Diseases and treatments for fish



White spot disease In freshwater aquariums it is caused by the presence of small ciliated protozos called Ichthyophthirius Multifiliis. The action of this pathogen can be aggravated by the appearance of other parasites that affect the skin and the animal's brochures.

This disease is easy to detect due to white entrapments, which presents the affected fish in skin, fins and gills. These cysts can reach a millimeter in diameter and can form irregular scabs.

The type behavior of the animal is that of scratching against the decoration of the aquarium, while presenting the highly accelerated breathing rate.

The occurrence of bacterial infections is frequent.


The responsible Protozo of the disease uses in his life the body of his host to develop. Once mature, it falls off falling to the bottom of the aquarium, where after wrapping in a membrane it reproduces, forming hundreds of new individuals that go out in the open air in search of a new tenant to parasitize. If they don't find it in a short period of time they die.

A high volume of inhabitants in the aquarium implies more ease for this reproductive cycle to complete.


While the parasite is in the body of its tenant it is invulnerable to any chemical treatment, it is because it is embedded beyond the outer layer of the skin of the fish. Therefore the application of any chemical treatment It is effective in the remaining phases of the reproductive process.

Currently there are various treatments that result in the market. 100% effective, managing to reduce the incidence of this disease to its lowest point. Therefore, if it is not complicated by the appearance of bacterial infections, the mortality due to this cause is 0%.

It will be necessary to pay attention when applying these chemical treatments for various reasons:

  • Fish that do not support it: Locha Clown or catfish No scales are sensitive to treatment based on chemicals.
  • Chronic Ich: Failure to correctly apply the medication sockets can eventually cause Ich resistant to treatments, being then difficult to eliminate even if its presence does not deteriorate the health of our fish in excess (There are many fish that once overcome the disease have a certain immunity)

There are some other methods to eliminate these parasites that require the following accreditations:

  • Increase the temperature, for several hours a day and for at least 3 days, at 32º C. It is always clear that the fish tolerate it.
  • Leaving the aquarium without fish for a minimum period of 7 days at a temperature below 20º.

There is a product marketed in pharmacies as a generic drug with the name of Metronidazole which is extremely economical and effective against this parasite (In case of not performing the full treatment we risk the Ich becoming resistant).

The application is supplied in tablets. One for every 25 liters of water. one application every 48 hours (it is convenient to carry it out at night with the light off, because the water turns white and can eventually drain the fish) together with an increase in the temperature of the tank (28-30º C ). After this period and when the medication is not removed, we must change the water and filter for three days with activated carbon.

Normally and after 6 days of treatment the Ich has disappeared from the aquarium. If it is persistent there is no contraindication to return to the treatment.

Prevention of diseases in tropical 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.

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:


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.

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.

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.

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


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.

Ways to recognize white spot disease in the aquarium

This disease is clearly observable by the presence of multiple white dots in the skin of our fish. These points, as we have mentioned, are the capsules where the invading protozoa develop. Its size can reach the millimeter in diameter so they are easily detectable.

At the beginning of the invasion the whitish spots are dispersed among themselves being more present in the fins. With the advance of the invasion the number of points multiplies until we can observe a massive invasion in the body of our fish. It is common that several points can be joined forming a major point known as a pustule.

In the particular case of the marine aquarium the white spot is primed with the gill area which allows to detect breathing problems in the fish, erratic movements and accelerated gasps.

Fish species affected by protozoan infection with higher virulence

Both the freshwater species Ichthyophthirius multifiliis as its marine replica does not have species more prone to infection but can be carried out on a very varied and numerous group of them. These protozoa can be found in the skin of fish from almost all parts of the world.

In wild habitats the white spot condition is almost nil while in aquariums and fish farms its action is much higher. These invasions also affect fish destined for human consumption, generating true epidemics among trout and catfish for example.

White spot disease in the freshwater and saltwater aquarium

Although they are not selective with the species to invade there are some more likely to suffer them. Among the freshwater species the Botias and in particular the Botia clown or Botia macracantha as well as most tetras are especially sensitive. These commented species also suffer a greater number of casualties than others such as cichlids that are also affected but have greater resistance to the action of the disease.

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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Effective treatment against invasive protozoa in fish skin

White spot infestations are so common in aquarium hobby that all commercial houses have their own treatment against them.. Under the advice of the store you go to, you can buy efficacy treatments with the disease whenever it is used following the instructions of its leaflet. It is very important to read this leaflet and not acquire treatments that lack it. We must know exactly how it acts in the aquarium and if other species can be affected, as is the case with invertebrates of both fresh and salt water.

During the cyst phase both in the capsule in the epidermis and in the substrate we can practically do nothing. It will be during the free swimming stage when they are vulnerable and are easier to eradicate.

For freshwater treatments, the marketed compounds are usually based on organic dyes like malachite green, methylene blue and acriflavin. They are also used inorganic compoundss such as sea salt, potassium permanganate or copper derivatives. The organic compounds employees are usually based on formalin.

For marine water, treatments are usually composed of copper derivatives, mainly copper sulfate.

White spot disease in the freshwater and saltwater aquarium

In those cases where the species tolerate it, the temperature of the aquarium can be raised by setting it between 30 and 32ºC over a few hours for several days running very well as a germicide.

Methods to prevent white spot appearance

The main reason for the occurrence of a white spot infection is usually an extreme case of stress such as the introduction of new fish, sudden drops in temperature or drastic changes in the physical-chemical parameters of water.

The parasite takes advantage of the lowering of the fish's defenses against a serious stress situation to infect their skin and begin the reproductive process. It is especially common when introducing new fish, so quarantines are a highly recommended practice to rid the rest of the partners of the exponential explosion of the presence of parasites.

In addition to the arrival of new tenants to the aquarium Sudden drops in temperature are another major cause of the onset of infection. It is essential to periodically check the temperature of our aquarium through the thermometer by regulating if necessary the heater thermostat. Forgetting to connect the heater after water changes is one of the most common causes of white spot appearance.

Chemical white spot considerations

Adding chemical treatments to the aquarium can damage natural plants and kill our invertebrates. That is why the dose and the counter indications for certain species should be checked well.

Medication in a nursing aquarium instead of the main As soon as the first parasitic capsules are detected on the skin, it would be the most appropriate but it is complex for most fans. In addition to the complexity of having two aquariums working it is also very complicated with certain decorations to catch the fish to move them from installation.

In marine aquariums you should never medicate with copper derivatives as they are lethal to all types of invertebrates. There are non-copper based treatments that are suitable for use in aquariums of this type. In addition to locating and using it effectively, the reasons for stress should be reduced and continue to be fed properly so that affected animals have a better chance of survival.

White spot disease in the freshwater and saltwater aquarium

If we have had the bad fortune of losing our fish due to these infections, we must leave the aquarium unpopulated until the protozoan strains die Not finding fish to colonize. If our fish survive, it is advisable to finish the treatment within the periods indicated in the leaflet.

He Ichthyophthirius multifiliis It takes 3 to 4 days to complete your full reproductive cycle at temperatures of 20 ° C. If the water temperature is lower this period is extended. In seawater theC. irritanshowever, it can only be developed with temperatures above 20ºC.

The presence of parasites in the skin also usually causes secondary pathologies such as bacterial infections since the animals scratch themselves against the decorative objects of the aquarium. In these cases, antibacterial treatments such as Terramycin (Oxytetracycline) can be used in doses between 10 and 20 mg per liter of water.

An effective treatment in marine facilities if we can catch the infected fish is to perform freshwater baths with an identical ph to that of the aquarium. Depending on the size of the fish, this bath can be prolonged between 2 and 10 minutes. Always under the strictest observation. On the contrary, freshwater fish with baths with a percentage of 30% seawater can always be treated always depending on the response of the fish. A traumatic personal experience It was to treat a group of cold-water telescope fish in this way. These fish that were black at the beginning of the bath changed their skin color to white and died later. It is an experience that I deeply regret.

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What is the white point or Ich?

White spot disease in fish is caused by a ciliated protozoan called Ichthyophthirius multifiliis. The most obvious symptom of this disease is the presence of small white dots, such as grains of salt, on the skin of the fish. This may be accompanied by movements to rub against objects by itching, irregular breathing and lowering of fish activity.

This parasite has, in broad strokes, two vital stages. One under the skin of our fish, where it feeds. And another free life, where it reproduces. The time to develop a cycle depends a lot on the temperature, being faster at higher temperatures

The parasite reaches our aquariums by other fish or by contaminated water. This parasite can attack immediately or remain dormant and in balance with our fish, until something weakens the fish (stress, poor diet, etc.) and then the parasite gives the face.

Medicine against white point has its problems

When our fish are sick the first thing we think is to go for a medicine. In the market there are many treatments against "the white point" (methylene blue, malachite green, metronizadol, etc). But there is something that we are rarely told, these treatments are quite harmful to our aquariums. On the one hand, they damage the bacterial flora of our filters. This makes it break the natural balance we have achieved in the aquarium, and therefore weakens our fish even more. On the other, these medications are toxic to many fish, including very common fish in community aquariums such as neons, plecos or corydoras.

We must be very careful with the medicines in the aquarium, as they can damage the flora of the filter. If he kills her completely, we would have the same problems as in an uncycled aquarium

What is the temperature treatment for the white point based on?

It consists of raising the temperature of our aquarium to 30-31 degrees (some fish may not hold it, so you have to make sure before, but the vast majority of conventional tropical species do withstand it). With this temperature it is possible that the parasite develops very fast and takes off soon from our fish (few days). In turn, that temperature is deadly for the free phase of the parasite, and therefore cannot be reproduced.

Methodology for curing the white point by raising the temperature

  1. Raise the temperature making a good acclimatization (see precaution 1).
  2. Increase the oxygen exchange of water. To do this, orient the filter so that it moves the surface a lot or add an aerator pump. You have more information about the problems and having the aquarium at a high temperature in this post, although we are now interested in having a high temperature, we must take precautions
  3. Maintain the temperature between 30-31ºC until the points have completely disappeared.
  4. Once there are no symptoms in the fish, keep the temperature elevated for at least one more week, to eliminate parasites that are in free phase.
  5. Slowly lower the temperature 1 degrees per day (now there are no emergencies and our fish will thank us).

Water changes must be made regularly or even increase their frequency. Since this way, in addition to eliminating the typical pollutants that the aquarium accumulates, we help reduce the burden of free parasites.

The feeding of our fish should remain optimal and take special care, since they are weak and they still have a harder time eating. If we see that this happens they can be fed with more quantity so that the healthy ones let the sick eat (watch out for the food not consumed), they can be chopped up and / or they can be helped with live or frozen food.

Turn off the light to the aquarium to cure white spot: false belief

Many people comment that with this technique you have to turn off the aquarium light. This is a misguided error of drug treatments. Malachite green, used as a treatment, is inactivated in the presence of light. Therefore, in the medicine they recommend having the aquarium in the dark. If we are not using medicines, it does not make sense to have the light turned off, since we do not obtain any benefits and the fish and plants, even if they survive a period of darkness, will not be in optimal conditions. We have already commented before that the white point can give them stress and that the fish must be in the best possible conditions to fight against the parasite.

However, if you have another scientific explanation that discusses this theory, let us know and we will correct this post.

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.