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Most Common Bacterial Infections in Aquarium Fish

Most Common Bacterial Infections in Aquarium Fish

Nobody wants their fish to be sick. Being able to identify the different types of infections and sicknesses that your fish could catch will only help you better prevent or treat them if they were to occur. While there are numerous infections and diseases that your fish could be suffering from, we have put together an informational list of the most common bacterial infections in fish. Hopefully, this will help you treat your fish if they are sick or prevent them from ever suffering from these infections in the first place.

Mouth Rot

This bacterial infection usually begins with small white or gray marks on the head, fin, or gills of the fish. The lips of your fish may also have small white or gray marks as well. The lesions or marks grow over time if you do not treat this, while also becoming white and fluffy. It is important to note that there is a difference between whether the mouth rot is bacterial or fungal. An infection from bacteria can be identified by the lesions being coarser and grayer in color.

It is important to note that what we explained above is the chronic form of mouth rot. There is an acute form of mouth rot, but what that entails is instances when a fish dies suddenly and is diagnosed with mouth rot post-mortem.

Fin Rot

If you have identified that your fish has red streaks on their fins, as well as having abnormal lightening on the edge of their fins, then it is most likely a sign of fin rot. The red streaks are indicative of the fin membrane fraying and or rotting. This disease comes from bacteria that is in the water which infects a fish when they have injuries, or when the fish feels stress.

When this is not found or treated, it can have severe effects on the fish, such as the fin completely rotting or it spreading to its whole entire body. Not properly caring or treating this disease, as well as never identifying it, can lead to fish death.


This bacterial infection also includes an acute and chronic form of the disease. It is important to note that symptoms of this bacterial infection include higher or increased respiration, loss of appetite, lethargy, and skin hemorrhages.

  • Acute Form— This is when death randomly or suddenly occurs before you have seen any signs or symptoms of this disease. When a post-mortem exam is done, enlarged organs are often an indicator that this is what the fish suffered from.
  • Chronic Form—This is also identified when the fish dies and when ulcers and exophthalmos are identified in the post-mortem exam.

It is important to note that this disease is most often found in marine or brackish water, but it can also occur in tropical species.

Skin Ulcers

Skin Ulcers are any raw and open area on the fish’s skin. This infection might also coincide with other symptoms as well; however, if you observe the open and raw sore, it is typically a skin ulcer. Fish tend to suffer from this type of bacterial infection when they have a wound or skin injury and there are bad bacteria found in the surrounding water which invade the sore.

Treating this fish does not only include antibiotics to help the fish feel better, but also anti-fungal baths to treat the ulcers. Improving the water quality can help this bacterial infection as well.

Fish Tuberculosis

Observing that your fish is not eating as often or as much as usual, seeing their color fade or become paler, or just thinking that they seem as if they are sick or in poor health overall could be signs that your fish is suffering from fish tuberculosis. You fish may be suffering from this because there were bacteria from another infected fish, or due to the presence of a dead or dying fish in the tank that has these bad bacteria present. However, it is important to note that this disease is not highly contagious, but if the fish is stressed and this bacteria is present, then it is way more likely to make your fish sick.

Not treating this disease for whatever reason can result in skeletal deformities for your fish, which directly result in a low quality of life. Death is also an unfortunate result of this bacterial infection if left untreated.

Having a pet fish and caring for the aquarium can be a large responsibility. Educating yourself and knowing the best course of action in case something goes wrong is always recommended. That is why looking at these most common bacterial infections in fish can help you properly prepare if your fish does unfortunately become ill. These five bacterial diseases in fish are some of the most common infections that you fish can suffer from. Yet, it is important to note that there are indeed other ones that we did not mention above.

Almost all these bacterial infections that can cause your fish to be ill come from bacteria being present in the water due to poor water quality or poor conditions in general. This shows how important proper maintenance is for your tank or aquarium. Not caring for the water and the environment properly can be extremely harmful to all the tank inhabitants. It is also important to know that observing your fish regularly can help you identify any issues that arise early on so that you do have the ability to treat whatever issue is occurring.

With all this said, if your fish is suffering from one of these bacterial infections, we are here to help! Here at eFishMox we sell several fish antibiotics that can help combat and treat the bacterial infection that your fish is suffering from. Whether you need to buy fish cipro, fish amoxicillin, or any other fish antibiotic, we have it available for you. Search our website and reach out to our skilled professionals to purchase the medicine that can best help your fish!

Most Common Bacterial Infections in Aquarium Fish

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