The most obvious way to determine a sick fish is to view it’s body for any unusual spots or growths. Ich is a common illness characterized by white spots around the gills or on the body. Ich is a species of ciliate protozoa that is often introduced by snails, new fish or caused by changes in the water condition. Should you notice these distinctive white spots you can treat the tank by adding chemicals that will kill the ciliate protozoa. You can also quarantine fish that may be infected until they are healthy.
Another way to determine that your fish may be sick is to notice it’s changed behavior. A common symptom of illness is flashing. Flashing is when the fish appears to be scratching itself on the substrate or rocks and wood in the tank. Flashing could be a sign that the fish is developing an infection on the body.
The fish may also be swimming erratically. This might include darting around the fish tank, moving up to the surface or spinning round on itself in a constant motion. This erratic behavior indicates that the fish is stressed in some way. This may be because the water condition has changed or that the fish is suffering from some kind of illness. As many conditions that affect fish can be attributed to poor water quality it is important to check the water condition first. This could solve the problem immediately and in the future.
Another behavior that might indicate a problem is that the fish are staying around the filter or on the surface a lot. This indicates that they are trying to get more oxygenated water and again might be due to the water quality or may be an illness.
Once you have attained as much physical and behavioral data as possible about the fish you could then consult a fish disease book or visit a website on fish disease. These media often have diagnostic questionnaires on the condition and behavior of the fish. They will ask questions about the fish and help you to determine the problem with the fish and the appropriate action to take.
As a last resort you could take a skin scrape or biopsy of the fish and have the sample diagnosed by a professional. Of course this could create more stress for the fish that could make the condition worse and it is quite costly.
Water condition is the most important factor to consider when keeping your fish healthy. Diligent care of the water and habitat will ensure that your fish don’t suffer from any of the common illnesses. If they do however you can follow the advice listed and take the appropriate action.