Beware of the following pond fish viruses that kill fishes

They can be highly infectious in high populations and as the cooler conditions suppress fish immune systems. Parasites may also spread them. There is no known cure for them at present.

Carp pox. Cyprinid Herpes Virus 1: The formal name for CyHV-3, better known under its old common name of Koi Herpes Virus (KHV).

SYMPTOMS: Solid waxy lumps on fins, body and mouth. Also there will be lesions on the gills. It is the present day scourge of fish breeders around the world because breeding tanks it can result in the death of fish on a grand scale. However it has been shown in some studies to be most contagious at ideal water temperatures of around 20C. At temperatures below 10C and above 30C the symptoms abate. In some experiments in Israel have produced immune fish by moving infected fish to cold or warm water for a period of time. There is also a vaccine for it on offer in some countries but not in the UK at the time of writing.

Spring Viraemia of Carp: SYMPTOMS: The first signs of SVC disease is that the infected fish may breathe and move more slowly, perhaps forming groups the edge of the pond or at a waterfall inlet, and or lie on their side at the pond bottom. The skin and gills may appear dark red and the eyes may seem to bulge, the belly may be swollen, and bloody mucus may hang from the anus. Fluid gathers in the stomach cavity and the liver and spleen. Blood gathers in the swim bladder, and there is a reddening and swelling of the gut. Many experts warn that fish showing the external symptoms do not necessarily have SVC and that they are the symptoms as some other diseases like dropsy.

Fish that don't die from SVC may recover and appear healthy, but these fish actually may remain infected with the SVC virus and continue to shed and spread the virus to other fish. Because the SVC virus may remain hidden in infected fish, the disease is difficult to eliminate from a site. In other words there is no cure apart from the complete cull of all fish stock and the disinfecting of all the pond and waterways. Observers have noted that infected fish are more likely to recover if they are kept at water of temperature of around 20C. It is however a modifiable disease and so if you were such a keen fish keeper you showed your fish at popular fish shows, you would not be able to mix your fish with stock from other sources. Contamination can occur from tainted water, equipment or fish louse or leeches.

What makes SVC even more of a problem is that diagnosis of the virus in fish can only be confirmed through virus isolation and other sophisticated diagnostic tests done by an approved laboratories.