How To Identify and Treat Freshwater Fish Diseases

Treat the Most Common Freshwater Fish Diseases, Making Your Fish Healthy and Beautiful

In this article you will find some of the main information about how to identify, treat and prevent the most common diseases and health problems in freshwater fish. Maintaining a good water quality with water changes, not overfeeding fish, maintaining an adequate amount of fish for the available space you have, choosing species with similar behavior, and controlling the levels of PH are all good tips for you to have a healthy and beautiful aquarium. But even if you pay attention to all of these recommendations, a disease can strike at any time.

  1. Ammonia or nitrite/nitrate poisoning. These are not diseases, but rather health problems caused by bad water conditions. Ammonia, nitrite and nitrate are toxic substances that can kill your fish. There are ammonia and nitrite/nitrate tests you can buy and use for an easy verification of the levels of these substances.

    If the ammonia level is high, the fish may have red gills, possibly with inflammation. They are usually on the surface, gasping for air. If nitrite and nitrate levels are high, your fish will look lethargic too.

    These high levels are generally caused by a large bio-loud in your filtering system, and many times because of a great population in a small tank. In this case, you had better find another home for some of your fish. Using a new and more powerful cleaning and filtering system will help you. In the aqua stores you can find some products to reduce the levels of ammonia, for example (most part of them are used in the filters, the same way you do with carbon). But anyway, your fish are being poisoned and you need a solution immediately: you need to perform water changes. Renewing about 1/3 of the water volume is recommended, but of course if you already have some experience, you can perform changes for bigger amounts. You can check my article about How To Clean The Water Of Your Aquarium.

  2. Ichthyophthirius -- Ich (whitespot). White spots in the body of your fish, mainly on the fins -- this is the symptom of the most common fish disease for freshwater aquariums. Ich is a parasite that infects your fish very quickly and can be really contagious, so in case of infection you may treat your fish separately and pay attention in the others. The best advice I would give you for preventing Ich infections is maintaining your water temperature above 25ºC or 82ºF, turning the cycle of the parasite faster. Water changes are welcome in this case, too, for maintaining a better water condition. It is important to use the correct medication: it is easy to find remedies for Ichthyophthirius infections, but most of the medications include other parasite species infections.
  3. Fin rot. A really common and not so dangerous disease; the symptoms are, of course, rotting fins and also loss of appetite. The fish stay in the bottom of the tank. It is a bacterial infection usually due to poor water quality. Medication against bacterial infection and a better water quality are necessary (water changes an so on).
  4. Fish fungus. The main symptom is cotton-like growths on the body that may appear white- or gray-colored. It is usually a secondary disease: The fish already have a bacterial or parasitic infection, and because of the poor water quality and many other factors there is a good opportunity for the fungus to develop in the fish. It will be safer to treat the fish separately from the others, because it can be really contagious. Use the recommended medication for fungus.
  5. Hole in the head. Small holes in the body and mainly in the head of the fish indicate a very common disease in fish from the Amazon. The treatment is basically water-changing and giving the fish medication. Feed the fish with vitamin-enriched foods and change out or stop using activated carbon even if you don't use any medication. Some says that activated carbon use can increase the severity of the disease.
  6. Pop-eye. One or both eyes of the fish seem to be sticking out and sometimes, in advanced cases, the fish can get a really shocking look. Usually this is the consequence of bacterial infections, so you may use remedies against this, and also maintain a good water quality.
  7. Oodinium (velvet). The fish have a similar appearance to fish with Ich (whitespot) infections, but in this case the spots are smaller, yellow-gray and dusty. Fast gill movement and rubbing on surfaces in the tank (like rocks and plants) are common reactions from the infected fish. Oodinium is normally brought with new fish and plants from other aquariums, so in most cases the disease is not directly linked to water conditions. Therefore the best way of preventing Oodinium infections is performing a quarantine for the new fish before introducing them in your tank. If you already have an infected fish, use recommended remedies for parasitic infections and diseases.


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Hmm.. I think my piranha may have #5, thanks for the info!

By Stephen Sandecki

Great information! I wish I would have read this while our fish were still alive .... :0)

By Amanda Larson