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Common Fish Diseases Your Fish Might Get






It hurts so much if our when our lovely fishes in the tank fall ill. As they say, “prevention is better than cure”, we always wish we had enough information in order to avoid or prevent it. Here is a list of most common fish diseases in freshwater aquariums.




Grayish white marks or patches on the body of the fish or around it mouth are the first signs of Columnaris. They appear like threads, majorly in the vicinity of the mouth. The fins may show deterioration, the gills get affected and slowly sores start appearing on the body. This disease is caused by bacteria and mostly a direct result of poor water quality. The shock of being introduced to the new aquarium leads to Columnaris in newly imported fish, occasionally. Anti-bacterial medications can solve it if the diseases is discovered and treated in early stages.

Gill Disease:

Gill disease makes the fish appear to be swimming in a great hurry, but does not move at all. The fins flap very fast, and fish gasp for breathe at the surface, or lie listless at the bottom. Gills become swollen and discolored. Bacteria, fungi and parasites cause this. First step involves improvement of water quality. Frequent water changes, conditioning and dechlorinating the water is required to prevent gill disease. Adding anti-bacterial solution to the water will cure the fish.


This disease causes small, grain-like spots on their body. It is also known as white-spot disease. The fish tries to sctratch the itch against the décor or hard surfaces in the aquarium. This is very contagious and caused by a protozoa called Ichthyophthirius Multifilis. It is very difficult to control if not detected in early stages. Adding salt to the water is an effective way to treat the whole water of the tank. Medications based on Malachite green and formalin control this parasite but Malachite green is harmful for scaleless fish.


The common symptom is a hallow or swollen abdomen. Fish’s scales may stand out in these areas. Fish appear listless and lose appetite. Viruses and bacteria cause dropsy. Bad water or infected food cause dropsy outbreaks. The condition becomes incurable if the damage reaches the kidney. It is less infectious. Commercial remedies cure this disease best.


Fin-rot causes fins to turn opaque and become blood-streaked. The erosion reaches the base of the fin and then, the fish dies. Disease appears only when the fish is stressed, or when the fins have already been damaged. Anti-bacterial medicines are to be used to treat this.

Fungal infections:

The fungus spores can cause infections when the fish already has damaged gills or skin. They are typical secondary infections. White, cottony growth appears on the body of the fish. Anti-fungal medicines fight the infection.

Hole in the head:

Fish develops small pits in the head region. Holes are usually white in color and trail yellowish mucus. Fish become listless, lose color and stop feeding. This is caused by protozoa and is a secondary infection. Poor water quality and poor diet leads to this infection. Fish should be isolated in a quarantine aquarium and then treated. Direct injections or medicated food can cure this disease.


Fish’s eye starts enlarging in this case. The causes could be bacteria or too much dissolved oxygen. Isolating the fish and anti-bacterial medications is the treatment.

Swim bladder disease:

It affects the fish with globoid body shape. Fish loses buoyancy. The fish remains at the bottom, unable to rise or float. Any damage to the swim bladder membrane causes this disease.

Fish Lice:

Small, white lice appear on the body and fish start rubbing against hard surfaces. Red spots or sores develop. The best way is to remove lice using a tweezer. Siphon the substrate daily to get rid of eggs.

Nematode worms:

The anus of the fish protrudes a little and a thin thread like worm drifts out of the anus. Fish becomes listless, bloated and refuses to feed. Anti-worm medications are effective against these worms.