t diagnose via email, but I would recommend reading up on swim bladder disease. Goldfish are prone to that issue.


Hi I need help I don’t know what to do I’m just beginning my aquarium of been doing good for a year bit I got some new fish now all my fish are either sick or dying I don’t know what to do or who to go to

There’s not a whole lot of information here. Please use our guide above to review symptoms to help identify specific fish diseases. Your best bet in a case like this is to speak to a knowledgeable fish store employee, in order to diagnose and find an appropriate treatment.They should not only be able to help with diagnosis but should also have products for treatment available.


This was really well written article of fish disease and their symptoms and treatments. I enjoyed reading your article. I like the way you wrote about disease in detail. Thanks for sharing the article with us. My goldfish suffered from fin rot disease month ago and I read your article. and when i corrected my water parameter the disease was gone. did 30% water change every week until he recovered. turned out, the worst thing you do to your pet fish is fail to give the water parameter that you fish requires. I learned my lesson.
Thanks for your help.


Hi, we have big garden pond. It has catfish, gurami, gold fish, gappi. Yesterday 4 big cat fish died. Today 2 big gold fish are about to die. We noticed fish keeps there mouth open and swimming on top lifeless. They keep mouth open. Also we noticed died cat fish yesterday had mouth wounded.
Kindly advice what needs to be done to save my fish.


There is too little to go by. You will need to test the water and see if this provides any clues. See if there are similarities and watch the fish for odd behavior. All these clues should get you into a direction to diagnose the problem.


I’m new to this…I don’t know what hat wrong with my glofish it has what looks like clear bubbles on only it’s fins…Can anyone tell me what this is and can and how can I treat it??

This sounds like it may be Gas Bubble Disease. Although, the bubbles are usually most visible on the head of fish. Your best option is to speak to someone at a fish store with knowledgable staff. Explain the symptoms and they should be able to recommend a treatment option. The above article is intended as a starting point to diagnose potential disease. Trying to make a definitive determination in the comments section is usually not the best option. Good luck! I hope it works out.

Khaled Selwaiea

my guppy fish is swimming head up on the surface and it feels weak. Also the stomach somehow became black and so did the eyes. I dont know whats the problem and what needs to be done. Can you guys help me here?


It could be ammonia poisoning or myxobacteriosis. Both can be fixed, but please read up on both to determine if either option matches the symptoms. We generally refrain from diagnosing, so take it as a lead. Both are actually caused by overfeeding, or overstocking, stress and less optimal maintenance. Address these aspects as well to help the fish heal and to prevent any further issues.


My fish has an inflamed belly and it keeps floating near the surface involuntarily. It shows no discolouration and patches and its fins and gills look fine. What might it be? overfeeding or something?


Most important part is to maintain a good environment for the fish. Then I would recommend to read up on swim bladder disorder. It could be caused by bacteria or stress. In most cases it is not a disease but a symptom.
As you read up on the issue to find the appropriate treatment, increase or lower the temperature to 80 degrees and stop feeding the fish for a few days. Then feed peeled peas. In case it is bacterial, you should use an antibiotic.


my achilles tang has been doing well and eating alot then overnight during the day she is very pale and stuck at the bottom and is gasping for breath and can not proproly swim, i need help!

Nevin, our article here is to give an overview of common disease symptoms. We hesitate to try to diagnose a specific disease over our commenting section. It’s best to seek the advice of knowledgable fish store staff, who also sell medications to treat the various diseases. Please seek in-person advise asap.


hello my fish has reddish lines in random spots of its body which appear to be blood but its not bleeding and its eyes are cloudy we have been treating him for cloudy eye but while his eyes are improving his state doesnt seem to be. he is just floating and every now and then he turn vertically but brings himself back down and sometimes he swims but not very often its been happening for like a week now and im worried


Some of these issues are symptoms of poor water quality. Improving the water quality will also improve your fish health. Check on ammonia, ammonia poisoning shows by fish behaving sluggish, hovering near the bottom, inflamed gills, no appetite. Feed the fish 1-2 cooked and peeled pees per day. It does wonders for swim bladder issues.


Hi, I’m having problems with my fish recently. My fish are darting around and sometimes flicking against the bog wood or sand, I understand this is called ‘flashing’. I’ve had 3 guppies die over the last week but I this may just be due to age (bought them last September and they were fully grown adults then). Today I’ve just seen another fish which seems quite lifeless at the bottom of the tank and hiding. He’s not even coming to the top to eat. There’s no white spots so can’t be ich. Although the fish that seems to be suffering… Read more »

James Browne

Hi, my goldfish has been off its food for several weeks now and lays on the bottom of the tank. Every now and then it will swim to the surface and then resume its position on the bottom, it lets out bubbles during this. I thought it may be bubble disease but doesn’t have any bubbles on itself. I have another goldfish in the same tank which is fine. Can you help?


These definitely are not good signs, but too inconclusive for a diagnosis. Besides we are hesitant to diagnose via email, unless it is quite obvious. We recommend to consult goldfish disease websites or your veterinarian.


My brislenoise catfish is covered in what looks to be air bubbles , I have just done a water change. Any advice would be great as I’m worried.

This sounds like Gas Bubble Disease. Please visit to your local fish store and describe the symptoms. They should have treatment options for you to consider.


Helped alot thank you

Abdul Auwal mahdi

Thank you so much i find your write-up educative

Click to Hide Advanced Floating Content
Cart Menu Button Image0
Your Cart