The Lymphocystis Virus in Saltwater Aquarium Fish

Clownfish with Lymphocystis


Lymphocystis is a chronic disease of freshwater and marine fishes caused by infection with an iridovirus known as Lymphocystivirus or Lymphocystis disease virus (LCDV), which is a member of the family Iridoviridae. Infection appears on the infected fish as one or more white or beige colored pebble or wart-like nodules most commonly seen on the fins, skin, or gills, although other tissues may be affected. You can see a sample of the Lymphocystis Virus in these photos on

Lymphocystis may also be the root cause of what appears to be "Popeye" in fish which have infected tissues behind the eye, which causes the eye to protrude as the infection progresses and increases in size.

"The Lymphocystis nodules are clustered groups of greatly enlarged, infected cells known as fibroblasts, which are part of the connective tissues in the fish (Figures 3 and 4). These infected cells are 50,000–100,000x larger in volume than normal cells because they have become "virus factories," using the infected cell's machinery to produce more virus, and thus are filled with virus particles. After these "virus factory cells" have completed their production of virus particles, the cells will burst and shed virus into the environment." (Description from the "Lymphocystis Disease in Fish" article by Roy P. E. Yanong, VMD at the University of Florida)

Lymphocystis is a somewhat common infectious virus hosted by freshwater and saltwater fishes which causes cells to enlarge many times their normal size. It is usually found in the fish skin and fins. After residing on its host for 4 weeks or more, the Lymphocystis cells rupture or fall off the host, spreading the infected cells in the water. The cells then either sink to the bottom of the tank and lie dormant or reattach to another host via a break in the skin or fins, or in the gills.

The good news is this virus is unique and is fairly easy to identify, and death from the virus itself is fairly rare. When the virus first begins to grow, it may be confused with the parasites Cryptocaryon irritans (marine white spot disease), appearing as small white or off-white specks on the fish's skin or fins.

The bad news is Lymphocystis, at present, has no known cure and there no known method for destroying the virus in its free-floating stage.

The Lymphocystis Virus

  • Appears to be contagious, spreading to other fish of the same or closely related species.
  • The virus enters the fish's body through openings (injuries) in the fins, skin, and gills.
  • Spreads fairly rapidly on the affected fish.
  • Death is usually caused by secondary bacterial or fungal infection.

According to the scientists at National Fish Pharmaceuticals:

  • These growths may be surgically removed, but this is certainly no cure.
  • This virus will become systemic and show up in larger numbers when it comes back again.
  • This virus can spread like cancer throughout the fish.

They further say that: "Some people state that Acriflavine will cure this virus. This is false info."

Unfortunately, with no known effective cure/treatment, the outlook for a cure for this virus isn't very rosy at this time. It appears that prevention and quick identification are the best courses of action.


  1. Closely examine new arrivals for signs of infection.
  2. Quarantine all new arrivals.
  3. Don't obtain specimens from known infected sources.


  1. Isolate all infected fish in a Quarantine Tank.
  2. Feed a healthy diet, including supplements.
  3. Treat for secondary infections.

If you wish to sterilize a tank that has been infected with the Lymphocystis virus, it has been found that it can be inactivated with any of the following compounds, after 15 minutes at 77°F (25°C): potassium permanganate (100 mg/L or higher), formalin (2000 mg/L or higher), or sodium hypochlorite (liquid bleach—various formulations) at 200 mg/L or higher.

In the end, dealing with Lymphocystis is much the same as with any other contagious disease in a marine aquarium. With proper precautions, care and treatment, the affected fish should survive, and the other critters in your tank will not be adversely affected.

Article Sources
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  1. López-Bueno, Alberto et al. Concurrence Of Iridovirus, Polyomavirus, And A Unique Member Of A New Group Of Fish Papillomaviruses In Lymphocystis Disease-Affected Gilthead Sea BreamJournal Of Virology, vol 90, no. 19, 2016, pp. 8768-8779. American Society For Microbiology, doi:10.1128/jvi.01369-16

  2. Lymphocystis Disease in Fish. University of Florida Institute of Food and Agricultural Sciences Extension