Killifish Diseases

Common Killifish Diseases and Treatments

      Even freshwater fish need salt and minerals to be healthy.  Therefore having aquarium salt on hand at all times is a good idea for so many reasons.


    As general information, remember that salt doesn't evaporate, so don't add more salt, if you are just adding water.   Add salt in proportion to the amount of water you replace in your weekly water change.  A good rule of thumb is 1/2 tsp. of aquarium or seasalt per gallon of water.   If you use tap water, remember to  let it sit 24-48 hours so that all of the chlorine dissipates. 


    Also, if you treat with a commercial medication, remove the filter, but do leave an airstone running.  Filters will remove the medications and chances are that the fungus or bacteria that is effecting your fish, also has a large population culture thriving in your filter medium, where particulates collect.  Wash and replace filter and medium after medication dosage is complete.  A 25% - 50% water change after the treatment period isn't such a bad idea either.

Need a product to treat your fish?  Visit our "Ph'ish Pharmacy".


                                            Symptom Potential Causes & Treatments


New fish are sluggish, won't eat, hide, & are generally distressed.


      1)  Acclimation Shock - differences in water chemistry, temperature, and shipping shock.

    2)  Check water conditions and very slowly add about 1/4 tsp. of aquarium salt/gal, or "StressCoat" per instructions.

     3)  Environmental Change Shock

         A.  Just let nature take its course and have plenty of plants for hiding.  Fish will eat when they're hungry & when you're not watching.

     4)  General Behavior of Species of Fish
          A.   Check with aquarium books & references to learn more about this species.

           B.  Introduced new fish to tank with predators.4) Isolate new fish and check for compatibilities.


Sudden loss of many fish over a short period of time, with few preceding symptoms. Other fish stay near the top/ bottom and may lose balance. They are dull in color & activity and don't eat.  Catfish dies.


     1) Toxic Shock, usually from ammonia, nitrates, nitrites, pH, or other poisonous chemicals.

Water should be tested for ammonia and related, changed slowly (1-2 hrs.) if necessary.  Check fish for other symptoms.

     2) Low Dissolved Oxygen Levels.  Make sure filter is working and add an airstone to add more diffused oxygen.

     3)  Virus or Bacterial Disease Infections.

     4)  Check fish for possible other symptoms.


Fish rub against glass or plants quickly and "flash" when they turn to rub their sides exposing their bellies.  Attempt the "Dramatic Darwin Leap".


     1) Chemical irritation of the skin or gills, caused by raised levels of ammonia, nitrite or very high/low pH.

         A, Water should be tested for ammonia and related, changed slowly if necessary.  

        B.  Check fish for other symptoms. 

        C.  A little "StressCoat" may help.

   2)  Irritation caused by external parasites such as flukes, fungus, Trichodina, white-spot etc on the skin or gills.

        A.  Scraping the skin or gills gently to remove parasites, add 1/4 tsp. aquarium salt/gal.


Fish swim normally but appear to be breathing heavily.  Fish appear to be gasping, they may crowd water inlets


1) Hypoxia. Dissolved oxygen levels may be low.
   A.  Test water and check filter to make sure it isn't clogged.  

    B.  Add an airstone.

2)  Poor water quality causing gill hyperplasia, excess mucus production or nitrite toxicity.

    A.  Check filter to make sure it isn't clogged. 

    B.  Test for ammonia, nitrite levels and pH

3) It could indicate the early stages of gill disease.

     A.  Treat with 1/2 tsp. seasalt/gal or  

     B.   1/2 dosage of commercial products

4) Gill parasites.

     A.  Scrape gills gently to remove parasites,

     B.  add 1/2 tsp. seasalt/gal, or treat with commercial products


Individual fish stays apart from others. Breathing is normal. They may refuse food.  They may have "cloudy" or gray areas on the skin


1)  Common symptoms of many diseases, so further investigation is essential

     A.  Observe closely & test water.

 2) Fish may be suffering from a parasite problem.

     A.  Take a skin and gill scrape. Examine the gills.

     B.  add 1/2 tsp. seasalt/gal, or treat with Jungle Labs Parasite Clear or other commercial products

  3)  There could be internal disease problems

       A..  Add 1/2 tsp. seasalt/gal, or treat with Maracyn 2  or other commercial products

B. Early stage of systemic bacterial infection

    C.  Isolate and observe


Several fish are sluggish. Fish won't eat or eating very little. Fish are skittish and shy. Some fish may have split or ragged fins


1)  Common symptoms of many diseases

    A.  Test water for ammonia, nitrite, pH.2) High levels of organic pollution.

    B.  Check & Change filter.

2) External parasite infestation.

    A. Take a skin and gill scrape. Examine the gills. 

    B.  Add 1/2 tsp. seasalt/gal, or treat with Jungle Labs Parasite Clear  or other commercial products

3 Early stage of bacterial disease.

    A. Check fish for lesions, inflammation and ulcers

Excess of gill and/or skin mucus. Grey slime/ trailing mucus.  May be accompanied by rubbing/flashing, heavy 'breathing' and/or sluggishness.  

  1. Water chemistry problems.

      A. Test water for ammonia, nitrite, pH.

  2) External parasites.
     A.  Take a skin and gill scrape. Examine the gills. 

     B.  Add 1/4 tsp. seasalt/gal, or treat with Jungle Labs Parasite Clear or other commercial 


Skin lesions or ulcers.  Reddening or inflammation on the body or fins. Raised scales. Area swelling. Open wounds or lesions that do not heal within a day or two.


  1) Physical injury. This will normally present as a 'clean' wound with little swelling or filmy growths.

     A.  Watch for infection.   

     B.  Add 1/4 tsp. seasalt per gal. for infection prevention, or treat with MelaFix™, Aquarium Pharmaceuticals
E.M. Tablets, or similar

2) Local tissue irritation caused by external parasite infection.

     A.  Take a skin and gill scrape.                

     B.  Examine the gills. 

     C.  Add 1/2  tsp. seasalt/gal, or treat with Jungle Labs Parasite Clear or other commercial products3) Bacterial disease

3)  Check fish for possible other symptoms.  

     A. Add 1/2 tsp. seasalt/gal, or treat with Maracyn or other commercial products (antibiotics & sulfa drugs)

4) Water quality problem.
    A.  Test water conditions

     B.   very slowly add about 1/4 tsp. of seasalt/gal, or "StressCoat" per instructions

    5) High levels of organic pollution.

         A.  Check & Change filter.
        B.  Change at least 20% water

  5)  Localize red or white lesions on the body  Larger external parasites such as lice, leeches or anchor worms

         A.  Treat with Jungle Labs Parasite Clear  or other commercial products such as ParaGuard by Seachem $4.99 at PETsMART effective and inexpensive treatment for ectoparasites and external fungal, bacterial, & viral infections


Fin rot, frayed, split or ragged fins. Possibly with white fuzzy edge and some reddening of the fins


1) Bacterial infection
   A. Check fish for possible other symptoms.  

    B.  Add 1/2 tsp. seasalt/gal, or treat with commercial products (MelaFix™, antibiotics & sulfa compounds)

 2)  Ectoparasite infection.

      A.Treat with commercial products (antibiotics & sulfa compounds

 3) Poor environmental conditions.

       A.  Check water and filter.

  4)  Physical damage

       A.  Add 1/2 tsp. seasalt/gal and a little "StressCoat"

  5) Over crowding

      A.  Keep the 1" of fish/gal. of water rule of thumb.

  6) Saprolegnia (fungus) infection

      A.  Fungus Cure Capsules from Aquarium Pharmaceuticals

  7) Columnaris infection (mouth fungus/cotton wool disease)

      A.  Triple Sulfa™ Capsules or MelaFix™ from Aquarium Pharmaceuticals


Fish has swollen abdomen (dropsy).   Possibly raised scales and some reddening on the body or fins.  Possibly pop-eye (exophthalmos)


1) Viral infection.
   A. just like the common cold, often not much to do but reduce stress.

2) Systemic bacterial infection. leading to 'dropsy' (build up of fluid in the abdomen. Can be differentiated from tumor by shape, symmetry and feel (feels soft and fluidy)

  A. Tetracycline from Mardel Labs   $5.79/24 capsules at PETsMART

3) Neoplasm (tumor). Can usually be determined by size, shape
(usually asymmetric) and palpation (feeling - usually hard)

   A. Plan to replace fish.

4) Heart or kidney disease. Can only be diagnosed by postmortem

   A.  Plan to replace fish.

5) Internal parasites (endoparasites)
    A.  Maracyn-Two from Mardel Labs capsules at PETsMART

  6) Genetic disorder
     A. Plan to replace fish with one from different stock to strengthen gene pool.

  7) Intestinal blockage

       A.  Plan to replace fish, but if caught early enough, feeding brine shrimp may help. 


Respiratory problems. Gill examination shows areas of necrosis (dead tissue), mottled appearance, heavy mucus


  1) Bacterial gill disease

     A.  Check fish for possible other symptoms.  

    B.  Add 1/2 tsp. seasalt/gal, or treat with commercial products (antibiotics & sulfa drugs).

  2) Viral infection
     A.  Just like the common cold, often not much to do but reduce stress.

3) Branchiomyces (gill rot)

     A. Furan-2™ Capsules or other commercial products (antibiotics & sulfa drugs)

4) Gill parasites.

    A.   General Cure™ Capsules from Aquarium Pharmaceuticals


Tiny white spots, as though fish has been sprinkled with salt. Usually with thickened mucus

1)  Ichthyophthirius - "Ich"

     A.  Darken the tank.  Ich needs light.  

     B.  Treat with Aquarium Salt

     C.  Various effective products are available for "Ich"

     D.  Raise aquarium temperature


White or or grayish 'cotton-wool' patches on the skin or fins. Often accompanied by inflammation and skin erosion


1) Saprolegnia (fungus) infection

    A.  Fungus Cure Capsules from Aquarium Pharmaceuticals

 2) Columnaris infection (mouth fungus/cotton wool disease).

     A.  Triple Sulfa™ Capsules or MelaFix™ from Aquarium Pharmaceuticals


Swellings on the skin


1)  Parasitic cysts.

    A. Take 'deep' skin scrape

2) Physical injury or battle wound

    A.  Examine fish and observe. 

3) Bacterial infection. Usually accompanied by inflammation and raised scales.

    A. Examine fish for inflammation and/ or raised scales.  

    B.  Add 1/2 tsp. seasalt/gal, or treat with commercial products (MelaFix™, antibiotics & sulfa compounds)4) Internal tumors

4) May be harmless, but plan to replace fish.


Growths on skin/fins Tumors or viral infections such as;


1) 'carp pox', which resembles melted wax poured over the fins or skin

2) papillomas, 'warty' types of growths, can be quite large, smooth or cauliflower-shaped, white, red or pink

3) lymphocystis, various sized, white to pink masses on the skin and/or gills.

   A. There are no certain and specific treatments for these growths. They are usually benign and often self-resolving. Check fish for possible other symptoms.  

   B.  Add 1/2 tsp. seasalt/gal, or treat with commercial products (antibiotics & sulfa drugs)

There is always the risk of secondary bacterial infection.  Although raising salinity may help, a wide range medication, such as Maracyn-Two from Mardel Labs capsules at PETsMART may prove helpful.


Corneal Opacity (cloudy eye)


1) Physical injury

    A.  Add 1/2 tsp. of seasalt/gal, or 

    B.   treat with commercial products (antibiotics & sulfa drugs)

2) Nutritional deficiencies
   A Vary diet, with emphasis to feeding brine shrimp and/or live foods.

3) Poor water quality

    A. Check water conditions and 

    B.  very slowly add about 1/4 tsp. of aquarium salt/gal, or "StressCoat" per instructions.

4) Bacterial infection
   A.  Check fish for possible other symptoms.  

    B.  Add 1/2 tsp. seasalt/gal, or 

    C.  treat with commercial products (MelaFix™, antibiotics & sulfa compounds)


Loss of balance with fish unable to stay upright. Fish may be able to maintain position when swimming, but turn over when they stop swimming.


1) Swim-bladder disorder / disease caused by viral or bacterial infection, constipation (mainly fancy goldfish) or other organ disease.

  A.  Add 1/2 tsp. seasalt/gal, or 

  B.  treat with commercial products (MelaFix™, antibiotics & sulfa compounds)

  2) Internal organ disease, i.e. kidney / intestinal disease or blockage.

     A.  Plan to replace fish

Sluggishness, weight loss, and fish loss. Worms protruding from anus


1)  Internal parasites (endoparasites). 

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