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DISCUS PLAGUE
Posted by: iamlost2 on Thursday, July 25, 2002 - 10:41 AM
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by Kenneth Reeves, DVM
Colorado Aquarium Society
North American Discus Society
In September 1986, a new serious infection of certain cichlid species began appearing in wholesaler tanks all across the United States. This disease, which appeared to have come in with Southeast Asian fish, produced bizarre and devastating symptoms in discus, angels, uarus, severums and oscars. The initial losses were very high, producing intense anxiety among importers and initially panicky responses and ill-advised treatments, which further complicated the problem. When infected fish were imported, the disease spread within days to all tanks containing the sensitive species, suggesting a possible airborne infection. Within a short time, numerous pet stores and fish breeders who handled these species were also experiencing severe disease problems.
When it became apparent the disease was contagious, fish were sent to pathology labs and diagnoses began to be established. Fish with similar symptoms were found to have Hexamitiases, Pseudomonas, Streptococcus, Chondrococcus columnares and Aeromonas. In Europe, the disease appeared at about the same time and organic toxins in the water were blamed. In the Orient, the disease was blamed on an "Alkalosis" problem in the water.
Similarly, treatments were found to be diverse: aspirin, cold tablets, acid water, potassium permanganate, trichlofon, tetracyclines, gentomycin, nitrofurazone, and metronadazole were used successfully by some people, while the same treatments were equally unsuccessful for other people.
During this time of widely diverse suggestions, the second North American Discus Society meeting was held in Orlando, Florida. This meeting brought together a large number of people who had experienced the disease at some level. Roundtable discussions and review of what was known led to a suggestion that an underlying disease must be present, because such mixed etiologies should not result in such similar symptoms. The underlying disease appared to sensitize the fish to other infections and an immune suppression virus was suggested. A committee was formed to encourage collection of still more information on Discus AIDS, or the Discus Plague. Out of this committee came some history and suggestions that will be given in this article to help you deal with the plague.
A typical disease history begins with the acquisition of new fish, plants, decorations or live food, from an infected source. Often the infection is not a sick fish, but a healthy fish or plant from a tank which has harbored the disease in the past. Within 3 to 5 days of exposure, some fish begin to turn dark and seek shelter in secluded corners of the tank. Soon all involved fish are "huddled" in a dark corner, exhibiting extreme shyness, heavy mucous production on the skin, severe "fin rot" and rapid respiration. On closer examination, the fins will show clearn non-pigmented areas where the tissue appears to be dissolved and the mucous layer will be streaky where the fish has been rubbing against objects in the tank. While the fish appear to be very sick, they continue to eat sparingly, moving in a tight school to the food, then swimming as one unit back to a dark corner. Some fish will lie horizontally on the top or bottom of the tank, trying to hide in the smallest shadow. Mature adult fish appear to suffer the most severe symptoms, often dying within the first few days of the disease.
Angelfish have a slightly delayed disease onset, beginning to get sick in 7 to 14 days, and much more severe fin rot is noted. Gold strains of angels seem to be sensitive to swim bladder problems and often struggle helplessly at the surface of the tank. Some people report angel losses to be much higher than discuss losses, but since the fish cost less, they may not be receiving the same intense course of treatment.
After the disease course has ben completed, which takes 7 to 21 days, the surviving fish are very thin, with extremely dense white mucous patches on the skin and often, large defects on the fins where tissue necrosis has occurred. Although recovery of condition after the disease can be spectacular, it is also a time that disease problems with capillaria, gill flukes or hexamitiases may occur and require further treatment.
Surviving fish appear to be contagious for several months afterwards, and can infect a new system while exhibiting no symptoms themselves. Similarly, some systems have been apparently disease-free for six months and new non-immune fish introduced to the system will rapidly become ill while the original inhabitants remain completely healthy.
It is rapidly approaching the point where any discussion of keeping your fish room disease-free is pointless, but here are some suggestions: Any object or organism from an infected source can bring in the disease. This includes used fish bags or styrofoam boxes used to move fish, a borrowed net or filter, new plants, or fish of uninvolved species, can be mechanical transporters of the disease organism. To prevent the disease it is necesssary to research all information regarding any new fish, including if they have been exposed or sick, and if so, what medications were used in treatment. If you elect to get new fish of the involved species, try to isolate them in a quarantine tank, preferably in a separate room, for 4 to 6 weeks, before moving them to your fish room. If you purchase non-involved species or plants, isolate them for several weeks, then move them - but not the water - from the isolation tank to their new home. Fresh water live foods such as goldfish, tubifex or daphnia can be contaminated, so purchase only from the most careful and clean dealers.
Certain guidelines based on the experiences of many people who have experienced the "plague" in their fish rooms, can help you get through the disease with minimal losses. Since there appear to be so many different organisms responsible for the symptoms of the plague, get a thorough history of what bacteria have been isolated or what treatments have been used successfully on fish you are interested in, then make sure you have access to those same treatmens before you get the new fish. Before introducing new fish, do all the filter cleaning and aquarium maintenance you have been putting off. A heater or airpump failure during the plague could have devastating consequences. Finally, bring in new fish only when you will have the time to do the additional medicating and tank maintenance necessary for successful treatment.
When disease exposure has occurred and fish begin to get sick, the most important rule is DO NOT PANIC. Many fish have been lost because the disease is so ugly and frightening that fish keepers made poor decisions on medications and dosages. As horrible as the disease appears to be, your fish can survive well if medicated and maintained properly.
When symptoms are first noticed, begin treating all tanks containing susceptible species immediately with your selected antibiotic. Antibiotic selection can be based on history of the previously infected fish, culture and sensitivity from your own fish, trying separate antibiotics on each of several tanks to find which is most effective, or the use of a broad spectrum antibiotic in the hope it will be effective. Possible antibiotics to try include Chloramphenicol, Tetracycline, Oxytetracycline or Gentomycin. Effective antibiotics will almost immediately arrest the fin deterioration and reduce mucous production on the skin, but will not affect the dark coloration or huddling behavior. Often concurrent treatment with oxidizing agents like Potassium Permanganate will keep bacterial counts down. Temperatures in the 85-90 F range appear to be of some value. A number of people have suggested maintaining a tank pH of 5.5 to 6.5 to reduce bacterial growth during the disease process.
When treatment has been initiated, monitor the tank for ammonia build-up, as the prolonged treatment with antibiotics may damage the filter ecosystem. Feed small amounts of appetizing foods and make daily small water changes, siphoning off any remaining food material to avoid stressing the fish. At this point, do not make any large water changes. The sick fish are easily frightened, so make sure tank covers are tightly closed or some fish may jump. The fish are very light sensitive and turning off the lights may make them more comfortable. Be careful to remove all living plants if you are going to leave the lights off for a prolonged period. Check the tank frequently for any dead fish or dead plant, or uneaten food which may further stress the fish. In 7-21 days, your fish will reappear at the front of the tank, looking for food. At this point make larger water changes and increaseyour feeding as the fish will regain condition rapidly.
The lack of healthy angelfish and discus in your local pet shop should tell you we still do not understand a lot about this disease. Now, nearly a year after the disease has appeared, many breeders still have only minimal production of young fish. Many pairs have never resumed spawning or are producing largely infertile spawns. Also of concern are recent reports of the return of symptoms in fish which had previously recovered from the disease and were considered immune. After an initial denial of the existence of the disease by the tropical fish industry, the condition is now receiving a lot of scientific investigation.
I would like to thank Peter Thode in Maryland, Joe Gargas in Illinois, John Bergenti and Mark Weiss in New York, Lo Wing Yat in Hong Kong, Harold Beck in Texas, Jerry Lofstead in Florida, and Ron Aklin in Colorado, for their contribution to this article -- and AT&T thanks us for our long-distance contribution to their economy.
A report of any experiences you have with this disease would be greatly appreciated by the North American Discus Society.
Please send to:
North American Discus Society
c/o Dr. Kenneth Reeves
P.O. Box 1832
Arvada, CO 80001
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Reprinted with permission from the Colorado Aquarist, publication of the Colorado Aquarium Society, Summer, 1987.
Note: Published at FishGeeks with express permission from the author. This article can not be copied or reprinted, either physically or electronically without the permission of the author. Copyright 2003.
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