03-11-2013, 03:05 PM
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Unfortunately this disease is not always detectable externally. Fish infected may show no external signs whatsoever, yet they can pass the virus to one or more fish in the same water--and this is now known to spread to other species than gourami--without ever contracting it themselves. Only biomedical tests can determine if the fish is or isn't infected, and that is beyond most of us.
The "dealer" issue refers to the actually breeder of the fish, not the store. It is where the fish come from. A hobbyist starting out with wild stock or known safe tank-raised fish and breeding his own and selling them is safe. Some stores carry such fish, some don't.
Stores that get their fish wholesale from unknown sources are the most risky.
You can read more on this disease in this excerpt from an article by Neale Monks; I can't provide the link because the site has a forum and we don't allow links to other forums. Sparkz, I see you are in the UK; Dr. Monks happens to live in England, and is extremely knowledgeable and helpful.
Fish viral diseases are impossible to treat directly; the best you can do is avoid buying infected fish and quarantine all new fish prior to putting them in your fish pond or aquarium.
Identification and Transmission
Although fish with viral diseases may display symptoms the aquarist can recognize, positive identification requires biomedical tests beyond the abilities of the average fish hobbyist.
Viruses can be transmitted between fish by direct contact, or by water or wet objects being moved from one fish aquarium to another. In situations where the virus is known to be extremely contagious, as with the koi herpes virus (KHV) and dwarf gourami iridovirus (DGIV), strict quarantining procedures are essential.
Dwarf Gourami Iridovirus (DGIV)
The quality of the dwarf gouramis in the trade has steadily declined for years, with batches of fish showing significantly higher levels of mortality than 10 years ago. Historically, retailers and aquarists have blamed bacterial infections, such as fish tuberculosis (Mycobacterium marinum). In recent years, though, attention has focused on a virus known as dwarf gourami iridovirus or DGIV.
Dwarf gourami iridovirus is apparently specific to the dwarf gourami (Colisa lalia), including the various fancy varieties of the species, such as neon gouramis and sunset gouramis. Infected fish develop a variety of symptoms, including loss of color, decrease in activity and appetite, the appearance of sores and lesions on the body, abdominal swelling and finally death. This fish disease is highly contagious, completely untreatable and invariably fatal.
Dwarf gourami iridovirus is apparently very common. One recent study of fish exported from Singapore found that 22 percent of all dwarf gouramis carried the virus. Aquarists should never purchase dwarf gouramis from fish aquariums containing fish exhibiting symptoms consistent with the dwarf gourami iridovirus, and all new fish should be quarantined for at least six weeks prior to being placed in the main fish aquarium.
For most aquarists, my best advice is to keep the hardier alternatives to dwarf gouramis. The thick-lipped gourami (Colisa labiosa) and the banded gourami (Colisa fasciatus) are both similar in size, temperament and coloration and make excellent alternatives.