Common Freshwater Fish Diseases & Processes to Deal With Them

When it comes to your pet, you will surely want to keep them hale and hearty, along with proper maintenance of their colouration. However, it comes up often that your aquarium fishes are suffering from freshwater diseases. They are at high risk when their disease is not identified at the initial stage, for which their immunity system gets compromised. In “Common Freshwater Fish Diseases & Processes to Deal With Them” You’ll get a brief detail:

 Diseases can occur owing to different reasons, well-known among them are stress, low water quality, improper filtration, overpopulation, irregular diet and continuous fin nipping by other fishes. Any experienced veteran can be well accustomed to the care and treatment of their pets. However, in case you are a newbie, you need to study different freshwater fishes, their symptoms, the intricate processes of their care and their requirements to dwell in the concerned tank that you are keeping them in.

There are innumerable symptoms, illnesses and physical difficulties that your freshwater fish might face. Look out for signs like spots, rotting of the edge of fins, lumps, swelling, missing of scales along with different minute behavioural changes that include buoyancy, loss of hunger and issue in breathing. Let’s study more about the possible diseases and their treatment, that might ease your fishkeeping.

Bacterial Infections


The most common bacteria that your fish comes across are Aeromonas salmonicida, Vibrio and Edwardsiella. This occurs in your fish especially when they face any kind of injury. It may so happen that your fish is fighting with other fishes, or got a cut from the substrate’s sharp edge, then their injury may not heal in some situations. This mostly happens when the water quality is low and they are not getting enough food even after sustaining the injury. This stress reduces the capacity of their immune system and gradually supports the setting in of the bacteria.

While your fish gets infected with the bacteria, they develop blood-red spots on their body, loss of appetite, ulcers over gills and their eyes get enlarged.

Apart from this, there is a Mycobacterium spp infection which is also known as “Fish Tuberculosis”.


The fish needs to be quarantined at the time of treatment. Keep the tank clean with all feasible satisfying parameters. You can consult a veterinarian and provide them with the necessary antibiotics. Unfortunately, Mycobacterium has no proper or potential cure.

Poison of CO2


Carbon Dioxide dilution within the water is one of the most unwanted happenings within freshwater aquariums. This dilution can cause severe illness to your fishes even when oxygen is present at an optimum level. A level above 30 ppm turns out to be deadly to the fishes. This mainly occurs owing to the injection of CO2 within aquatic plants. The main reason behind this issue is that the CO2 reactor might be deactivated or the plants are unable to absorb the proper amount of CO2 because of heavy lighting. Poisoning of a whole fish can occur due to this, which can even end your fish’s life.


You can make use of air stone for agitating the surface of the tank. This will genuinely help in the dissolution of the whole CO2 volume from the water.

Parasitic infections


A parasitic infection is the most common of all fish diseases within a freshwater tank. The notably known names are White Spot Disease or Ich, Flukes, Costia, Anchor Worms and even fish lice. The common symptoms of being infected are bruises and loss of appetite. Sometimes, fishes even lose their scales.

Surprisingly, parasites pave their way to a tank mainly when any new fish is being introduced. Generally, parasites are not found in the fish body as the consistent immunity within keeps them from affecting the fish. However, stress, transportation or a completely foreign residence might induce parasites inside the fish.


The treatment will depend on the type of parasite that has captured the body of the fish. However, there are a few nitroimidazoles that help to complete elimination parasites from fish.



Caused through iridovirus, this disease can be easily confused with White Spot Disease as they develop small white coloured bumps, which are completely similar to Ich or fin ray fractures. These bumps might turn pink from white and can occur in any part of the body, including fins.


Though not severely fatal, sadly, this disease does not respond to any kind of treatment as such. You can still consult a veterinarian for getting to know whether it is actually White Spot or Lymphocystis. According to the vet’s recommendation, you can change the water condition or diet routine for helping the fish to recover from prior discomfort and illness.


Dropsy disease causes bloating of the body and protrusion of scales within the fish. This is caused by bacteria within the kidneys of the fish, that results in building up of fluid continuously. The belly of the fish swells up and the eyes bulge out. The most notable sign of the disease is that the spine becomes curved along with reddish colouration of the anus.

Unfortunate enough as a fish keeper to know that if your fish is diagnosed with Dropsy, it will eventually die. Yes, not immediately, but over course of time, the immunity system stops entirely and internal damage causes the fish to eventually die.

Hemorrhagic septicemia


Yes, may sound startling, but it’s true! Your fish can develop septicemia due to internal haemorrhage. The various symptoms include bulging of eyes, open sores, irregular movement and odd behaviour. The symptoms are usually visible. However, in some cases the disease is so deadly that in some fishes they do not even reveal any external signs.

The main reason for this disease is that any fish can bore this infection through a virus named Viral hemorrhagic septicemia virus. But, one carrier fish can contaminate the environment and gradually all the other fishes get infected.


It is to the utmost misfortune, that this disease has no cure as such. You can use a wide spectrum of medicines and antibiotics to reduce the death rate. Moreover, remove carbon and perform water change during treatment.

A little note to remember

There are several other diseases that can infect your fish. They might face ragged tail fin disease where the fins become ragged and discoloured. Apart from that, there can be fin rot disease, where the infected fish survive severe fin nipping. Yes, they all suffer but it can be brought to minimum with your quick notice and care. Do not experiment or perform guesswork on your pet, rather immediately consult a veterinarian.

You can treat your fish with antibiotics, salt solution or other proper medication. Still, remember to provide a proper tank and fulfil the water requirements along with diet. It is a pivotal point to keep your fish safe and secure.