Poor water quality, aggressive tank mates and injuries can all lead to stress in gouramis, and stressed fish have an increased susceptibility to disease. If your gourami falls ill, your first course of action should be to prevent the disease from spreading to other fish in your tank. Once you have isolated the sick gourami, you can then take steps to identify and treat the disease. The sooner you take action, the higher the chances are that your gourami will recover successfully.
Before you even attempt to identify the disease that your gourami has contracted, quarantine the sick fish. By removing the sick gourami from the tank you can reduce the chances that the disease will spread to other fish and it will also make treatment easier. A gourami quarantine tank should be about 20 gallons in capacity and it should have a bare bottom to make cleaning easier. Equip the tank with a submersible aquarium heater and a sponge filter. Sponge filters are better than standard power filters for quarantine tanks because the suction and water flow they create is not so strong as to disturb sick and injured fish.
Once you have settled your sick gourami in the quarantine tank, you can begin to observe his symptoms in order to determine what type of disease he has. Examine the skin, fins and gills of your fish -- if the gourami exhibits white, cottony growths, he likely has a fungal infection. Abnormal or erratic behaviors such as rubbing against tank objects are often a sign of parasite infections, though some parasite infections are internal and difficult to diagnose. Bacterial infections typically affect the outside of the body and may present symptoms such as loss of appetite, weight loss, ulceration or streaking on the skin and rotting or fraying in the fins. Viral infections are among the most difficult diseases to diagnose. If your gourami's eyes darken or begin to bulge, or if the fish shows signs of bleeding around the gills or eyes, he may have a viral infection.
Identify the Disease
After compiling a list of your gourami's symptoms, you can begin to identify the disease. If possible, use the list of symptoms to narrow down the type of disease: fungal, parasite, bacterial or viral. Once you have this information, identifying the disease can be as easy as performing an online search. Perform a search for the type of disease you suspect is affecting your gourami and peruse the list of common diseases that fall under that category. Compare your gourami's symptoms with those on the list in order to determine the specific disease.
Treating the Disease
After you have identified the disease you can begin a treatment regimen. While researching the disease affecting your gourami, check to see if there are any specific treatments recommended for that particular disease. Salt baths are often recommended for external parasite and bacterial infections, though chemical medications such as formalin, potassium permanganate and malachite green are also popular. For fungal infections, anti-fungal agents like phenoxyethanol and malachite green can be effective. Many viral diseases have no known cure and, in many cases, the disease is fatal.
If you have chosen to utilize a power filter in your quarantine tank instead of a sponge filter, then you may need to remove the filter media before you begin treatment. Filter media like activated carbon will remove any chemical medications from the water, thus making them ineffective. While treating your sick gourami, it is essential that you maintain regular water changes using a gravel vacuum to remove solid waste from the bottom of the tank. Make sure the water you use to refill the tank is the same temperature as the water in the quarantine tank to avoid shocking your sick gourami with a sudden temperature change.