Rainbowfish diseases
Rainbowfish diseases

Rainbowfish diseases

Just like any other fish, the rainbow fish can suffer from various health problems and diseases. They are however remarkably sturdy and disease is rarely a problem in well-kept rainbowfish aquariums. Even a skilled and dedicated aquarist can however be forced to deal with diseases in his or her aquarium, since disease sometimes occur even in “perfect” aquariums. It is therefore a good idea to do some reading about common fish disease in advance; that way you will know what to look out for and can spot signs of disease at an early stage. You can read more about common fish diseases on our fish disease page.

A good thing about rainbow fish is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed.

Preventing disease

The best way of preventing disease is to keep your rainbowfish in a suitable environment and provide them with a varied and nutritious diet. The more accurately you can resemble the natural environment of your particular species when it comes to temperature, pH-value, water hardness etc, the stronger and more capable of combating disease your fish will become. You should also keep rainbowfish in large enough groups and provide them with a big enough aquarium that is well decorated and has plenty of hiding spots. Failure to do so will result in stressed fish that easily succumbs to disease. Last but not least, keep an eye on the levels of ammonium, nitrate and nitrite in your aquarium. These compounds (collectively known as organic waste products) will weaken your fish and make them more susceptible to illness. Well functioning biological filtration and frequent water changes are necessary if you want to keep these levels down. Water changes are always necessary in an aquarium, since we keep adding new organic compounds to it every time we feed our fish.

Everything you add to the aquarium might bring disease. Fish are not the only ones that can harbour malicious organisms; other animals, plants, gravel and even aquarium decorations and equipment can also be carriers. Animals should therefore always be quarantined, while plants and dead things should be cleaned. You can read more about cleaning and guaranteeing in the category about disease, see link above.

Acting early

When you notice signs of disease, you should ideally set up a quarantine aquarium at once and move all fish with symptoms to that aquarium. It doesn’t have to be a large or fancy equipped aquarium; a simple container with an airstone is often enough. A filter is good, but if you have no extra filter you can make up for it by carrying out small and frequent water changes. Don’t shock your sick fish by placing it in a quarantine aquarium where water temperature and chemistry differs a lot from its normal aquarium.

If it is impossible for you to set up a quarantine aquarium, you might want to think about euthanizing your sick fish, at least if you suspect a dangerous disease that is hard to treat. Euthanizing a few fishes is often better than allowing them to spread the disease to all the inhabitants in the aquarium. You can euthanize a rainbow fish by scoping it up into a plastic container together with plenty of aquarium water and place the container in the freezer. The water temperature will gradually decrease, and since the rainbow fish is a cold blooded animal (unlike mammals) it will gradually decrease its own body temperature until it falls into a state of hibernation and finally dies in its sleep.


The proper treatment will of course depend on the disease and it is therefore impossible to provide any general guidelines about how to treat disease in the rainbowfish aquarium. Two of the most commonly encountered diseases in rainbowfish aquariums are White Spot Disease (also known as Ich since it is caused by the parasite Ichthyophthirius multifilis) and Velvet (which is caused by a parasite called Oodinium). Just as the names suggests, White Spot Disease causes white spots to form on the body of the fish, while Velvet gives the fish skin a velvety look. There are however a long row of other diseases capable of infesting a rainbowfish aquarium in addition to these two common ones. You can read more about different fish diseases and their symptoms and treatments in the category mentioned above.

Keep in mind that most treatments are tough for your rainbowfish; sometimes almost as tough as the disease itself. Neglecting an aquarium and then using various medicines to combat all the problems that arise as a result of the neglect it therefore not a viable solution in the long run. Fish that are kept in an improper environment are often too weak to survive the treatment.

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