Preventing Disease

How Do I Keep my Fish From Getting Sick?


While there is no way to guarantee that your aquarium fish will never get sick, there are a few simple precautions you can take to protect them against illness. The easiest way to prevent disease in your tank is to avoid introducing harmful pathogens to the tank in the first place. Pathogens can be introduced into the tank through a variety of means but the most common way is through infected fish. In addition to preventing disease from entering your tank, there are a few things you can do to keep your tank environment healthy for aquarium fish. Fish that are content with their environment are less susceptible to disease.

Fish Disease Prevention

Preventing an outbreak of disease in your tank starts with making sure that the fish you bring home are healthy. If you make a trip to your local pet store and end up bringing home a fish that is a carrier for disease, it may not be long before your entire tank is infected. It is not always easy to tell by looking at a fish whether it is sick or not so there are a few precautions you should take to avoid introducing sick fish into your tank. When you get to the pet store take a quick look around – examine the tanks to see whether they are clean and whether there are a large number of dead fish floating around. If the tanks do not appear to be well-maintained or if the fish in the tanks look ill, do not purchase from that store. Observe the fish themselves and pick out specimens that display healthy coloration and activity levels because these fish are less likely to be carriers of disease.

Once you have brought your fish home it is essential that you keep them in quarantine for a minimum of two weeks. Even if you think the fish you purchased are healthy, they may still be carrying a disease that could infect your other tank inhabitants. A quarantine tank is simply an extra tank set up to mimic the conditions in your main tank. This tank does not need to be as large as your main tank – a 15- or 20-gallon quarantine tank is perfectly sufficient for most aquarium fish. Make sure the tank is equipped with a proper filtration and heating system and try to maintain the temperature and water parameters so they match those in the main tank. Keep your new fish in the quarantine tank for at least two weeks, observing them for signs of illness during that time. If, after the two weeks is up, the fish still appear to be healthy you can safely add them to your main tank.

Other Prevention Tips

In many cases, aquarium fish diseases are brought on by stress. When a fish becomes stressed, its immune system weakens and it becomes more susceptible to the diseases and pathogens to which it may become exposed. This is to say that an otherwise healthy fish is less likely to become infected when exposed to a pathogenic virus or bacteria than a fish that is already suffering from stress. Several factors may contribute to the level of stress your fish experience and, as the aquarium hobbyist, you have some degree of control over all of these factors. The most common stress inducer in aquarium fish is poor water quality. If the water chemistry in your tank is unstable or the tank itself becomes too dirty, your fish could suffer.


To keep the water quality in your tank high, be sure to perform water changes on a weekly basis. It is also wise to test your aquarium water once a week to keep an eye on the water chemistry levels. If you regularly test your aquarium water you are more likely to spot a problem sooner and will be able to correct it before it affects your fish. Bullying by aggressive tank mates can also cause fish to become stressed, especially when the bullying results in injury. In order to mitigate a bullying situation, consider removing the aggressive fish to another tank. In some cases, providing extra hiding places may also be enough to relieve the stress of bullied aquarium fish. Taking these simple precautions against stress in your tank can make a big difference in the health of your fish. If you are serious about preventing outbreaks of disease, do everything you can to ensure that your fish are given a healthy, stress-free environment in which to live.

What are the Most Common Fish Diseases and How Do I Identify Them?

While keeping your tank clean and feeding your fish a healthy diet are essential if you hope to prevent your fish from falling ill, these precautions do not guarantee that your fish will never get sick. If your fish become stressed or are exposed to a disease, they may fall ill despite all your hard work to prevent it. Aquarium fish diseases can be divided into four categories: bacterial, fungal, viral and parasitic. In order to properly treat your fish when they fall ill, you should be able to identify the type of disease your fish has. It is not practical to memorize the symptoms of every fish disease out there, but you can learn the basics about the most common types of fish diseases to be better prepared.

Types of Fish Diseases

The most common type of fish disease you are likely to see in your tank is a bacterial infection. These diseases are especially common in tanks where the water quality is low and the immune systems of fish are already weakened due to stress or injury. Some of the most common bacterial infections include fin rot, mouth fungus, dropsy and red pest. While the symptoms of each disease may vary, common symptoms of bacterial infections include lethargy, anorexia, inflammation, rotting fins and ulcers. Systemic, or internal, bacterial infections may also cause haemorrhaging and the build-up of bodily fluids. If your fish display some of these symptoms, do a quick web search to determine which bacterial disease they are infected with and follow the recommended treatment protocol.

Fungal infections are also fairly common in freshwater aquariums because most tanks already have fungal spores present. When the water quality declines or fish become weakened due to stress or injury, these spores spring into action and spread quickly through the tank. In addition to being fairly common, fungal infections are also fairly easy to diagnose. Most fungal infections involve the development of fluffy white or gray growths on the mouth, gills and body of fish. While external fungal infections are most common, systemic infections do occur and they can be very difficult to identify and to treat. In addition to visible growths, fish with fungal infections may also exhibit a loss of appetite and difficulty breathing. Treatments for fungal infections usually involve salt baths or the administration of some kind of antifungal agent. To find the best treatment for your fish, do some basic research to identify the particular disease.

The third type of fish disease is parasitic infection and because these infections can spread rapidly through the aquarium, many hobbyists prefer to treat their entire tank rather than individual fishes. As is true of the other three types of freshwater fish disease, parasite infections are more common in tanks where the water quality is low and the fish are already stressed. The most common symptom of parasite disease involves the fish rubbing itself against objects in the tank. Some parasite diseases, such as Ich, may produce tiny white growths on the fins, gills and bodies of infected fish. Other common symptoms of this type of disease include rapid breathing, clamped fins and increased mucus secretion. Though the ideal treatment varies from one disease to the next, common treatments for parasite diseases include medications such as formalin, potassium permanganate and malachite green.


The final type of freshwater fish disease is viral infection. This type of infection can be very severe and it is the most difficult type to treat and to diagnose. Viral infections often manifest in the form of wax-like growths on the bodies of fish and other common symptoms include bloating, haemorrhaging, bulging eyes and reddening of the skin. Because many viral infections produce symptoms that are similar to other types of fish disease, many aquarium hobbyists do not realise their fish have a viral infection until it is too late. Most viral diseases have no cure and even if the fish survives, it may be a carrier for the disease the rest of its life. Some of the more common viral diseases include fish pox, Lymphocystis, viral haemorrhagic septicaemia and, in dwarf gouramis, Dwarf Gourami Iridovirus.