The aquarium is inevitably the habitat of undesirable hosts, such as certain bacteria, viruses, fungi and other parasites, which can sometimes make fish sick.
However, usually goldfish do not get sick because they are protected by their immune system.
It is only under certain circumstances, which should be identified, that pathogens can challenge or even overcome the fish’s immune system. Most common causes are stress, poor water quality (inadequate pH, presence of ammonia or nitrite in the water) and poor nutrition. If the fish have been stressed during the juvenile phase (e.g. massive administration of hormones or very high nitrate levels), the fish may develop more health problems later on: buying quality fish from a reputable store is the only solution.
In order to prevent the outbreak of diseases – although this is not always possible – one can take the following precautions:
- Maintaining good quality water suitable for your fish. For goldfish, the pH should be neutral or slightly alkaline. The water should be free of ammonia or nitrite (cheap and easy to use tests are available in good pet shops). Partial water changes should be made on a regular basis. Click here to learn more about aquarium filtration.
- Providing a good diet, in quality and quantity. Do not overfeed. Check regularly that all fish are feeding normally: if not, identify the cause of the problem. Click here to learn more about goldfish feeding.
- Buying your fish from a reputable store is essential. This reduces the risk of introducing diseased fish that could infect others, but also the risk of congenital weakness or genetic abnormality. However, some fish that are carriers of a large number of pathogens may not show clear symptoms (or can even be healthy carriers). Also, if you introduce them directly into your aquarium, they may infect other residents (the weakest ones first). Therefore, quarantining your fish for 10 to 15 days after purchase is a safeguard used by many aquarists.
- Avoid installing the aquarium near an excessive source of noise or close to constant passages. Do not tap the glass unnecessarily. Click here to learn more about installing the aquarium.
- Avoid associating slim-bodied breeds with slower egg-shaped fancy goldfish (unequal access to food): see types of goldfish.
Important: the comments area below is not for urgent queries about fish health but for general feedback, comments and questions, as we normally check comments twice a week. Therefore, it you have a question about a sick fish, it is advisable to first check the health and disease section. If you do not find the answer to your questions there, please post your question in a fishkeeping forum, which usually allows to get help in a timely manner, or contact your local vet.