The Dwarf Gourami Iridovirus is a fatal virus that commonly affects Dwarf Gourami, and has been shown to be highly related by 99.9% to the iridovirus that affects other anabantid species (ex; Betta, Gourami, Paradise fish). Since it is related to so closely to the other iridovirus, it is thought that they were all from the same origin location in Southern Asia. In the past this virus was noted to be a type of bacterial infection that would cause internal damage that lead to death, however in more recent years this disease has made itself known even to the most safest and healthiest breeders. Due to the odd nature of this virus, even the most healthiest fish can appear to not have Dwarf Gourami Iridovirus until many months or years later when the disease starts to shown itself, making it extremely hard to stop this disease from spreading.
It is extremely hard to tell if a anabantid is infected since the symptoms will not show until months or years through the fish's lifespan. For those fish who are able to carry this disease without it effecting them, it is virtually impossible to know as they will never show any symptoms or signs of infection. Once the disease does start to make itself known on the infected fish, we will see a variety of symptoms which can range from lack of appetite, breathing more heavily through both the mouth and the gills, having a hard time swimming to the surface of the water, coloration fading from the scales of the fish, and most importantly a enlarged spleen which will appear like the fish is extremely bloated.
Since many of the symptoms match those of other disease it can be very hard to rule that this is the disease that is truly taking hold of the fish. Once the disease starts to get progressively worse more symptoms will appear which will rule out any other disease and let you know that this is the iridovirus. These final symptoms will include the fish being unable to swim to the surface of the water (which for any labyrinth fish is a requirement as they need to expand their lungs with air), the coloration may appear to be very dull or dark with some grey areas, the fish will lay at an angle or flat on the bottom of the substrate, other bacterial infections may start to show additional symptoms, and lastly the fish will drown due to them being unable to get air from the surface of the water.
One study by a team led by Professor Richard Whittington of the University of Sydney, Australia found a 99.95% genetic similarity between the Dwarf Gourami Iridovirus and a virus outbreak in 2003 that killed farmed Murray Cod, Maccullochella peelii peelii. A test showed that Murray Cod can be infected with the Dwarf Gourami Iridovirus had upwards of a 90% fatality rate. Unfortunately, there are many statistics elsewhere that state that 22% of Dwarf Gouramis coming out of Singapore have this virus from various breeders. Thankfully, the 22% number is actually the percentage of Dwarf Gouramis in Australian retail aquarium shops that when tested, were found to be infected with this virus. All the tested fish had been imported from Singapore, and thus many have jumped to the conclusion that this sample size must represent the actual number of infected species total from the country.
Since the fish are in contact with each other throughout the breeding and shipping phases, this disease is allowed to spread to most of the population. Even though many stores who sell fish do quarantine any new arrivals, it can be hard to determine which if any fish is infected due to it not showing any symptoms until the fish's immune system becomes weak. Other times even if the new arrivals of Dwarf Gourami are healthy, if there was any traces of a dead or sick fish with this disease it can spread through the water column or if the fish eats any poop that has been leftover from an infected fish. Other theories have been tested that have shown that other species may act as carriers of the virus, but not show any signs of infection. However, since there are many different types of iridoviruses in the aquatic industry, it would require significant levels of effort to test a variety of species to get a sample rate that would show any signs of significance.
Treatment and Medication
Unfortunately, there is no known cure to this virus. Although many have stated that using a bacterial and fungus medication does slow down and can prevent death, there is no known documented reports that such medicines have cured the fish in question. Many have tried to help the infected fish when the disease takes hold by lower the water level in their tank, but due to the fish not being able to eat it will die from starvation. The only way to make sure that you do not get any fish that have this disease is to always buy from a store that is not only reputable, has not had any fish die showing the symptoms listed above, but mainly only gets new fish from trusted and well known breeders who report back of any fatalities within the scope of the fish in question.