Fin Rot in Fish: Causes, Symptoms & Treatment

Imagine a vibrant aquarium filled with elegant fish gliding gracefully through the water, their colorful fins flowing like delicate silk. But what happens when those once magnificent fins become ragged and frayed, robbing these aquatic beauties of their splendor?

Fin rot a common and distressing ailment that affects many species of fish. It is a common in both freshwater and saltwater fish, causing the delicate fins to deteriorate and wither away.

From vibrant bettas to graceful angelfish, no underwater dweller is exempt from the clutches of this insidious disease.

But what exactly causes fin rot? How can one identify its symptoms? And most importantly, what are the effective treatments available to nurse these unfortunate creatures back to health?

In this comprehensive article, we will dive into the depths of fin rot exploring its causes, recognizing its symptoms, and discovering the best ways to combat this menace in our beloved fishy friends.

Tail rot of fish
Image: Tail rot of fish; Source:

What is Fin Rot in Fish?

Fin rot is a common and distressing condition that afflicts many species of fish, both in the wild and in aquariums. It manifests as the gradual deterioration of the delicate fins and tails, leading to fraying, shredding, or even complete loss.

This affliction not only compromises the beauty of these aquatic creatures but also poses serious health risks. While it may initially seem like a mere aesthetic concern, fin rot can quickly escalate into a severe infection if left untreated.

Understanding what causes this debilitating disease and how to identify its symptoms is crucial for fish enthusiasts and caretakers alike in order to ensure the wellbeing of their beloved underwater companions.

Causes of Fin Rot Disease in Fish

Fin rot is a common disease in both freshwater and saltwater fishes caused by a variety of factors, including poor water quality, injuries, and bacterial or fungal infections.

Bacterial Infection

Fin rot is a common disease in fish that is caused by a bacterial infection. Pseudomonas fluorescens is mainly responsible for fin rot disease in fish.

Researchers found three bacterial species Aeromonas, pseudomonas and vibrio caused fin rot in different fish species

A study found Pseudomonas fluroscens & Pseudomonas anguilliseptica caused fin rot in Nile tilapia (Oreochromis niloticus).

Pseudomonas fluroscens
Source: Researchgate

Flavobacterium columnare is also considered the etiological agent of fin rot disease. The bacteria can enter the fish through open wounds or through the gills.

Unsanitary Condition of Water

One of the most common causes of fin rot is poor water quality. If the water is polluted or contains high levels of ammonia or nitrates, it can lead to infection and disease.

Lack of dissolved oxygen, overcrowding and dirty and muddy water aggravate the disease.


Fish can also develop fin rot from injuries sustained while fighting or swimming in tanks with sharp objects.

Bacterial and fungal infections can also cause fin rot, and these infections are often difficult to treat.

Poor Nutrition

One of the most important nutrients for fish is vitamin C, which is essential for their immune system.

A lack of vitamin C can lead to fin rot and other diseases. A diet that is low in vitamins and minerals can lead to health problems in fish.

Transmission of Fin Rot Disease

The transmission of Fin Rot occurs when the bacteria responsible for the disease gain access to the fish’s damaged fins. This can happen through direct contact with contaminated water, substrates, or tank decorations.

Bacteria can also be introduced into the aquarium by new fish, plants, or equipment that carry the pathogens.

Signs and Symptoms of Fin Rot

Fin rot in cultured fish pond
Image: Fin rot in cultured fish

-The first sign of fin rot is usually fraying or rotting of the edges of the fins. The affected fish showed lesions and erosion on the tail and fins.

-The fins may also become discolored, swollen, or covered with heavy slime. Loss of appetite, weight loss, sluggishness, and erratic swimming.

-The sick fry swims close to the surface of the water in the puddle, loses its balance on its caudal fin until it becomes unraveled, flipped over, and sinks to the bottom.

-In small fingerlings, the pectoral fins most typically are infected first, the dorsal fins afterward, and infectious disease may be widespread between the fins ultimately if they are not as badly affected.

-Progressive shrinkage of the anal and dorsal fins’ ends was observed. The edges of fins turn dark, and fins start to fray.

-Microscopic analyses exhibited skin hemorrhage, skin ulcer, epidermal hyperplasia accompanied by dermal fibrosis, hyperemia, and hemorrhage.

How Do You Diagnose Fin Rot in Fish?

Tail rot in fish
Image: Tail rot in Tilapia

Diagnosing Fin Rot in fish involves careful observation of the fish’s physical symptoms and behavior. Here are the steps to diagnose Fin Rot:

  1. Visual Examination:
    • Look closely at your fish. Fin Rot typically starts at the edges of the fins and appears as fraying, splitting, or ragged edges.
    • Check for discoloration in the affected fins. They may become pale, white, or even reddish in color, depending on the severity of the infection.
    • Erosion in fin and caudal peduncle region and in trunk region small red or purple spots and ulceration were observed during this observation.
    • In artificial infection, within 3-10 days lesions in fin and skin tissue were observed and die with 2 months.
  2. Behavioral Observations:
    • Note any changes in your fish’s behavior. Fin Rot can cause stress, which may lead to decreased activity, reduced feeding, and hiding.
    • Fish may appear lethargic, have clamped fins, and exhibit abnormal swimming behavior.
  3. Tank Water Assessment:
    • Test the water parameters in your aquarium, including pH, ammonia, nitrite, and nitrate levels. Poor water quality can contribute to Fin Rot and should be addressed promptly.
    • Ensure that your aquarium’s temperature and filtration system are appropriate for the species you’re keeping.
  4. History and Tank Mates:
    • Consider the fish’s history and tank mates. If the affected fish has recently been introduced to the tank or has been in contact with aggressive tankmates, it may be more susceptible to fin injuries and infections.
  5. Microbial Examination:
    • In laboratory examination, it is found that fin rot symptoms caused some physiological disturbances such as; lowered hematocrit, hemoglobin and total plasma protein. Besides it increases immature red cells and neutrophils in the blood.

How To Treat Fin Rot in Fish?

The first step is to identify the cause of the damaged fin rot. If it is bacterial, the best fin rot treatment is to treat your fish with antibiotics.

If the cause of the fin rot is poor water quality, you will need to take steps to improve the water quality in your tank.

1. Antibiotics Medication

In most cases, antibiotic treatment can be used to treat fin rot if it is infected early. Oxytetracycline, erythromycin, streptomycin, kanamycin, and nalidixic acid were the drugs of choice for the treatment of fin rot.

2. Formalin

Formalin and malachite green are used for proper disinfection. One way is that the two chemicals can be used together as a dip.

This combination helps to kill the bacteria that cause the disease, while also helping to heal the fins.

3. Copper Sulphate

Copper sulfate solution (1-20,000) bath for 10 to 10 minutes has actually been found to cure the fish at the early stages of the disease but curing these remains to be impossible.

4. Salt Bath

Salt baths are a popular treatment for fin rot, a bacterial infection that causes lesions and deterioration of the fins. The salt bath helps to clean the wound and speed up the healing process.

It also creates an environment that is unfavorable for bacteria to grow. In addition, the salt bath can help to reduce inflammation.

5. Remove Sharp Objects

Inspect your aquarium for sharp decorations or objects that could potentially injure your fish. Smooth or round edges are safer for their delicate fins.

How To Prevent Fin Rot Disease

There are several methods for preventing fin rot disease, including regular water changes, maintaining optimal water temperature and pH levels, using a quarantine tank for new fish, providing a balanced diet, and treating any existing infections promptly.

Maintain Good Water Quality

Good water quality, consumption of small quantities of food, and constant water temperature all help prevent fin rot from afflicting the fish.

Ensuring that the tank is clean (for domestic species) can prevent the deterioration of fish fins.

Regular Water Exchange

Routine aquarium water restoration will ensure your aquarium always stays safe, while regular water testing can assist you to identify any type of water quality problems well before observing signs of bacterial contamination and fin rot.

Provide a Balanced Diet (Don’t Overfeed)

If your fish don’t finish the leftover food in the tank, leftover food can promote microbial overgrowth and ensure your catfish develop plague.

Overfeeding can lead to poor water quality and an increase in the amount of waste produced by the fish, which can increase the risk of fin rot and other infections.

The feeding time is also an excellent opportunity to carefully monitor your fish’s behavior. Keep an eye on any changes to its fins, tail, body, appetite, and behavior.

Quarantine New Fish

When introducing new fish to your tank, it’s a good idea to quarantine them for a period of time to ensure that they are healthy and not carrying any infections that could spread to your other fish.

Avoid Overcrowding

Overcrowding can lead to stress and poor water quality, which can increase the risk of fin rot and other infections.

Keep Your Tank and Equipment Clean

Regularly clean and disinfect your tank and equipment to help prevent the buildup of bacteria and other germs that can cause fin rot and other infections.

Fin Rot in Aquarium Fish Species

Betta Fish

Betta fish fin rot symptoms include:

  • Frayed or ragged fins: the edges of the fins may appear to be disintegrating or breaking off.
  • Discoloration: the fins may turn black or brown, indicating the presence of necrotic tissue.
  • Shortening of fins: the fins may become shorter and smaller as the disease progresses.
  • Redness or inflammation: the base of the fins may become red and swollen.


The symptoms of fin rot in goldfish include:

  • Frayed or ragged fins: the edges of the fins may appear to be disintegrating or breaking off.
  • Discoloration: the fins may turn black or brown, indicating the presence of necrotic tissue.
  • Shortening of fins: the fins may become shorter and smaller as the disease progresses.
  • Redness or inflammation: the base of the fins may become red and swollen.


Can fin rot kill fish?

Yes, fin rot can be serious and even deadly for fish if it is left untreated. Fin rot is a bacterial infection that causes the fins and sometimes the skin and scales of a fish to become damaged and eroded.

The infection can spread quickly and can lead to secondary infections, which can further compromise the health of the fish. In severe cases, fin rot can be fatal if not treated promptly and effectively.

How long does fin rot take to kill a fish?

It’s difficult to say how long it will take for fin rot to kill a fish, as it can depend on a number of factors such as the species of fish, the severity of the infection, and the effectiveness of treatment.

In some cases, fish with severe fin rot may die within a few days or weeks if the infection is not treated. However, if the fin rot is caught early and treated promptly and effectively, the fish may make a full recovery.

How contagious is fin rot?

The risk of fin rot spreading from one fish to another is generally higher in crowded or poorly maintained environments, where the fish may be more prone to stress and infection.

To reduce the risk of fin rot spreading, it’s important to maintain good water quality, provide a clean and stress-free environment for your fish, and isolate any infected fish from the others.

Can fin rot affect humans?

Fin rot is a bacterial infection that affects fish and is not known to be contagious to humans. However, as with any animal, it is always a good idea to practice good hygiene when handling fish or any other pets.

This includes washing your hands thoroughly with soap and water after handling fish or their tanks, as well as avoiding contact with any open wounds or cuts you may have.

It is also important to remember that certain species of fish can carry diseases that can be transmitted to humans, such as certain types of parasites or bacteria.

Can fin rot cause dropsy?

No, fin rot can’t potentially lead to dropsy. Dropsy is a serious and potentially deadly condition that is characterized by swelling, particularly in the abdominal area.

Dropsy is often caused by a bacterial infection or internal organ damage, and it is not a complication of fin rot.

Can fin rot heal on its own?

It is unlikely that fin rot will heal on its own without treatment. Fin rot is a bacterial infection, and left untreated, it can spread and become more severe.

The infected tissue will continue to deteriorate, and the fish’s fins, skin, and scales may become increasingly damaged.

Can fin rot spread to other fish?

Yes, fin rot can spread from one fish to another, especially if the fish are housed in close proximity to each other, such as in a tank or pond.

Fin rot is caused by bacteria, and the bacteria can be transmitted from one fish to another through contact or through the water in which the fish are living.

If you have a fish with fin rot, it’s important to isolate the infected fish from the others to prevent the infection from spreading. You should also clean and disinfect the tank or pond and any equipment that the infected fish has come into contact with to reduce the risk of the infection spreading to other fish.