Viruses are something that DOES happen in aquarium fish, goldfish and Koi collections. The viruses they get are very hard to manage because we don’t have “cures” for them.
VIDEO: What Makes You Think It’s A Virus? What can you do about it?
There has been a virus in Angelfish for years, but we don’t see it much any more. There is a virus infecting guppies and it’s making it hard to keep certain groups of guppies alive, if they all come from the same source in Vietnam or Singapore.
Symptoms include isolating-themselves. Not eating. Mouth deformity. Fin deterioration. Death. Once you see the particular specimen of guppy “off by itself” it’s a short-story of less than 72 hours. They go from “looking pretty good” to dead in less than 3 days. It is USUALLY one or two fish in a group, dying a few at a time while everyone else looks “decent”.
There are a couple viruses of Koi: Spring Viremia of Carp is one, and Koi Herpes Virus is another one. The first virus (SVC) causes weakness and vulnerability to secondary bacterial infections. It doesn’t seem to be a “killer” except that it makes the fish highly vulnerable to Aeromonas and Pseudomonas bacterial infections. So you would see fish breaking out with ulcer disease. The problem with that virus is that getting your fish tested is challenging and if they have the SVC they may have to be destroyed.
In recent months, Koi Herpes Virus has emerged as a fish killer, and which has contaminated the ‘supply chain of Koi into the hobby, both from Japanese fish, Israeli fish and some domestic stocks. There is a treatment. It is not regarded as desirable. A large percentage of hobbyists and pundits would see you kill your fish during and after an outbreak because they don’t want your fish to infect their fish later.
The assumption (and it’s a big one) is that Koi Herpes Virus is carried by asymptomatic carrier fish at all temperatures and circumstances while we know factually that the carrier state, and recovery, are actually temperature-dependent, AND NOT stress related.
Our only “assertion” is that residential non-commercial hobbyists should be aware that there is a successful treatment by increasing the water temperature to 84dF and holding it there consistently for 72 hours. Of course other conditions and circumstances exist. Read up on this virus via these resources. (Link)