4 Common Fish Diseases: How to Avoid Them

fish disease

Fish doesn’t survive for many years in the wild when compared to living in the aquarium, but don’t be deceived because your aquarium can also be a hotbed of diseases that will cut short your fish’s shelf life. 

Most of the time, the quality of your aquarium water will affect the health of your fish and the number of diseases that can be generated will blow your mind, let’s sample some of them below. 

4 Common Fish Diseases

1. Cotton Mouth

Columnaris is the disease’s scientific name and the infection is caused by the Gram-negative rod-shaped bacterium Flavobacterium columnare. This type of bacteria will get into your fish via the gills or mouth; also if your fish has small wounds then it will become infected. What’s worse is that the bacteria will live in water for up t 32 days with 50ppm of water hardness. 

If you want to avoid the growth of columnaris, do not overcrowd your fish tank, and ensure that the oxygen levels are as recommended. And as you take care of your fish ensure that you keep a close eye on its physical appearance, if you notice cloudy fungus-like patches or ulcerations on its skin then you know that your fish has been infected with cottonmouth. 

Also check for the accumulation of mucus on the dorsal region, gills or the head, the gills may also change color to dark or light brown. 


The guidelines offered for treating your fish in this excerpt are not conclusive and a vet should be consulted. So, to get rid of the disease you could use a combination of antibiotics, or expose your fish to a medicated fish bath. Internal infections could be tackled with medicated food and the adult fish and fry can be treated by applying copper sulfate, hydrogen peroxide or potassium permanganate.

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In order to prevent the disease from being a menace you could vaccinate the fish, and this can also be done before the fish gets infected. 

2. Slime disease

Fish’s infected with the slime disease will exhibit a white/grey or blue mucous coat, because of this the fish skin becomes excessively irritated and you will notice that it will scratch itself against solid objects inside your aquarium. 

The fish will rarely eat and will thus become stressed; in severe cases, the fish will develop fin rot, and some may feature some physical damages on their skin. Worse still, the fish might develop other secondary infections. 

How to avoid slime disease

Do not overcrowd your aquarium, ensure to maintain good water conditions and offer nutritional foods to your fish. Remember fish are very delicate and keeping them in captivity means that you have to provide the conditions that they are used to in the wild. Therefore, things like sudden shifts in water temperature should be avoided. 


Your fish’s life is in danger if the mucous coat will take over its gills, as they will most probably suffocate and die, thus the need for quick medical attention. The first step, however, would be to separate the sick fish from the rest of the population, use an antibacterial agent such as Formalin or Furan 2, and ensure that you change your tank water before treating the tank.

Filter carbons should be removed before the addition of medication, also, provide high-quality feed with vitamin supplements to your fish. And for the slime coat, you could add a stress guard or stress coat that will assist in healing the fish. 

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3. Hole in the Head


Aquarists who rear discus, cichlids and the Oscars type of fish should keep an eye out for this type of disease. The exact cause of the condition is yet to be established but it is highly believed that the flagellate parasite Hexamita travels through the intestinal tract to other parts of the fish’s body including the kidney and spleen. 

With the slow progress, lesions of holes will begin to appear in the fish’s head, and after they open up parasitic larvae that are characteristic of small white threads will be discharged. If care is not taken secondary fungal or bacterial infections will manifest in the openings and lead to the development of other serious ailments or even worse death. 

How to avoid holes in the head

The most common factor that aquarists need to look into is the quality of water, provide your fish with a proper diet and don’t crowd your fish tank. The disease mostly affects older fish and it is thus believed that a decrease in the functionality of the fish’s immune system is a catalyst to the prevalence of the disease. 


Antibiotics could be added to the fish tank, feed your fish with vegetables and frozen meaty foods, also lightly steamed broccoli could help. Always utilize a separate treatment tank and be sure to act on the symptoms the moment they appear. No one method is guaranteed to treat your fish and you should thus seek the services of a qualified professional. 

Also, ensure that your water quality is up to par and that your fish gets the right dose of mineral and vitamins supplement. 

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4. Ulcers 

Ulcers fish

The moment you notice that your fish has developed skin ulcers then you have been doing a poor job in providing the right aquatic environments to your fish. You might notice that your fish has open sores on its body surface that are characteristic of a pink-red color and a white border that mainly consists of dead skin tissue. 

The seriousness of the ulcers is when it extends deep into the muscles of the fish and its internal organs. To note the development of the ulcers you should pay attention to the fin base, at times the ulcers might occur on the fish’s eyes or at the mouth cavity.


Ulcers normally develop through bacterial infection, and an interesting fact about this type of infection is that the bacteria might be present in water (naturally) and will remain dormant until the water conditions become intolerable. Other probable causes of the ulcer are if your aquarium fish sustain injuries from other parasites. 


They say prevention is better than cure, you should, therefore, ensure that your tank features a proper filter, avoid overcrowding and carry out regular aquarium maintenance practices. Antibiotics should also suffice in the treatment of the ulcer, what’s more, is that you can use other herbal remedies.

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