Lymphocystis Disease of Fishes
Adrian Lawler, Ph.D.
(retired) Aquarium Supervisor (l984-l998) J. L. Scott Aquarium Biloxi, Ms 39530
Original to Aquarticles
Lymphocystis is an infectious viral disease of freshwater and saltwater fishes that causes
cell enlargement (many more times than normal cell size), also called hypertrophy, usually
on the skin and fins. The enlarged cell nodules may each reach 0.3 mm to greater than 2.0
mm in diameter, each becoming a virus factory. Lymphocystis is the most common viral
infection of aquarium fish, and has been reported in over 125 species of freshwater and
The disease usually runs its course in 4 or more weeks (depending on species involved,
water temperature, and other variables) and then the enlarged cells rupture or slough off
and release the viral particles into the water. While infected, the fish may become slowed
or weakened, or more visible, and thus be more prone to predation or attack. If there are
mouth lesions, the fish may have difficulty in feeding or may not be able to feed. The low
mortality rate some attribute to lymphocystis is mostly due to secondary bacterial or
fungal infections. I have worked with many thousands of fishes of various freshwater and
salt water species and do not recall a single death being directly due to a lymphocystis
After lymphocystis lesions are lost, the host tissue heals up. Adhesions and scarring
can occur during healing. If the gills are affected, the fish can have difficulty
breathing, especially if gill surface areas are destroyed (no longer present), or
adhesions or scarring occur and gill surfaces are thus reduced in surface area or
functional quality for oxygen uptake.
The viral particles in the water can go on to infect another fish of the same or
closely related species. I suspect the virus can also become dormant and remain viable in
sediments for years. The virus may be stored for years (for future research) by either
freezing or freeze-drying the separated viral particles, infected tissues, or infected
The disease poses no known health hazard to humans. To decrease spreading this disease
to other fishes, infected fish should be buried or burned, and not thrown back into the
The viral agent of lymphocystis disease is an iridovirus (of the family Iridoviridae)
called Lymphocystivirus (genus name). Iridoviruses range from 120-300 nm
(nanometer = one billionth of a meter) in diameter. Iridoviruses have an icosohedral or
20-sided shape, and a DNA core.
I have worked on the disease in silver perch (Bairdiella chrysura),
white-tailed damselfish (Dascyllus aruanus), black-tailed humbug (Dascyllus
melanurus), copper banded angelfish (Chelmon rostratus), Koran angelfish (Pomacanthus
semicirculatus), Moorish idol (Zanclus canescens), foureye butterflyfish (Chaetodon
capistratus), orbiculate bat fish (Platax orbicularis), queen angelfish (Holacanthus
ciliaris), and warmouth or goggle-eye (Lepomis gulosus).
Lymphocystis does show some host-specificity, i.e., each strain (or species) of
lymphocystis can infect only its primary host fish, or some additional closely related,
DNA studies have showed that there are different species of the virus. This has been
suspected for some time because the viral particles from different fishes vary in size
plus the virus from a fish usually will infect only that species of fish or a few other
species closely related to the primary host.
The virus enters through broken skin or injured tissue (usually skin or fin). If the
virus gets into the blood (usually via gill infections) then various internal organs can
be infected. In l974 I showed that the spleen, tissues behind the eye, eye, and many other
internal organs can be infected via systemic infection. One can easily infect fish by
putting them into a bucket of water, introducing the virus, then injuring fish by
vigorously swirling a stiff bottle brush in the bucket. One can also run a sharp probe on
the skin or tail (see warmouth picture below) and expose the fish to the virus to infect
Incubation times (until lesions are visible to eye) range from about 10 days at 25 C to
longer, depending on species involved, temperature, and other variables.
Important or valuable affected fish should be isolated and monitored for secondary
bacterial or fungal infections that should be treated with appropriate drugs.
In 1979 I discovered that goggle-eye (warmouth), when subjected to heavy rains and
sediment loads, came down with lymphocystis. It is unknown, in this case, whether stress
or physical injury led to the lymphocystis infections. Stress to the fish, in this case,
could be from exposure to sediments in the water leading to breathing problems, from
getting tired trying to maintain their position in the swift water, from being exposed to
toxins swept in by the water, etc. There is also the possibility that sediment or debris
particles hitting the fish in the swiftly moving water caused injury that led to the
infections (similar to injuring fish in a bucket by swirling a brush).
There is no way to cure a viral disease in any organism yet, no matter what some of the
fish medications claim. Some virus diseases in various organisms can be prevented by
vaccination, or slowed down by medications. There is no vaccine for lymphocystis yet.
Some medications claim to cure lymphocystis in several days to a week. However,
depending on the stage of the disease, many enlarged cells will burst and disappear on
their own (without using the "cure"), making some think their chemical has cured
the disease. One can also excise the enlarged cells, affecting an apparent
"cure," but, in reality, just removing most of the infected cells (which then
can no longer be seen). Lymphocystis cannot be "cured."
Lymphocystis, once acquired, must run its course. There are some ways to decrease the
chance of fish getting the disease:
Handle fish carefully to reduce injury to skin and fins and slime coat.
Reduce or prevent stress on the fish. Stress would include overcrowding, starvation,
overfeeding, sudden environmental changes (temperature, salinity, pH, DO, strong currents
carrying debris, etc), toxins (pesticides used nearby; high ammonia, nitrite, or nitrate),
or anything else that could affect the immune system or cause physical injury.
Lymphocystis frequently appears on the tail due to nipping by other fish, usually a result
While I was working on this disease in silver perch, I suddenly had numerous warts
appear on my hands. I handled many experimentally infected fish. I could get no doctor to
excise a wart and compare the wart virus with the lymphocystis virus I was working on, so
I leave the answer to this question to those in the future. Several months later, shortly
after I worked in concrete (a basic pH medium) building a concrete pond, the warts just as
mysteriously disappeared, and remain gone over 30 years later.
Did I find that lymphocystis can infect humans? And that warts can be cured by abrasion
and/or a basic solution? Only the future work of others will tell.
Dukes, T. W., and A. R. Lawler. 1975. The ocular lesions of naturally occurring
lymphocystis in fish. Canadian Journal of Comparative Medicine, 39 (4): 406-410.
Howse, H. D., A. R. Lawler, W. E. Hawkins, and C. A. Foster. 1977. Ultrastructure of
lymphocystis in the heart of the silver perch, Bairdiella chrysura (Lacepede),
including observations on normal heart structure. Gulf Research Reports, 6 (1): 39-57.
Lawler, A. R., H. D. Howse, and D. W. Cook. 1974. Silver perch, Bairdiella chrysura:
New host for lymphocystis. Copeia, 1974 (1): 266-269.
Lawler, A. R., J. T. Ogle, and C. Donnes. 1977. Dascyllus spp: New hosts for
lymphocystis, and a list of recent hosts. Journal of Wildlife Diseases 13 (July, 1977):
Lawler, A. R., J. T. Ogle, and C. Donnes. 1978. New hosts for lymphocystis. Gulf
Research Reports 6 (2): 183-184.