Freshwater Fish Diseases


Ammonia Poisoning

Possible Symptoms: Red or inflamed gills, rapid breathing, gasping at the surface of the water.

Possible Causes: Poor Water Quality; Overfeeding; Overstocked; Uncycled tank

ammonia reducerTreatments: Do a 20-30% water change daily to get the ammonia levels down. Changing too much of the water at once could possibly put your freshwater fish in shock and possibly cause more problems than what you have now. Ammonia literally burns your fish gills making it hard for them to breath properly and in some cases it will cause death. Always monitor your ammonia readings. If the water changes are not helping you can use an ammonia reducer you add to your tank to help bring it down.  However, it is only a temporary fix and the cause should be identified. Also, check your filter cartridges to ensure that you don’t have excess waste building up on it causing your ammonia spikes. Wash the filter out in fish tank water that you just pulled out for a water change and/or replace the aquarium filter with a new one ensuring it is being rinsed out completely before adding it to the fish tank.

Anchor Worms

anchor wormPossible Symptoms: Scratching or rubbing on objects in the tank; white-ish or green threads hanging on the body of the fish; inflammation where the anchor worms have attached to the fish

Possible Causes: Contamination from infected fish


Step 1: Do a water change making sure you vacuum the substrate well.

Step 2: Using tweezers, remove all visible anchor worms from all of the fish in your fish tank.

Step 3: Using clean aquarium water in a separate container large enough for all of the fish from your fish tank, mix a solution of Potassium Permanganate at a rate of 25 mg powder per liter of water. Once the powder is completely dissolved add the fish with no visible anchor worms in bath solution. Fish should be left in for 30 minutes.

Step 4: In your main fish tank, add Dimilin. This product is good for killing the adult anchor worms that were not removed from the vacuum and the larvae that was missed also. However, this product will not kill the anchor worm eggs that may still be present in the fish tank so it would be wise to treat again in 3-5 days to prevent another infestation.

Step 5:  Monitor your water quality and levels at least once a day. Your fish now have open wounds and poor water quality could lead to secondary infections that would require more chemicals in the fish tank.

Black Spot

black spot diseasePossible Symptoms: Irritated fish; rubbing on objects in the tank; small black spots or smudges on body and around mouth; blood loss if heavily infected

Possible Causes: This will affect pond fish. It is caused from a bird eating an affected fish. The black spots are actually encapsulated worms. After the bird eats the affected fish, the worms hatch inside of the birds digestive track and lays eggs. The bird passes the eggs in its fecal matter. The fecal matter that makes it to the water will hatch at which point it starts looking for another host.

Treatment: Epsom Salt bath.

Body Flukes

body flukesPossible Symptoms: Scratching or rubbing against objects in the tank; layer of mucus covering gills and/or body; rapid moving gills; gills and/or fins appear to be chewed on or eaten away; reddened skin; gills may appear to have ich; unusual racing around the tank; pale fish with drooping fins, rapid breathing and/or hollow bellies indicate a more extensive infestation

Possible Causes:  Poor water quality; overcrowding; stress from being bullied, incompatible tank mates

Treatments: If the infestation is from poor water quality, do more frequent water changes. If it is from overcrowding or incompatible tank mates you need to get another tank and remove the extra fish or incompatible fish. You can also treat your tank with Tetra Parasite Guard or any other Parasite medication.

Camallanus Worms

Camallanus WormsPossible Symptoms: Red or pink worms protruding from the anus of the fish; listlessness; bloating; refusal to eat; the worms can cause wasting away disease where your fish look as though they are wasting away from malnutrition; white feces

Possible Causes: Infestation from new fish

prazipro freshwaterTreatment: Your entire tank must be treated as the first stage larvae may survive for 3 weeks in the tank even without a host. Make sure to disinfect everything that comes in contact with the infected fish tank (water change buckets, siphons, nets etc.) Any towels that come in contact with the water from the infected fish tank should be washed separately from other clothing in hot water and bleach. Camallanus worms have developed immunities to common wormers on the market such as Prazi medications. Levamisde HC1 may be the most effective remedy for the infestation.

Clamped Fin

Clamped FinPossible Symptoms: Fins folded against body; listless behavior

Possible Causes: Clamped Fin could possibly be a symptom of another illness or disease; bad water quality; parasites

Treatment: Do a partial water change and if your fish can handle aquarium salt add it to the tank. If the clamped fin is from an infection you can use a multipurpose antibiotic such as Tetra Lifeguard or any other multipurpose remedy.

Columnaris (Mouth Fungus)

Columnaris (Mouth Fungus)Possible Symptoms: Cottony patches around mouth; white spots on mouth, around the mouth and/or chin; clear stringy feces; loss of appetite; rapid gill movement; may also affect fins and gills

Possible Causes: Highly contagious bacterial infection; stress; injury; poor diet; poor water quality; unstable pH

Treatment: Chloromycetin; Kanacyn; Maracyn and Maracyn 2 together; Copper Sulfate; Furan; Tetracycline; Malachite Green; Medicated foods does with Terramycin. In conjunction with one of these medications, perform a water change before adding in medication to help start the healing process with clean water.


Constipation fish diseasePossible Symptoms: Loss of appetite; swelling of the body

Possible Causes: Poor diet

Treatment: Change diet to a higher quality food. Dry food soaked in medicinal paraffin oil may also help. Switch between flake food and frozen food regularly and even adding fresh vegetables every few days as a snack (if your fish will eat vegetables) may help also.

Dropsy or Malawi Bloat

dropsy in fishPossible Symptoms: Bloating; protruding scales like a pinecone; loss or lessening of body coloration

Possible Causes: Bacterial infection of the kidneys; possibly from poor water quality

Treatment: Do more frequent water changes; use better quality food; May feed an antibiotic food of Chloromycetin or Tetracycline.

Fin Rot

fin tail rotPossible Symptoms: Fins appear to be rotting away; loss of appetite’ laying on the bottom of the tank; exposed fin rays; blood on edge of fins; skin ulcers; cloudy eyes

Possible Causes: Bacterial infection brought on from bullying and/or fin nipping; Poor water quality

Fin Rot Treatment: More frequent water changes; separate the bully from the rest of the fish; Tetracycline mixed with dry food

Fish Fungus

blue german ram fungusPossible Symptoms: Initially you will notice a gray or white-ish growth in and on the skin and/or fins; cotton like growth

Possible Causes: Fungus is usually secondary to parasites, a physical injury or bacterial infection that went untreated. Poor water quality could also be a cause.

Fish Fungus Treatment: API Fungus Cure or any other fungus remedy and more frequent water changes.

Gill Flukes

gill flukesPossible Symptoms: Infected Gills; Strong breath

Possible Causes: Stress from incompatible tank mates; poor water quality; overcrowding.  Gill Flukes are flat worms approximately 1mm long

Treatment: Tetra Parasite Guard or any other Parasite medication like Prazipro.

Gill Mites

Gill MitesPossible Symptoms: Gasping at the water surface; gill covers are partially open

Possible Causes: Infections brought on from new fish

Treatment: Tetra Lifeguard

Hemorrhagic Septicemia

Hemorrhagic SepticemiaPossible Symptoms: Hemorrhaging of internal organs, skin and muscles; bulging eyes; bloated stomach; bruised looking or redish tint to eyes, skin, gills, and fins; open sores; abnormal behavior

Possible Causes: Introduction of a fish already infected with the deadly virus called Viral Hemorrhagic Septicemia Virus

Treatment: No none cure

Hole In The Head (HITH)

Aka Head and Lateral Line Erosion (HLLE)

Hole In The Head freshwater fish diseasePossible Symptoms: small holes or indentations on the head of the fish; markings along the lateral line; may stop eating

Possible Causes: Parasite; poor water quality; lack of proper nutrion

Treatment: More frequent water changes; keep parameters in check for you specific fish needs; Possibly Seachem Metronidazole


IchthyosporidiumPossible Symptoms: Sluggishness; loss of balance; hollow belly; external cyst or sores; yellowish brown nodules

Possible Causes: Feeder crustaceans in particular transmit the disease

Treatment: No definitive cure is known for this disease. Some have had success with Phenoxethol or Chloromycitin added to dry food. Many say to euthanize the fish affected as soon as signs start showing to hopefully prevent entire stock being destroyed by the disease.

Ick or Ich

ick betta fishPossible Symptoms: White spots on the body and fins of the fish that resemble sand or grains of salt; scratching against objects; clamped fins; gasping at the top of the water surface

Possible Causes: Poor water quality; introduction of another fish with Ich; stress from factors such as rapid temperature change, pH fluctuations, overcrowding, bullying, fin nipping

Treatment: More frequent water changes; keep an eye at least once a week on water parameters; Increase temperature in the tank to 82 degrees F and use any Ich treatment. The water temperature will help to speed up the life cycle of Ich.


Leeches in fishPossible Symptoms: Heart shaped parasites attached on the fish

Possible Causes: Usually brought into the tank from plants and snails. Could also possibly be brought in from pond fish

Treatment: Bathe in an Epsom Salt bath for 15 minutes. Most leeches should fall off from this bath. Those that do not you will have to use tweezers to pull the remaining off of your fish causing minimal harm to your fish. Your fish will have open sores so it is best to perform a water change before adding your fish back to ensure the best possible water quality and to prevent secondary infections.

Lice or Louse

Lice or Louse infected fishPossible Symptoms: Fish are aggravated and restless; rubbing/scratching on objects in the tank; Lice have 8 legs that resemble tiny pale crab. Looks like tiny oval dots moving on your fish.

Possible Causes: Wild fish or fish from a pond that where brought into aquariums

Treatment: Physically remove the lice

Neon Tetra Disease

Neon Tetra DiseasePossible Symptoms: Whitened areas deep in the flesh; muscle degeneration; restlessness; pale in color; difficulty swimming; body may become lumpy

Possible Causes: Feeding on dead fish with the disease; feeding of live food such as Tubifex

Treatment: To date there is no known treatment for this disease. Even though it is called Neon Tetra Disease, it can also affect other fish not even in the tetra family. Best solution is to remove and humanely put down the infected fish as soon as symptoms start to show to prevent infection of other fish.

Nitrite/Nitrate Poisoning

nitrate poisoningPossible Symptoms: Lethargic fish; Resting just below water level

Possible Causes: Poor water quality; Not enough filtration for bioload; overstocked; mini-cycle occurring

Treatment: Perform immediate partial water change and increase number of water changes performed on regular basis.

Oxygen Starvation

fish oxygen starvationPossible Symptoms: Fish at surface of the water; gulpig at water surface

Possible Causes: Water temperature too hot; Lack of proper aeration

Treatment: Check the temperature of your water and turn down the temperature if needed. Be sure to research your specific fish breed to ensure you have the proper temperature for that particular breed.  Use airstones or powerhead to increase circulation in the tank which will provide more oxygen to your fish.  Check your filter to make sure it is not clogged or full of food from the fish tank. If it is clean the fish tank filter and/or change the filter.

Pop Eye

Pop Eye fishPossible Symptoms: One or both eyes may be protruding or appear as though they are popping out; area around the eye may be inflamed and discolored

Possible Causes:  Bacterial Infection; Poor Water Quality

kanaplexTreatment:  Check water parameters first to make sure that they are within the range for your species of fish. If all water parameters are within range then you can treat the tank with Tetracycline.

Ragged Tail Fin

Ragged Tail FinPossible Symptoms: progressive deterioration of the tail and/or fin; frayed fins; color fading

Possible Causes: A bacterial infection; Being bullied; an injury from fin nipping, poor water quality.

Treatments: Check water parameters and do a partial water change if they are not within range. If water is good and pop eye is still present you can treat your aquarium with Tetra Lifeguard.

Red Pest

Red PestPossible Symptoms: Bloody streaks that appear on the body, fins, and/or tail; ulcerations’ possible fin and tail rot; loss of fin and tail in severe cases

Possible Causes: Internal Bacterial Disease

Treatment: External treatments do not work will with this infection. A bacterial antibiotic added to dry flake food should work well in this case.

Swim Bladder

Swim Bladder disease golden fishPossible Symptoms: Erratic Swimming; Unable to stay upright; swimming on the side; Sinking to the bottom of the tank

Possible Causes: Gulping too much air: overeating; enlarged intestines from constipation; impacted eggs in females

Treatments: Shelled frozen peas thawed. Can also not feed fish for several days. Do a partial water change.


kanaplexPossible Symptoms: Emaciation; hollow belly; sore; lethargic fish; skin ulcers; frayed fins; fin and scale loss; loss of appetite; yellowish or darker nodules on eyes or body and possibly deform fish

Possible Causes: Overcrowding in poor water conditions

Treatment: No absolute treatment as of now. However, Kanamycin and B-6 for 30 days may be effective.  Kanamycin can be purchased in local pet store or on Amazon.  B-6 can be obtained from liquid baby vitamins (one drop per 5 gallons of water)


velvet infectionPossible Symptoms: Similar looking to Ich but shows as smaller yellow or dusty gray spots; rapid fill movement; rubbing on objects in tank; clamped fins; respiratory distress; eye cloudiness; possible weight loss

Possible Causes: Parasite

aquarisol for fish treatmentTreatment: Aquarisol works for Ich and Velvet if there is any doubt as to which your fish may have.

Fish Medicine

It is always important to examine your fish at least once a day closely to prevent and catch illnesses earlier.  Learn their behavior as each fish is different. A good rule of thumb is if you have a sick fish, and you need fish medicine, do at least a 30% water change before adding in any fish treatments. The cleaner the water the better chances your fish have to fight the infection or illness and recover faster. There are several important things you can do to possibly prevent most of the common infections and illnesses in freshwater fish tanks.

  1. Always cycle your new fish tank. This will prevent sudden spikes in the water chemistry which could have life or death effects on your fish.
  2. Make sure your tank is not overstocked. The rule is one gallon of water per inch of fish. Just because your tank says it is a 20 gallon tank does not mean you have 20 gallons of water in there. Once you add the heater, filtration, airstones, substrate, and decorations you lose several gallons of water.
  3. Make sure that all of the different types of fish you are adding to your fish tank are in fact compatible with each other. Take Cichlids for example. They have two different groups of Cichlids which is not a good idea to pair together. However, within each group you have semi-aggressive and aggressive species. It would not be wise to pair aggressive and semi-aggressive species together. It is vitally important to research all fish you are wanting to add to your aquarium before you get them so you will maintain and keep healthy fish tank. Check to make sure they all need the same water parameters and temperatures. A fish that does well in lower temperatures will not pair well with one that requires higher temperatures.
  4. Water changes are so very important. Imagine living inside of your toilet and this means eating, using the bath room, reproducing, and sleeping. This is the equivalent to your fish tank. They live, reproduce, breath, eat, and poop inside of their aquarium. They do not always eat all of the food that is given to them just as us humans do not always eat all of the food on our plates. Uneaten food causes ammonia which means your fish are not going to be healthy. Check your water parameters often, especially the ammonia to ensure your fish are in the healthiest living situation you can give them. Remember to not only change the water but to vacuum the substrate also. This will help remove excess food left behind and most if not all fecal matter that your fish has produced which will help get your water parameters in check.
  5. The less chemicals you can add to your fish tank the better your fish will be. Should you notice anything wrong or different with any fish, check your water parameters first and do a partial water change to see if this will help. Wait at least 12-24 hours if possible before deciding to add anything to the fish tank. Many different conditions can be traced to poor water quality and it will take some time after a water change to see if it will help the situation.
  6. Always know how many fish you have in the fish tank and keep track of them daily. A dead fish decaying in the tank is super unhealthy and can pose many health risk to your fish especially if they died from a disease and other fish are eating on them. Would you want to live in your home with a decaying body?
  7. Check all live fish tank plants. Dead leaves and stems decaying in your tank will throw your water parameters off and cause spikes which are unhealthy for your fish. Remove dead or dying leave and stems as soon as you see that they are dying to help prevent any spikes in your tank.
  8. ALWAYS quarantine all new fish, invertebrates (snails, shrimps etc.) and plants. Rare illnesses can take up to 12 weeks before most aquarist will notice that there is anything wrong with the fish. A quarantine fish tank separate from your main fish tank with similar water parameters and temperatures is a must if you want to add new anything to your tank and not risk infecting the stock you already have.
  9. A high quality food for your fish is also best. Research your fish diet needs and ensure that you are feeding them the best food possible and that you are giving them different foods periodically. Always feeding them flake food would be equivalent to you eating a chef salad everyday for every meal. Gets very boring and bland after a while. If you have a fish that is strictly a carnivore, a flake food diet is not going to be enough nutrition for your fish and will reduce its health. Do your research and learn everything you can. You would be surprised all that you can learn.
  10. When trying to diagnose an illness or a problem with your fish, make sure you check out more than one particular illness or disease as many can have similar symptoms but be slightly different and the treatments may be different also. Use as many different keywords with as many symptoms as you notice to best determine what is possibly going on with your fish and so you can treat it correctly the first time. Also, do not depend on only one website to give you an answer.  Check many different ones and choose for yourself which option you should go with as many illnesses and disease could possibly be treated with many different medication.