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Having encountered elsewhere in The Hopstial a case where there existed the possibility of confusion in some borderline cases between Ich and a disease called Lymphocystis, I thought I'd dig up the old TFH back number and cover the article, in my own inimitable literary style.

Lymphocystis Disease

First of all, the causative organism. Lymphocystis is caused by a virus, known as Lymphocystivirus, belonging to the Iridoviridae. This virus Family includes three other Genera that affect mainly insects, though one Genus also affects amphibians. Because the causative organism is a virus, treatment is beyond the remit of the average aquarist, and indeed is probably beyond the remit of all but exceptionally well-equipped lab researchers with access to state-of-the-art antivirals. Even then, those antivirals may be fairly specific in their action, and may not affect Lymphocystis because the research in this area is still somewhat in its infancy. This link will take you to a research paper on the subject:

http://www.vet.uga.edu/vpp/clerk/Kurkjian/

The virus itself causes growths to appear upon a fish, usually located upon the fins and the parts of the body where the fins originate from, and these growths, in their earliest stages, can confusingly resemble Ich. However, as the disease progresses, the growths become much larger than the typical Ich 'salt grain' dots, and acquire a characteristic appearance resembling lumps of cauliflower growing out of the fish.

I have already said that the disease cannot be cured. However, the disease usually runs a course that ends in the viruses being conquered by the fish's immune system, and the disease coming to a non-fatal end. However, the growths, when they finally recede, can leave behind unsightly scars upon a fish, which are particularly unwelcome in fishes such as show Bettas and other highly pigmented fishes upon which the scars will be conspicuous. For this reason, Lymphocystis is unwelcome in any aquarium, even if it does not kill the fishes itself.

Back in 1977, Tropical Fish Hobbyist magazine carried an article entitled Lymphocystis Disease In The Green Terror, complete with numerous illustrations of the affected fish and photomicrographs of the affected tissues. The course of the disease was plotted, and in order to do this, the author, Dr Harry W. Huizinga, inoculated a second, healthy Green Terror with material obtained from the growths on the first infected fish, so that a definite time-frame for the disease could be established.

It took 20 days after initial infection for the first pinhead-sized Lymphocystis cysts to appear at the site of inoculation. These cysts then grew in size over the next 14 days, until by day 35, they were 1cm across. After day 40, the growths began to recede, until day 60 after inoculation, when they vanished entirely.

Consequently, this disease has a fairly long gestation period in affected fishes, and may not show up in quarantine within a 14 day period. If fishes known to be susceptible to this disease (the link above lists various Families known to be susceptible) are to be quarantied with Lymphocystis in mind, then the quarantine period should be extended to 28 days. One author of a book on marine fishes, Graham F. Cox, cited in his writings in the 1970s that he had experienced a problem with Caribbean fishes introduced into an aquarium that either contained, or had previously contained, otherwise healthy Indo-Pacific fishes: the Caribbean fishes developed Lymphocystis. He speculated at that time that the disease was absent from the Caribbean, but it is now known that the viruses are present worldwide in both freshwater and marine environments. It is therefore more likely that Cox's choice of Caribbean fishes, which tended to include species such as Queen Angelfishes, Holacanthus ciliaris, which are known to be fairly delicate aquarium specimens, was a contributory factor to his experiences.

Miceroscopic examination of the affected tissues reveals something quite remarkable. Those cells affected by the Lymphocystis virus stop reproducing, and instead undergo an amazing degree of enlargement (hypertrophy). Cells thus affected (which tend to be dermal fibroblasts) undergo an enlargement of 300 times normal size, which is, as the TFH article stated, a fairly spectacular enlargement for any cell to undergo. Indeed, the cells enlarge to such an extent that they become naked-eye visible among the 'cauliflower growths' upon the fish! In addition, the outer cell walls of the affected cells thicken, and under the microscope show in addition virus inclusions. These phenomena can be seen under low magnification under the microscope, especially in stained preparations, but to see the viruses themselves (which have a hexagonal symmetry), one needs access to an electron microscope, which at a 20,000 times magnification in transmission mode, reveals the virus particles.

Infection of other fishes is by direct contact. Aggressive combative behaviour between fishes (as is likely in the case of the Green Terrors featured in the TFH article) and fishes eating infected material all contribute to the spread of the virus. Thus, affected fishes should always be isolated wherever possible, and kept isolated until a mimimum of 28 days after the disappearance of the last lesions, because the viruses are fairly persistent. Thus, from diagnosis to final reintroduction into the main aquarium can take over three months' worth of quarantining time. Consequently, this is not only a highly inconvenient disease for the fish, but the aquarist. Normal sterilisation procedures may fail to eliminate the virus from an aquarium, as the viruses may be resistant to some of the disinfecting agents used for sterilising aquaria, an additional complication that makes those aquarists who have never encountered Lymphocystis very glad that their fishes have remained untouched by the disease!

One problem that may arise is that an affected fish may, as a result of developing Lymphocystis, become suscpetible to other opportunisitic diseases during the quarantine phase. The only course of action available is to treat these othe diseases as and when they arise, and allow the Lymphocystis infection to run its natural course.

Although this disease tends to be rarely seen in freshwater aquarium fishse, marine aquarists sometimes encounter it. Among marine fishes, the disease is known to be particularly rampant among Angelfishes if it arises in an aquarium, and often targets an aquarist's most priszd and expensive specimens. Among freshwater fishes, advanced fishes such as Cichlids seem to be the preferred viral hosts.

The website linked to above gives extensive medical information about the disease, including a section on 'differential diagnoses' allowing the aquarist to determine whether or not the disease seen in his fishes is genuinely Lymphocystis, or whether it is one of the other diseases that in the early stages have similar appearance, such as Ich. Recommended reading for anyone likely to encounter Lymphoscystis, particularly those dealing with fishes in the wholesale and retail trades!

And with that, I shall leave everyone to digest my latest offering ...




Panda Catfish fan and keeper/breeder since Christmas 2002

great article as usual, thanks cali /:'