Freshwater Aquarium Fish Diseases, Symptoms & Remedies

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Just like any other pets, fish too can get sick. Before you start using any medication for them, you’ll need a proper diagnosis and you’ll need to pinpoint the cause of the disease.

Even though home aquariums may give you the impression that fish can be better guarded from diseases, fish do get various infectious, viral, fungal, bacterial, and parasitic diseases too.

In this comprehensive guide to freshwater aquarium fish diseases, I will list the symptoms of the most common fish diseases along with the remedies you can try.

And because prevention is always the best remedy, I’ll also offer some tips on how to keep your fish healthy, strong and happy.

Common Diseases Affecting Freshwater Aquarium Fish

For a better understanding and overview of the various fish diseases, I’m going to discuss them by grouping them into the following categories:

  • Parasitic Infections;
  • Fungal Infections;
  • Viral Infections;
  • Bacterial Diseases;
  • True Worm Parasite Diseases;
  • External Arthropod Parasite Diseases.

These are the most common fish disease categories that you should know about if you’re keeping or planning on keeping freshwater fish.

Parasitic Infections

In this category I’ll discuss the symptoms, possible causes and remedies for the White Spot Disease, the Gold Dust Disease, Hexamitiasis, and the Neon Tetra Disease.

1. White Spot Disease (Ich/Ick)


The Ich or Ick is caused by a protozoan that attaches itself to the body, gills, and fins of a fish and it appears as clearly visible white spots concentrated on these areas on the fish’s body.

Unfortunately, this type of parasitic infection is very persistent and can cause mobility and breathing problems to infected fish. If it’s left untreated, it can even lead to death.


  • White spots that look like grains of sugar or even white patches that appear on the gills, fins and body of the fish;
  • Fins folded against the body;
  • Difficulty breathing, fish coming to the surface of the tank for air;
  • Lack of appetite;
  • Fish trying to rub against objects in the aquarium in an attempt to remove the parasite;
  • Disoriented swimming.

Possible Causes:

  • Sudden changes in water temperature (e.g. in winter when temperatures drop, or when performing water changes if replacement water is not at the same temperature as the tank water);
  • Introduction of new fish that carry the protozoa in a poorly maintained tank;
  • Introduction of new plants that carry the protozoa.


As mentioned, this disease can be fatal for your fish and once it gets into the tank, it’s important to treat it immediately because the outlooks for your fish are grim – the disease carries a 100% mortality rate if left untreated.

Treatments for the white spot disease include:

  • Medication (anti-parasitic);
  • Increasing water temperature (86 F if tolerated by your fish);
  • Combining aquarium salt (not table salt!!!) into the aquarium.

You can pick up anti-parasitic medication at your local pet shop or order it online. The reason why you should also increase the water temperature is to speed up the lifecycle of the parasite.

Before administering any medication, make sure your remove your carbon filter because it may absorb medicine before it gets into the system of your fish, rendering the whole treatment useless.

Increased temperature alongside aquarium salt can disrupt the fluid regulation of Ich and helps in the production of slime or mucous to keep the parasite off the body of the fish.

2. Gold Dust Disease (Velvet)



Rust or Gold Dust Disease is another common parasitic infection that should be addressed as soon as you notice any signs. It also referred to as Velvet disease.

The disease is caused by the parasite Oodinium that attaches to the skin and gills of the fish creating a fine yellow or light brown film.

Unfortunately, visible physical signs appear only in later stages of the disease. Therefore, immediate action is required to prevent the death of your fish.


  • Light brown or yellowish film on the skin;
  • Skin peeling off (in advanced stages);
  • Fins folded against the body;
  • Weight loss, loss of appetite;
  • Lethargy;
  • Rapid breathing, difficulty breathing;
  • Scratching against surfaces.

Possible Causes:

  • Caused by the parasite Oödinium in poorly maintained tanks;
  • Sudden changes in water temperature;
  • Lack of regular water changes;
  • Adding new fish to the tank that are already infected with the parasite;
  • Adding plants that carry it.


Because it’s highly contagious, it’s important to act immediately to prevent the escalation of the disease. And because symptoms are difficult to spot early on, immediate treatment is crucial.

Gold Dust Disease remedies include:

  • Medication (copper sulfate, acriflavine, methylene blue, formalin, malachite green);
  • Dimming lights or cutting out light completely and leaving the tank in darkness (the parasite relies somewhat on photosynthesis for energy);
  • Raising water temperature if fish can tolerate it.

Increasing water temperature is not always a good idea as it can cause further stress or even weaken immune systems of certain fish. Therefore, apply it only if your fish can otherwise tolerate it.

3. Hexamitiasis

This disease is common to fresh and saltwater fish and it’s also known as Hole-in-the-Head Disease or Head and Lateral Line Erosion. It manifests itself as lesions on the head and flanks of the fish.


  • Subdued coloration;
  • Loss of appetite;
  • Lesions on head;
  • Fish may have trouble swimming;

Possible Causes:

It is believed that the parasite may be naturally present in low levels the intestine of some fish.

When the immune system of the fish become compromised either because of nutritional deficiencies or improper tank conditions, it leads to the rapid multiplication of the parasite.

The use of activated carbon in closed ecosystems may also be linked to the disease.


Removing activated carbon from the tank, improving water conditions with regular tank cleaning and water changes, and adjusting the diet of your fish have all been shown to improve the condition of infected fish.

Medicated fish food when fish are still able to eat or treatments with Metronidazole when fish are no longer able to eat are both used as a treatment option for this disease.

4. Neon Tetra Disease


This disease is named after Neon Tetra fish; however, it can affect a variety of Tetra species not only the Neon Tetra.

The disease manifests as a series of bacterial infections that invade the stomach and digestive tract of the fish, eating them from the inside out.

It’s caused by the parasite Pleistophora Hyphessobryconis, which feeds on the fish until the fish dies.


  • Loss of color or milky/brownish coloration;
  • Cysts on the body of the fish;
  • Weight loss;
  • Curvature of the spine in extreme cases;
  • Erratic swimming or swimming difficulties;
  • Separation from school;
  • Secondary infections.

Possible Causes:

The parasite Pleistophora Hyphessobryconis may end up in the tank via live food that may carry it. Other fish can get infected by eating the body of a dead fish that died as a result of the disease or carries it.


Unfortunately, the Neon Tetra Disease has no known medical treatment or remedy. The best thing you can do is to contain the disease by removing infected fish from the tank.

In this case, prevention is the best medicine – regular tank cleaning, frequent water changes and quarantining new fish and being picky about the food you feed them is the only way to prevent the disease.

Fungal Infections

Fungal infections are another category of diseases that can affect fish if proper tank conditions are not kept and fish have a compromised immune system.

I’ll discuss the symptoms, causes and treatment of two common fungal infections – the Body Fungus and the Cotton Fin Fungus.

1. Body Fungus

If you maintain a clean tank and healthy fish, fungus shouldn’t be a problem since the slimy coat on the fish protects against the spores of fungi.

However, if your aquarium is not suitable for healthy living conditions, you better believe it that the slimy coats of your fish become damaged and fungi will find their way onto the skin of your fish.


  • White fluffy patches on body, head or fins;
  • White patches can appear brownish, greenish, or reddish because of debris in water;
  • Behavior is not usually affected.

Possible Causes:

Anything that weakens the immune system of your fish – improper tank conditions, improper temperature, other diseases – can be a potential cause of this fungus.

Every time the mucous layer of your fish is affected even if it’s caused by rough handling, other fish nipping at it, diseases that cause open wounds and ulcers (e.g. Ich, Hole-in-Head Disease), will expose your fish to fungus.


If left untreated fungus will kill your fish, therefore, it’s important to act as soon as you notice the first signs to prevent it from spreading to your other fish.

You can pick up a number of antifungal medications from a pet store or order them online, most of which are based on organic dyes.

Sometimes, if some of your fish don’t tolerate antifungal medication, you’ll need to isolate infected fish and treat them separately in a hospital tank.

2. Cotton Fin Fungus

Cotton Wool Disease or Cotton Fin Fungus can appear if your fish have a weakened immune system.

Like many other diseases on this list, this too must be addressed immediately to prevent further damage.

It’s often mistaken for Cotton Mouth Disease, which is usually located on the mouth, scales and fins and has a more granular shape with grey-white coloration.

Even though it looks like fungus, Cotton Mouth Disease is actually caused by the bacterium Chondrococcus columnaris.


  • Wooly, cotton-like fluffy growths on the fins;
  • No immediate behavioral signs.

Possible Causes:

Improper tank maintenance may be one of the underlying causes of this fungal infection. Fish with a weakened immune system are more susceptible to getting the disease.

Even with regular and meticulous tank cleaning habits, your fish may get this disease if your fish have sustained injuries from other diseases or because of fighting with other fish.

Whenever you’re keeping fish of different species, make sure to check that they’re compatible and separate fish that bully or nip at the fins of other fish to avoid injuries.


Fungal treatments are the best cure for this disease with salt, Methylene blue, Malachite green, and Acriflavine being the most common ones. You may no longer find the last one since it’s toxic to humans.

You can use the other three including aquarium salt, which you can add to the tank in amounts of 1-3 grams per liter.

Viral Infections




Lymphocystis is the most common viral infection that your fish can get, and it’s introduced into the tank via infected fish or infected live food. It can infect freshwater and saltwater fish alike.

Thankfully, this infection rarely causes death, but it can make breathing and swimming difficult, plus it will usually disfigure fish.


  • Growths that resemble small cauliflowers on the skin or fins;
  • Breathing and swimming difficulties when the growths appear on gills or fins.

Possible Causes:

Because the virus that causes Lymphocystis is introduced to the tank, it’s important to quarantine new fish before adding them to an established tank.

Feeding your fish live food can also cause the infection, so growing live food at home or sourcing it from a reliable vendor is best.

If your fish don’t rely on live foods for sustenance, it’s best to avoid live foods.


To the disappointment of aquarists struggling to eradicate this viral infection from their aquariums, there is no ready-to-use treatment currently available for Lymphocystis.

For now, maintaining excellent water conditions, meeting the nutritional needs of your fish while hoping the disease resolves itself is the best course of action.

And it usually does resolve itself in a couple of weeks for warm water tanks and up to 6 weeks for cold water tanks.

Complications that may arise as a result of this infection include secondary infections when growths cover important areas such as the gills.

Parasitic, fungal or bacterial infections may appear; therefore, you’ll need to isolate the fish and treat it with appropriate drugs if you notice any signs of secondary infections.

Bacterial Diseases

In this section, I’ll cover the 8 most common bacterial fish diseases, so that you’ll know the identify the signs of disease, the root cause and the treatment options available.

1. Cotton Mouth Disease



This highly contagious bacterial disease is caused by the Chondrococcus columnaris bacterium and even though it’s a bacterial disease, it’s often mistaken for a fungal infection because of its mold-like appearance.


  • Fungus-like patches on the gill filaments (white-gray color);
  • Skin ulcerations;
  • Lightening or browning of gills;
  • Mucus on gills, head or dorsal regions;
  • Loss of appetite;
  • Rapid breathing;
  • Epidermal loss;
  • Ragged fins.

Possible Causes:

The disease can appear as a result of many factors including:

  • Overcrowding;
  • Poor tank conditions;
  • Inadequate diet;
  • Unstable water pH;
  • High bio-load in the tank;

Basically, any of these stressors can cause the disease to appear and the bacterium can stay active in the tank as many as 32 days if tank conditions permit.


Outlooks for the disease aren’t good – often the disease is fatal to fish that contracted it. It’s also highly contagious, so quick action to help contain the disease is necessary.

Possible treatments include salt solution (1% or higher) baths for infected fish. If the disease is at the tank level, medication should be used in the entire tank.

Antibiotics that target am-negative bacterial infections like Oxytetracycline are effective.

If you see dead fish in the tank, remove them immediately to avoid spreading the disease even further.

2. Hemorrhagic Septicemia



The Red Pest – as it’s often described as – is caused by bacteria entering the circulatory system of fish, causing damage throughout the body including blood vessels, tissue and the heart.

Hemorrhagic Septicemia is a serious condition that causes internal bleeding and read streaks to appear on the body of your fish, hence the name Red Pest.

Hemorrhagic Septicemia can also lead to Dropsy as a result of fluid build-up in the body.


  • Bright red streaks on fins, red discoloration on flanks;
  • Bloated abdomen;
  • Bulging eyes;
  • Open sores;
  • Fast breathing;
  • Erratic swimming;
  • Coming to the surface of the tank for air.

Possible Causes:

The underlying cause of Hemorrhagic Septicemia in fish is poor tank conditions, which cause bacteria to overgrow and ammonia levels to spike.

Improper water conditions with poor Redox and high nitrate levels are also to blame when fish contract the Red Pest.


Since there is no known cure to this disease, experimenting with several options may be required to see which produce results.

Bear in mind that since the disease is in the circulatory system of the fish, external medications and measures may no longer be efficient.

If you notice the symptoms of the Red Pest in your fish, you can try the following possible remedies:

  • Treating the aquarium with disinfectant and cleaning the tank (try 0.2% Acriflavine or Monacrin solution at a rate of 1 ml/l);
  • Adding chloromycetin or tetracycline antibiotics to fish food (mix one 250 mg capsule to 25 g food).

Since once of the symptoms of the disease is loss of appetite, keeping your fish hungry before adding the antibiotic to their food may be a good idea to make them eat the mixture much faster.

The recommended disinfectants may color your tank, so don’t worry if the water turns into a different color after adding the disinfectant.

With time, the disinfectant dissipates, and the color of the water returns to normal.

3. Tuberculosis


Fish TB is caused by one of the 11 species of Mycobacteria and it’s common in poorly maintained tropical aquariums.

Symptoms of the disease may be slow to show themselves and they appear only after infection occurs. It’s not highly contagious and it takes some time to develop, but there’s no cure.


  • Lethargy;
  • Loss of appetite;
  • Loss of fins and scales;
  • Hollowed belly;
  • Paleness;
  • Reclusiveness;
  • Yellowish or darkish nodules on body;
  • Skin ulcers.

Possible Causes:

Fish tuberculosis can be caused by lack of tank maintenance and overstocking the tank. Mycobacteria can thrive in aquariums where water conditions are precarious.

Any of the 11 species of this bacterium (M. fortuitum, M. flavescens, M. chelonae, M. gordonae, M. terrae, M. triviale, M. diernhoferi, M. celatum, M. kansasii, M. intracellulare, and M. marinum) can develop and cause fish TB.

Low oxygen in the tank, low pH, high levels of soluble zinc, fulvic and humic acids are all breeding grounds for these bacteria.


As with many other diseases that I discuss in this article, fish TB has no known cure or remedy.

If the infection is at an aquarium level, the best course of action is euthanasia of the fish and starting all over with the aquarium (after proper disinfection of course).

I don’t recommend that you continue keeping fish that are sick since things will only get worse and your fish will have no quality of life – they’ll struggle with chronic health problems, developmental issues, and they’ll be a constant source of infection.

Also, take care not to put your hand in the tank if you have any cuts or scratches and never use anything from the tank in the house. It’s unlikely, but possible for humans to contact the disease.

It’s best to be safe and treat it as a possible source of disease for you and your family.

4. Bacterial Fin Rot



Bacterial Fin Rot is a disease that attacks the tissue starting with the fins and may slowly spread to other areas of the body once it reaches the base of the fins.

Unfortunately, lost tissue can no longer regenerate, therefore, Bacterial Fin Rot causes permanent damage to your fish.


  • Regions attacked by Bacterial Fin Rot appear milky-white;
  • Fins look shredded;
  • Fin rays can be exposed;
  • As the disease progresses it causes difficulty swimming.

Possible Causes:

Although Fin Rot is caused by various bacteria such as Pseudomonas, Flavobacterium Columnare, and Aeromonas, the root cause is always poor water conditions in the tank.

Fish are also more vulnerable to the disease if they’re stressed, if the tank is overstocked, if they’re housed with aggressive fish that may injure them or nip at their fins.


Assessing the environmental factors of the fish is the first step towards dealing with the disease.

If your tank is overcrowded, rehome some of the fish. If you notice fish nipping at other fish or being aggressive, remove them from the tank.

Next, do a thorough tank cleaning and several 20-50% water changes with clean, aged water.

After cleaning the tank and removing debris and detritus, check for water parameters including levels of ammonia, nitrites, and nitrates.

The last line of remedy is treatment with antibiotics and for this you’ll need to separate affected fish and treat them accordingly. Choose antibiotics that target gram-negative organisms.

5. Popeye





Popeye is a disease that affects the eyes of your fish to the point where eyes could fall out of their sockets.

The disease is the result of a hemorrhage produced by gas in the capillaries of the eye socket. Because of this, eyes may protrude and even fall out if left untreated.

Because Popeye is a mix of problems – infection, cornea damage and fluid build-up behind the eye, treatment can be difficult.

The disease is rarely fatal to the fish, but it’s important to prevent the spread of the disease.


  • One or both eyes protruding from the eye socket;
  • Cloudy or bloodstained eyes;
  • Ruptured eye;
  • Loss of vision;

Possible Causes:

When both eyes are protruding, the disease is called Bilateral Popeye and its most likely cause is infection caused by prolonged exposure to precarious water conditions.

It can appear even in tanks where the nitrogen cycle hasn’t fully completed, but mostly in tanks where maintenance is non-existent or lax.

If only one eye is protruding – in which case we’re dealing with Unilateral Popeye – the cause is most likely fights between fish, scraping of the eye, rough handling or collisions between fish.


First, make sure water conditions aren’t the cause and make necessary adjustments. A healthy aquarium and a healthy diet (rich in vitamins) can help heal minor corneal damage and reduce swelling.

In more advanced cases, you may need to set up a hospital tank and treat affected fish separately.

Possible remedies include:

  • Epsom salts added to the tank in a dose of 1-3 teaspoons/gallon;
  • Medications that work for Fin Rot may be useful in preventing a damaged cornea developing into a full-blown Popeye disease;
  • Once the disease develops, antibiotics used in treating internal and systemic infections mixed into food is the best course of action.

6. Dropsy


Dropsy is an infection that causes fluid to build up inside the fish, which damages its internal organs. The infection is caused by a bacterium that lives naturally in aquariums.

Fish become sensitive to this bacterium if their immune systems are weakened or compromised. Once the disease settles in, mortality rates are high even with treatment.


  • Bloating;
  • Extruding eyes;
  • Scales sticking out;
  • Lethargy;
  • Loss of appetite;
  • Rapid gill breathing.

Possible Causes:

Caused by the bacteria Aeromonas that’s naturally available in all tanks, Dropsy affects fish with a weakened immune system due to stress.

Overstocking the tank and poor water conditions can weaken the immune system of fish and cause Dropsy.

The kidney function of fish becomes compromised, which leads to absorption of water into the body cavity, which causes the bloated appearance of fish with Dropsy.


Unless you identify the disease in its early stages, you won’t be able to save your fish from dying.

Isolating the fish in a separate tank and adding Epsom salt (⅛ teaspoons to 5 gallons of water) can help draw out some excess water from tissues and body cavity.

If your fish will take food, adding antibacterial medication to their food (e.g. Maracyn Two) can also help.

7. Cloudy Eye



Cloudy eye is also a common fish disease that can be caused by poor water quality, malnutrition, stress or old age.


  • Cloudy/hazy eyes;
  • Loss of vision;

Possible Causes:

Water quality is probably the number one cause of this issue, however, an increase in parasites malnutrition, old age or stressful tank conditions can all contribute to the disease.


If you notice the symptoms of Cloudy Eyes, you should start with examining water parameters including pH values. When pH drops too low, it can cause these issues in your fish.

Perform water changes if pH values are below 6.4. Once levels are adjusted, your fish will recover.

If water changes and pH level adjustments don’t seem to do the trick, try administering Melafix, which is a natural treatment for bacterial fish infections.

8. Swim Bladder Disease



Swim Bladder Disease is a catch-all name for diseases that affect the swim bladder of your fish. Although it’s more common to Betta and Goldfish, it can affect other species as well.

It can be caused by birth defects, bacterial or parasitic infections, physical damage, any of which affect the proper functioning of the swim bladder.


  • Swollen belly;
  • Curved spine;
  • Swimming abnormalities (e.g. fish sinks to the bottom unable to rise up, fish floats to the top upside down, tail is higher than head when swimming, etc.).

Possible Causes:

Inflammation to the bladder caused by bacteria and parasites is one of the causes of the Swim Bladder disease.

Other causes include:

  • Physical damage as a result of a fall or fighting;
  • Deformation as a result of breeding;
  • Compression because of overeating, gulping air, or rapid eating;
  • Compression due to enlarged stomach when eating foods that may expand.

Blood Parrot Cichlids and fancy Goldfish are examples of fish that may have bladder issues because of breeding and injuries or even constipation can affect them more than other species of fish.


If the underlying cause is a parasitic or bacterial infection, medication like broad spectrum antibiotics can help.

But if the issue is a birth defect, there isn’t a treatment or medication that can help, and you’ll need to make some adjustments in the tank like raising temperature by a few degrees.

If the fish are not having normal bowel movements, skipping feeding for 3 days and offering skinned and cooked peas on the 4th day can resolve the issue.

Some aquarists also recommend lowering the waterline while taking care to leave a few inches above the height of the fish to avoid exposure to dry air.

True Worm Parasite Diseases

Flukes and Roundworms are the two most common True Worm Parasite diseases in fish. Unlike other parasitic diseases, these ones can infect even healthy fish.

Let’s see which are the symptoms, causes and treatment options for each of these diseases.

1. Flukes (Skin and Gills)

Flukes is a catch-all term for various parasites that can affect the gills and skin of fish, which explains why the disease if also referred to as Skin and Gills Flukes.

Although environmental factors such as stress and poor water conditions are often linked to Flukes outbreaks, even healthy fish can be exposed to this disease.


  • Gills and body covered by a layer of mucus;
  • Red skin;
  • Gills have the appearance of being chewed or shredded;
  • Scratching against objects;
  • Breathing difficulties;
  • Paleness, drooping fins, hollow bellies and rapid breathing are signs of an extensive infestation.

Possible Causes:

Dactylogyrus spp. and Gyrodactylus spp. are the most common parasites to infect freshwater and marine fish.

Parasites attach to the skin of fish and burrow themselves into their flesh, leaving ulcers that can be exposed to secondary infections.

Parasites can also attach themselves to the gills of fish, causing breathing difficulties and reducing the ability of fish to take in oxygen. As a result of infection and lack of oxygen, your fish can die.

Stressors like bad water conditions, an overstocked tank, high ammonia levels can all contribute to outbreaks of the disease.

These parasites are naturally present in aquariums and stressful conditions like the ones I mentioned can cause overgrowth and health problems.


Using anti-worm medications like Praziquantel have been proven to effectively treat Flukes and infections caused by Flukes.

Beyond treating Flukes and associated infections, this medication is in no way harmful to other species, plants or filters in the tank, so you can use it without worries.

2. Roundworms (Nematodes)

No fish is safe from Roundworms, which can attack all organs and result in fatalities. Because they’re so difficult to treat, the first line of defense against them is to avoid introducing them into your aquarium.


  • Worms visibly hanging out of the anus;
  • General lethargy;
  • Loss of appetite;
  • Belly sink-in (severe cases).

Possible Causes:

Roundworms are introduced into the tank via raw foods, driftwood, or new fish that already carry the worm.

Leftover food left to decay in the tank can increase the chances of an outbreak, so keep your tank tidy and clean, and remove any decaying food.

If a few Roundworms may find their way into your aquarium, and the water conditions are great, and your fish are strong and healthy, they may not cause problems.

However, once water quality decreases and the immune system of your fish becomes weakened, Nematodes can and will cause issues.


Keeping the tank clean by scooping up leftover food and perhaps introducing some natural tank cleaners (Plecos, Gouramis, etc.) can go a long way in preventing outbreaks.

When the problem is already present in the tank, medication is the only way to get rid of the worms. Try Parachlorometaxylenol either as a bath solution (10 ml to one liter) or mix it into their food.

Another option is Thiabendazole mixed into fish food, however, you may have a hard time finding this medication or getting your fish to eat the medicated food.

External Arthropod Parasite Diseases

In this section, I’ll focus on two external arthropod parasite diseases, one of which is extremely rare, the Anchor Worm, and the other is one of the largest parasites to infect fish, known as Fish Lice.

1. Anchor Worm

Despite the name “worm”, these parasites are a species of small crustaceans specific to freshwater fish. They’re not at all common, and when they do appear, they’re easy to spot.

As their name suggests, they anchor themselves deep into the fins or dorsal area of your fish, opening the way to secondary infections and other diseases.


  • Inflammation, ulcers on body;
  • Redness at anchor point;
  • White-green or red “worms” located at the base of fins;
  • Lethargy;
  • Rubbing against hard objects;
  • Breathing difficulty.

Possible Causes:

Anchor worms are introduced into the tank either by adding plants that carry them or by adding new fish infected with anchor worms.

Therefore, disinfection of plants and quarantining of new fish is recommended before you add them into an established aquarium.


There are various treatment options available to deal with anchor worms:

  • Potassium permanganate (as tank treatment or dip);
  • Salt dip;
  • Formalin dip;
  • Removal with tweezers.

Removing anchor worms with tweezers is the surest way to ensure they’re gone, however, only if it isn’t borrowed too deep into the fins.

Risks of using this method include breaking the tail off, leaving the head of the worm in, trauma to the fish.

2. Fish Lice

Fish Lice or Argulus can grow up to 10 mm in size, which makes them easy to recognize. They’re usually located in sheltered areas like behind fins or around the head.

Once Argulus attaches itself to the fish, it feeds off of them causing irritation and inflammation.


  • Small dark spots on fish;
  • Ulcers, irritated and inflamed areas, red markings;
  • Rubbing against hard surfaces;

Possible Causes:

Fish lice are introduced into the tank often while transferring pond fish into an aquarium. Lice spreads fast spreading diseases and infections. Immediate treatment is required.


Using specialized medication on a tank level is the best at addressing this issue. Organophosphates deliver the best results against Argulus.

Manual removal is another option, however, treating the entire tank is still required. If you’re going to remove lice manually using tweezers, make sure you use antiseptics to clean the wounds left by the lice.

As with other diseases that are introduced into the tank through food or other fish, quarantining is one of the best prevention methods.

Talking about prevention, make sure your read the tips below on how to prevent disease outbreaks or minimize the risk of diseases in your fish.

Fish Disease Prevention Tips

Dealing with fish diseases of any kind is a source of stress for many aquarists and while many of the diseases I touched upon in this article are treatable, unfortunately, many are not.

Therefore, in those cases, minimizing exposure to diseases is the best defense in making sure your fish stay strong and healthy.

Here are some easy tips to stay on top of the most common diseases affecting freshwater aquarium fish:

1. Feeding them a Balanced Diet

A nutrient-rich balanced diet is crucial to making sure your fish build up a strong immune system that’s ready to fight off infections and other diseases.

Nutritional deficiencies can often be the reason why fish are not equipped to properly fight off infections or heal when injured.

Make sure you research the nutritional requirements of your fish, making sure they get all the nutrients they require to develop and stay healthy.

Not feeding your fish enough can cause problems, but the opposite is also true — overfeeding your fish can also be a potential source of diseases due to the accumulation of toxins in the tank.

2. Avoiding Sudden Changes in Tank Conditions

Many fish are sensitive to dramatic changes in tank conditions, which can happen is you’re an inexperienced aquarist.

Sudden changes in temperature and toxin levels are often the main culprits in exposing your fish to undue stress, leading to a weakened immune system and disease outbreaks.

This is the main reason why beginner aquarists are recommended to set up their first tank with hardy fish species that can better withstand a variety of tank conditions.

Proper equipment like a pre-set heater and a quality filter system can go a long way in maintaining stable conditions in the tank.

3. Maintaining Quality Water Parameters

As I mentioned, having quality equipment like a good filter system can go a long way in maintaining quality water parameters. However, equipment alone is not enough.

Regular water changes — weekly or bi-weekly, depending on your fish’s bio-load — is also crucial in diluting and removing toxins and replenishing water with essential nutrients.

Other than changing water, regularly cleaning the tank by removing leftover food and debris can also prevent diseases and keep algae growth at normal levels.

Make sure to also test the water for ammonia, nitrites and nitrates to keep an eye on toxin levels and potential fluctuations.

Another important aspect to remember when it comes to quality water parameters and tank conditions is to avoid overstocking the tank, which can cause stress and spikes in toxin levels.

4. Monitoring the Health of Your Fish

Another way of preventing diseases from becoming too serious is to spot them in their early stages.

To be able to do this, you need to familiarize yourself with the various diseases that can affect your fish.

Reading articles like these, becoming familiar with symptoms and treatment options can go a long way in detecting diseases early on, at least the ones that produce early symptoms.

Therefore, whenever you’re feeding your fish or cleaning the tank, take a few minutes to look at your fish and assess their general health level.

5. Quarantining New Fish

You’ve set up an aquarium, added some fish, but there’s plenty of room for more fish. So, you’re thinking of adding new tank mates to your existing fish.

Before you add any new fish to the tank, it’s best to set up a quarantine tank with the same water conditions as in the target tank and monitor your new fish for a couple of weeks, just to make sure there aren’t any problems with them.

If everything seems to be in order, you can add the new fish to the established tank, all the while continuing to monitor your fish for any signs of diseases.

6. Being Circumspect with Everything You Add to the Tank

Because a lot of diseases are carried into the tank via raw food, plants, other fish, and decorations, you need to be very careful with where you source these things from.

Disinfect plants and decorations before adding them to the tank, because they can carry cysts and protozoa on them.

Be careful with raw foods and new fish as they can carry parasites, worms, and infections. Be picky about new fish, foods and other things that can carry diseases.


All pets can get sick and so can your fish. The key is to recognize when something is off with your fish and identify the underlying issue, which can be anything from stress to poor water conditions.

Sometimes, even with the biggest care and attention, diseases can still strike. In such cases, getting the right treatment on time is crucial in saving the lives of your fish.

And more importantly: Whenever possible, make sure you consult a professional if you have concerns about the health of your fish. Articles and guides like this are just that — guides that don’t replace professional medical advice.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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