Mastering Freshwater Aquarium Ecosystems
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Fish Health (Cont.)

The discus plague is highly contagious but appears to be only transmitted between discus. Unfortunately, any discus exposed to this virus should probably be destroyed to prevent the transmission to other fish. The disease still has a lot of study yet to be done on fish that have been infected, and how long they may shed the virus. It is currently unknown if the fish will always shed the virus or if the fishes natural antibodies will eventually eradicate the virus. It is known that discus will shed the discus plague virus for more than six months. Also unknown is, if a system has been exposed to the discus plague virus, and all fish have been removed, how long can the virus survive without a host.

You should never purchase a fish from a facility that has fish that exhibit symptoms of the discus plague virus in any of their tanks. The virus can be transmitted through water cross contamination, so any water in a facility that contains fish with the discus plague virus can potentially introduce the virus to your systems even without the fish.

There is currently no cure for the discus plague virus. The virus might respond to heat therapy, by increasing the temperature to 90º F (32º C) as there are other viruses in the same family that have responded to heat. The tank must have good water circulation when using heat therapy as water will have a lower oxygen carrying capacity. Having antibiotics on hand to treat any secondary infections is a good idea, as bacterial infections often occur in discus when a heavy slim coat appears.

Angelfish Virus

Angelfish also have a related virus that causes the same symptoms as the discus plague virus. The angelfish virus should be treated in the same way as the discus plague virus.

Koi Herpesvirus

Koi herpesvirus (KHV, cyprinid herpesvirus-3 or CyHV3) was first discovered in England in 1996. KHV is highly contagious, commonly causing mortality in greater than 95% of koi and common carp (Cyprinus carpio) it infects. Infected koi are reported to die within 24 to 48 hours after first symptoms are observed. Most obvious symptoms are swimming lethargically and staying near the surface. The easiest way to detect a possible KHV infection is to check the gills for dead white patches (normal is red), and in some cases sunken eyes.

Koi with classic KHV symptoms

Koi with classic symptoms of a KHV infection. Notice the white patches on the gills and the sunken eye. Photo by Dr. Thomas B. Waltzek.

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