The 10 most common diseases in aquarium fish


Neon Fish The best method of prevention is the methodical and periodic control of water conditions. Spend time observing your aquarium. Look closely at all the fish and their behavior. Verify that the skin, scales and fins are healthy. If there are constant fights between some of the fish, ask for advice, they may be incompatible to share the habitat.

Always have products to treat white spot, it is the most common disease. Also have among its elements a bactericide and a fungicide. These products are usually common to many diseases. Keep in mind your expiration dates.

Take precautions when introducing new fish, rocks or plants, especially if they come from natural environments. Click here To know which rocks are suitable for the aquarium and which are not, you will also see the consequences derived. Below you will find a complete disease guide. In it you will get information about the symptoms, how to identify them, the probable causes and the treatments to follow to try to heal the affected fish.

Treatments of tropical fish diseases

The specific treatments for each disease are detailed in the guide below. But there are certain details and facts that you must understand and respect in every treatment. The first fundamental resource is the patience. The treatments usually last a few days, sometimes weeks. Always follow the instructions of the specialist who supplies the products necessary to treat the fish or the aquarium. Also understand that if a treatment begins and the improvement does not come within a couple of days, you should not suspend, modify or replace it. That mixture of products can lead to even more severe disorders of the fish.

Sometimes the right chemicals for a disease can negatively affect other elements, such as plants or bacteria. Get advice to avoid extra problems. Always have items to build an aquarium for quarantine in emergencies. Below the disease guide you will find tips for the assembly of the quarantine aquarium.

White Point

Symptom: The body of the fish is covered with small white dots. Also its fins. In a couple of days the points will increase and other fish will be infected. Their gills do not move naturally. Causes: under the skin of the fish there is a parasite called Ichthyopjirius . This parasite reproduces leaving the body. When it does, it leaves a hole in the skin that quickly becomes infected. A cyst will appear that bursts shortly. From there come young parasites. White spot is the most common disease in aquariums. Treatment: specialized stores sell chemical products to treat it in the first phase only. If you have a filter in the aquarium, do not desactivate it. Just remove the activated charcoal.

Lernaea worm

Symptom: You will notice that the fish swims from side to side, rubbing its body against rocks and plants. You will notice inflammations in the skin, and there are threads that look like worms. These organisms arise upwards and are light green. Causes: it is the parasite called Lernaea. He buries his head in the body of the fish, being anchored to him. Treatment: Move infected fish to a quarantine aquarium. Use a small clamp to remove the worms. Be careful, you should not cut the worm, because if your head is buried in the fish, everything will remain the same. If the fish is badly injured, apply appropriate antiseptics. In specialized stores acquire Metriponate and supply 1.5 mg every 4.5 liters of water.

Slime on the skin

Symptom: You will notice that the fish that suffers from this disease will look dull. Your body is covered by a thin layer of grayish and whitish mucosa. It also affects the gills. The fish rubs its body against rocks and plants. Causes: The main cause is severe neglect of water conditions. The consequence is the degradation of the natural mucus of the fish. It is then exposed to parasites such as Chilodonella and Ichthyobodo. Treatment: It is really difficult to treat this disease, especially if it advanced too much. If the gills of the fish are healthy, go to a specialized store to supply the indicated product. If the gills are already damaged, ask a specialist to treat the fish in a quarantine aquarium with formalin.


Symptom: the abdomen swells so much that the scales protrude from the pointed body. Hydrops is chronic. It appears in sight once advanced and develops in the long term. Causes: Although it may be due to a completely inadequate diet, the main cause is severe neglect of water conditions. There is usually a high level of nitrites and sodium chloride. There may be too many bacteria. There is also fish organ dysfunction. Treatment: there's no cure. Study the ideal eating habits and water conditions for the fish species you select.


Symptom: the fish looks agitated, breathing demands a lot of effort. The color may darken and your eyes become glassy. The gills become inflamed if the picture is severe. Since little oxygen reaches your brain, it moves awkwardly. It also rubs its operculums against the rocks. Causes: gill membranes become infected with virtually no visible parasites. Treatment: specialized stores sell products such as Sterazin. The treatment can be quite long. Sometimes you have to be patient until the eggs of Dactylogyrus hatch.


Symptom: The fish's body seems to be covered with a velvety and yellowish film. It also covers the fins. The fish is agitated by breathing difficulties, and rubs its body against the rocks for relief. Causes: called parasites appear piscinoodinium. They take root in the skin of the fish to feed on them. Treatment: The first step is to cover the fish tank and leave it without light. This will weaken the parasite. Specialty stores sell chemicals to treat it. If you have a filter in the aquarium, do not desactivate it. Only remove activated carbon so that it does not remove the chemical from the water.

Symptom: sectors of the fish's body are covered with villi that look like cotton flakes. The affected sectors owe this to the damage of the natural protective mucosa of the fish. Causes: It may appear after white spot disease. Sometimes it is a consequence of severe neglect of water conditions. It is common for fungal infection to happen to a wound on the body or fins. Treatment: specialized stores sell fungicides, which must be applied to the entire aquarium. If you have a filter in the aquarium, do not desactivate it. Just remove the activated charcoal. Get advice to detect the causes of the outbreak and improve conditions afterwards. If the fish had wounds, verify that the species in your aquarium are suitable for living together.


Symptom: The belly bulges noticeably. Being constipated, it does not feed or defecate. Rest on the substrate for many hours, since it is weakened. It can be difficult to distinguish this disease from dropsy. Causes: In most cases it is due to overfeeding. It can also be an incomplete or inappropriate diet for your fish. Treatment: Add half a teaspoon of magnesium sulfate tea to the aquarium water every five liters of water. If the fish recover, get advice on the eating habits of your fish species.


Symptom: the fish thins and its eyes protrude from its orbits. Causes: This disease, distinguished by inflamed nodules behind the fish's eyes, is usually the result of bacterial sepsis or tuberculosis. A severe neglect of water conditions is generally observed. Treatment: improve habitat quality. The treatment process is slow. If they do not recover, it is because the origin of the disease is tuberculosis. This last case has no cure. There is no alternative but to eliminate infected fish.

Lice (argulus)

Symptom: The fish rubs its body against the rocks for relief. Tiny parasites grouped in the form of flat discs appear on your skin. Causes: The lice have suckers that adhere them to the body of the fish. They penetrate it to feed on their blood and lay eggs. Then they will look for other fish to continue feeding. Treatment: Move infected fish to a quarantine aquarium. Use a small clamp to remove the parasites. Apply suitable antiseptics for fish wounds. In specialized stores, purchase Metriponate and supply the main aquarium with 1.5 mg every 4.5 liters of water. Buy also a chemical to kill larvae.

Intestinal parasites

Symptom: You will notice that fish that eat abundantly lose weight. Sometimes they bring parasites from their habitat in the wild. Parasites can be seen coming out the anus. Causes: Some intestinal worms enter the body of the fish and feed on their blood. Treatment: Request assistance in a specialized store. You will probably be given a anthelmintic to include with food. Apply a suggested chemical to remove parasites from the aquarium.

Damaged fins

Symptom: Fish with highly developed fins are very prone to this disease. Catfish and mustache species too. Swelling of the fin rays is observed. Subsequently, the fins are shortened and deflected. Causes: This disease is due to bacterial infections due to severe neglect of water conditions. Other fish may also be biting the fins of the affected fish. Treatment: improve habitat quality, both water and fish. Transfer the fish to the quarantine aquarium and treat it with Myxazin bactericide. You can also choose to use gentian violet. Consult a specialist to advise you on the dosage of the products.


Symptom: It usually affects the Discus. The sensory pores in the head are filled with pus. Also the sensory pores near the lateral line. Another indicator is long and hard stool. Causes: the cichlids and some anabantids (or labyrinthids) harbor a parasite called Hexamite. It is harmless until the fish has a loss of its natural defenses. Treatment: Request assistance in a specialized store. They will probably supply you Dimetronidazole. Apply 100 mg every 9 liters of water in the aquarium. The correct procedure is to extract a couple of liters of the aquarium, incorporate the total dose for the aquarium and, once diluted, incorporate the product already diluted in the aquarium.


Symptom: The fish rubs its body against the rocks for relief. Tiny worms appear on your skin. It is a very contagious disease. Causes: leeches can reach the aquarium inside a new fish. Their eggs can arrive on rocks brought from nature. Leeches have suckers that adhere to the body of the fish. Treatment: Move infected fish to a quarantine aquarium. Use a small clamp to remove leeches. Apply suitable antiseptics for fish wounds. In specialized stores, purchase Metriponate and supply the main aquarium with 1.5 mg every 4.5 liters of water.

Swimming bladder disease

Symptom: the affected fish will swim upside down, inverted. It does not move naturally, it seems clumsy and it hits itself with the objects that surround it. Causes: This disease is due to bacterial infections due to severe neglect of water conditions. It can also be a congenital problem. Treatment: It is unlikely that we will identify exactly the origin of the disease. improve habitat quality, especially water. Move the fish to the quarantine aquarium. Request the appropriate chemical in a specialized store and apply it both in the main aquarium and in the quarantine. Wait a week, if the affected fish does not improve, it probably will not do so later. There will be nothing left but to sacrifice the animal.

Quarantine Aquarium

A 12-liter fish tank will be suitable (30x20x20 cm). Do not use bottom plates, a thin layer of red gravel will suffice. Include an artificial plant and some rock for shelter. Do not decorate the aquarium, for obvious hygiene issues. Place a small sponge filter and a heater (provided it is tropical fish).

The water to be used is the same as the main aquarium. If the fish is sick, what it will least need will be a change in water conditions. Your defenses may not tolerate it. It is important that this aquarium is dark, will take away energy from parasites.

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Related topics

One of the main reasons is to neglect the filters assuming a great danger. Many times the contact with toxic matter How nicotine can cause problems. Another related but not so frequent thing has to do with the excess oxygen in water that would cause cardiac embolism.

It is mainly due to the absence of dissolved oxygen in the water. The fish's symptoms are that they swim across the surface looking for the most superficial layer of air, although they usually do so without obtaining results. The only solution to this problem is to decrease the number of fish of the aquarium, and on the other hand the aquarium aeration system should be checked.

3. Temperature changes

It usually occurs when there is a sudden change in temperature, and the symptoms that fish present are that they gasp on the surface, they swim quite nervously They try to be near the water heater where the most abrupt changes occur while waiting for their body temperature to stabilize.

The solution to these types of problems is to make an aquarium water change and ensure that the water is found with the same temperature. On the other hand, we should try not to place the aquarium where there are drafts. Depending on whether it is a fresh or salt water aquarium, the temperature varies quite a lot.

4. Viruses and bacteria

Sometimes the aquarium is not clean enough and can wreak havoc on the life of the fish. On the other hand, when he dies a fish or other being in the water, you must try to remove your remains as soon as possible so as not to contaminate it. The most common disease is dropsy, especially bacterial fin rot.

5. Chlorine poisoning

The cause comes directly from the chlorine of the water and the symptoms that fish present are the destruction of the gills, discoloration and pale skin, sunken eyes, loss of coordination when swimming and spasms.

To remedy these consequences, the easiest thing to do is try to remove the chlorine from the water before making the water changes using specific products or letting the water stand for at least 24 hours.

Most common freshwater fish diseases

Most of the cold water fish diseases, They are common to tropical fish diseases, although some, due to water temperature, may develop better or worse.
The most common diseases in aquarium fish are produced by:


6. Tuberculisis

Sounds weird, but in the marine world it also exists. The fish carrying the germ are the only source of infection. on the other hand, the infection is transmitted by ingestion of material infected. The symptoms that appear are slow movements, thinning, paleness of the colors, falling scales, ulcers and deformations of the jaws and also of the spine.

10. Branchymycosis

It is produced by the fungi Branchiomicosis sanguinis and Branchiomicosis demigrans. This disease is also known like that of the gill rot. This disease is especially common in waters that have a lot of organic matter, with algae and temperatures above 20 degrees. One of the most common symptoms is lack of appetite or suffocation. At first glance the gills look very whitish.

1.- Rot of the fin

Fin rot is one of the common diseases of aquarium fish. It is also one of the common diseases of fish more treatable and preventable.

The fins become white, opaque, appear inflamed, frayed and they can even bleed. If the erosion of the fin continues to the base, the disease could become fatal.

EnvironmentalWhen the fish do not look healthy, damage to the fin has already occurred. Factors such as: overpopulation, pinch of the fins, poor water quality and poor food quality They can contribute to the cause of fin rot.


You can use antibacterial medications available. Also make water changes and add aquarium salt will help you. The drugs chloramphenicol, oxytetracycline Y tetracycline They are good options to help cure fin rot.

2.- Swim bladder disorder

Swim bladder disorder It is most commonly seen in Bettas and Goldfish But it can occur in any species of fish. When a fish has a swim bladder disorder, the swim bladder does not work normally due to physical defects or illness. Things that affect the bladder contribute specifically to the swim bladder disorder.

You will begin to see problems with the buoyancy of the fish. It can begin to sink to the bottom or float upside down. It also seems to have a swollen belly and fight with swimming and balance.

The most common causes are the swim bladder compression by other organs that enlarge. That is, a enlarged stomach too much air or Eat excessively. Less common causes include: tener an enlarged liver, enlarged intestine or enlarged kidneys. Bacteria or parasites, as well as mechanical problems and birth defects can also cause swim bladder disorder.


To prevent Swimming Bladder Disorder, keep your tank clean and make scheduled water changes. Defrost and soak food before feeding and definitely avoid overfeeding. This is one of the common diseases of aquarium fish.

The Flukes its about tiny parasites similar to worms that enter the skin, gills and other parts of the body of the fish. This is another common disease of fish.

You can notice that your fishscratch against objects in the tank. You can also see layers of mucus or silt on the gills or body, lesions, small spots of blood. Or gills with rapid movement, chewing fins or gills, red skin, discolored or pale fish or with fast breathing.

Your fish can show signs of lethargy, intermittent swimming, shallow breathing or minimal movement.

Bad water conditions, overcrowding, incompatible tank mates and stress.

Prevention is the key

Dealing with common fish diseases is no fun, and we are sure you don't want to see fish suffer or go through stress. Prevention is the key to make sure your tank mates have long and happy lives.

Remember buy fish that are free of all signs of stress and disease. When choosing a fish to buy, take your time to make sure the other fish in the tank are healthy.

It would be a good idea even place all new fish in a quarantine tank for 2 weeks. This to ensure that your newly bought fish will not bring new parasites and contaminate your tank.

If you buy new plants, make sure they are clean before placing them in your new tank. Keep movements and handling to a minimum when you buy new fish to reduce stress.

Avoid drastic changes in the water, keep the tank clean and the water parameters stable. Feed your fish a healthy diet and be careful not to populate your tank. All this will help you prevent common fish diseases.

Diseases caused by parasites

When fish are attacked by parasites they usually lose their appetite, they become more inactive and in some cases they rub against aquarium walls or decorative elements.
We will know that we are facing a parasite attack, because We will appreciate morphological changes: excess skin mucus, spots and in some cases, unsightly worms.
It agrees start a treatment as soon as possible with the correct medication, to avoid the worst possible outcome: the death of the fish.

Fungal diseases in cold water fish and tropical fish

Fungal diseases they go quite unnoticed at first, since we have no physical evidence of the disease at the beginning.
We know something happens to our fish because Their attitude has changed, they are behaving differently than usual.
Over time if physical alterations appear, the fungus reaches the surface of the skin and becomes visible as cotton flakes.
There are about 35 different species of aquatic fungi, although there are two genera that usually attack aquarium fish: Saprolegnia and Achlya.
It doesn't matter to know or recognize which one is attacking our fish, since the symptomatology is similar and the treatment too.
Fungi attack aquarium fish when there is a weakening of the mucosa that covers them, which may be due to various circumstances, such as poor water quality caused by an increase in nitrates, or the weakness of the specimen due to other diseases.
Sometimes fungal attacks occur after having suffered the white spot, or any type of bacterial attack.
The first symptom is a change in fish behavior. At that time we should carefully observe his entire body, to discover what happens.
In one or two days, the fungus begins to grow outward, we can see small white spots, which will then become like cotton flakes or long wool-like filaments, depending on the type of fungus.
Treatment of fungi in the aquarium
To treat fungi in the aquarium, when they are in their initial phase, Two treatments can be done: a topical one aimed at treating the affected fish locally, if we know where the fungus is located, and another for Perform medicinal baths.
In the first we will use potassium dichromate or potassium permanganate, applying directly on the affected area. We will use a solution of the product in water.
For the second treatment we will use methylene blue dissolved in water, we will make baths, which we will combine with baths in water with coarse salt.
Once the fungi are visible, we will use an aquarium-nursing, in which we will dissolve Trypaflavin to treat fish.
If the fungus has affected most of the fish, it is advisable to remove all the decorative elements and disinfect them. The aquarium is disinfected with fung>

  • Contains one (1) API bettafix antibacterial and antifungal fish Betta infection and fungus Remedy 1.7-ounce bottle
  • Heals bacterial infections, repair damaged fins, ulcers, and open wounds and promotes fin growth
  • Freshly incorporated sweet fish to reduce the risk of disease outbreak and heal wounds and tissue injuries
  • Contains healing Melaleuca, a variety of tea tree

Diseases in the aquarium caused by bacteria

The infectious diseases caused by bacteria They are usually detected because the fish become inactive, lose color, show frayed fins, their bodies swell, their eyes become cloudy, they appear with abscesses, redness or swelling of the fins and difficulty breathing.
An injured fish can be affected by bacteria, Therefore, it should be treated very carefully, as well as the rest of the aquarium fish, which may be affected by the product we use for healing.

Aquarium fish diseases caused by viruses

Virus diseases They are almost impossible to detect and treat. While for the rest of the fungal, bacterial or parasitic diseases there is a great documentation and treatments, for the viruses no.
To prevent the occurrence of any type of virus attack in the aquarium, whenever we buy new copies, they have to go through their quarantine period.
In the event that we are clear that one of our fish has been attacked by a virus, it is best to put it in a quarantine aquarium, monitor it and take it to an expert who can certify that it is so.
We probably have to get rid of the copy.