Helping you keep your aquarium beautiful and healthy

Diseases of Aquarium Fish: Symptoms and Treatment

If you are an aquarium hobbyist, you know there are many factors that contribute to a healthy and beautiful fish tank. Whether you collect tropical fish and sea life or freshwater creatures, you know this hobby involves more than just keeping fish. In order to maintain an optimal aquarium environment, you need to know how to recognize the signs of disease. Being familiar with typical diseases of aquarium fish and their treatment is an important part of the aquarium hobby. The guide below will help you get started.

Fungal Diseases

Fungal spores are always present in aquariums. An outbreak of fungal disease happens when a fish scrapes or damages its scales or gills. The main symptom of fungal disease in aquarium fish is the development of white, brown or gray cotton-like growths on their skin, gills or fins. Salt baths and antifungal tank treatments are the most common ways to deal with fungal diseases.

Bacterial Diseases

Bacteria are transmitted from diseased fish to healthy ones through the gills or skin. When bacteria enter the fish's body, it becomes bacterial disease. When bacteria stay on the surface of the fish's body, it can develop into a bacterial infection. Both bacterial disease and bacterial infection are very common. The most common forms of bacterial disease are finrot, tailrot, flex and septicemia. The best treatment for these problems is prevention. Providing good water conditions is the best defense. Maracyn and Maracyn 2 are common treatments for bacterial problems in aquarium fish.


Dropsy is a bacterial infection of the kidneys that causes the fish to bloat, often leading to protruding scales. This is contagious, and tends to attach weak or sick fish. If you notice this problem, mix one percent of antibiotic with the fish's food. Make sure the fish are not overfed, because they will need to eat all of the food in order for the treatment to work. You can also buy antibiotic drops at your local pet store.

Viral Diseases

Another common disease of aquarium fish is the viral disease. This disease is difficult to identify in fish until it has already progressed. This is because they begin with tiny cells that are too small to see. Later stages will make the fish look darker, cause the eyes to bulge out and show traces of bleeding. The bleeding associated with viral diseases will often make aquarium fish oxygen-deprived. There aren't really very many treatment options for viral diseases in fish yet. Aquarium fish can fight the virus off with their own immune system. The best thing to do is provide excellent food and water conditions to assist the fish's system in fighting off the disease.

Protozoan Diseases

There are several different aquarium diseases found within this category. The most common are:

  • Velvet (or "Rust") is characterized by clamped fins, difficulty in breathing and tan or yellow dust on the body.
  • Costia can be recognized by a milky cloudiness on your fish's skin.
  • Hexamita appears as slimy and white feces from your fish.
  • Itch is characterized by salt-like specks all over your fish's body as well as excessive slime, breathing problems, loss of appetite and clamped fins.

There are several different treatment options for aquarium fish suffering from protozoan diseases. Some of the treatment options involve chemicals, others have to do with the fish's diet. If you suspect your fish may have contracted a protozoan disease, talk to an expert at your local aquarium supply for a good recommendation.


Ich is one of the most common sicknesses that affect aquarium fish. It is caused by protozoa that live on the fish's skin. Fish with ich look as though they have tiny white dots all over their bodies. They often scratch against objects in the tank. The best way to treat ich is to use an ich medication you can buy from your pet store. These typically contain malachite green or copper. Keep in mind that the malachite green can stain plastic in the fish tank. Because the protozoa swim freely in the tank, treat the entire tank, not just the fish that look ill.