S a l t w a t e r  F i s h  D i s e a s e s

This is a glossary of common diseases which infect marine fish and other vertebrates. Although not every disease is treatable--or easily diagnosed, this list should serve as a basic aid in diagnosing and treating ailments.

Table of Contents

  1. Marine Ick/White Spot
  2. Marine Velvet
  3. Black Spot
  4. Intestinal Worms
  5. Microsporidian Infection
  6. Bacterial Fin Rot
  7. TB/Wasting Disease
  8. Vibriosis
  9. Lympocystis
  10. Ichthyophorius
  11. Head and Lateral Line Erosion
  12. Poisoning

Marine Ick

This common marine parasitic disease is also referred to as white spot, and is caused by the marine parasite Cryptocaryon Irritans.  The symptoms usually involve granular, sand-like spots (about 1 mm in diameter).  Fish are often found scratching themselves against rocks and other objects in an attempt to remove the parasite.  There are many effective remedies available to treat this disease, many of which are copper based.  There are also medications that do not contain copper, and are invertebrate-safe.  This disease has the affinity to lay spores in the substrate, so preventive medicines are also effective in Ick control.

Marine Velvet

A parasitic disease which symptoms are similar to that of marine Ick.  Caused by the parasite Amyloodinium Ocellateum.  The infected have sandpaper-like skin, with small gold/brown spots covering the body.   Fish are often found scratching their bodies against various objects trying to remove the parasites.  Treat with a parasitic medication, and/or perform a freshwater dip for 3 to 10 minutes.

Black Spot/Gill and Skin Parasites

Parasites that will actually appear in different physical characteristics.  Signs of this disease include gasping/coughing, scratching, white patches, and/or visible long dark worm-like attachments.  It is caused by hosts of different parasites, and is often treated by a long bath in parasitic remedies such as Methylene Blue or Formalin.  This disease can also be effectively controlled by preventive type medicines that disallow the spreading of this deadly disease.

Intestinal Worms

Caused by a number of different internal worm parasites (ie roundworms and tapeworms).  The symptoms include an overall change of color, erratic swimming, distended stomach, and emaciation.  Because of the variation of parasites that cause this, and the fact that they primarily strike internally, it may be difficult to identify exactly what the infliction is.   Treat with a general parasitic medication for worm parasites.

Micrsporidian Infection

Signs of this parasitic disease include white patches, erratic swimming, loss of appetite, emaciation, and listlessness.  Often caused by the protozoa Pleistophora species.  Unfortunately, there is no known cure for this disease.  The best thing to do if this is positively identified is to separate the fish into a quarantine tank away from other possible victims.

Bacterial Fin Rot

Another disease brought on by poor water conditions, this bacterial infection is identified by a reddening of the base of the fins and anus.  Fins are often found closed, frayed, or decaying.  It's best to test the water to identify the stressor,  and/or look for physical signs of stress.  Once the stressor is removed and the disease is identified, treat with a medication for bacterial infections.

Wasting Disease (Marine Tuberculosis)

Disease caused by a bacterium that is transferred either by ingestion of infected material or via open wounds.  The symptoms include fin erosion, ulcers/holes, loss of appetite, reddened areas, and listlessness.  If this disease is not diagnosed early, it often develops very quickly and is terminal.  Treat with a general bacterial medication.  It is best to quarantine the affected fish, as it is with many of these diseases.


Usually brought on by poor water quality and stressful conditions.  Vibrio is only a pathogen when stress allows infection from the gut or via wounds.  Physical symptoms include darkening of color, loss of appetite, reddened areas, listlessness, or abdominal swelling.  Thankfully, this is not a common disease because treatment is difficult.  It is best to use a bacterial medication containing the chemical Furanace or Erythromycin.

Lymphocystis (Cauliflower Disease)

Caused by the virus Lymphocystis, this disease is fairly easily identified by the warts/lumps that spread over the body.  The virus enters through lesions, and is passed on from disintegrating old tissue.  Oftentimes the affected fish's own immune system will allow the fish to recover from this ailment.  However, this may take several months.  Treatment should include quarantine.


A fungal infection usually brought on by cysts that are taken in orally by eating fish feces or cannibalizing dead fish (yuck!)  It's symptoms include an overall change of color, loss of appetite, listlessness, and skin that appears like sandpaper.  This is another disease that can be difficult to treat.  It's best to identify in it's early stages, and treat with an anti-fungal medication.

Head and Lateral Line Disease

A disease brought on by poor water quality, nutrient deficiency, or possibly parasites.  Some aquarists argue that stray electrical currents in the aquarium water from electrical devices can also bring this on.  The symptoms include ulcers/holes in the head area, and/or erosion of the lateral line along the dorsal side of the fish.  It's best to make an attempt to improve aquarium water conditions, dose food with vitamins, ground electrical currents, or medicate with Flagyl (a freshwater remedy for hole in the head).


Caused by a variety of stressful components which are introduced to the aquarium water.  Some of these include, overfeeding, overdosing, using incompatible medications, heavy metals, or household cleaners.  Symptoms often include gasping/coughing, change of color, cloudy eyes, erratic swimming, or loss of appetite.  This requires immediate removal of livestock to unpolluted water or the pollutant removed with water changes.

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