Fish Disease in Tropical Freshwater Fish Tanks Aquariums – Fin and Tail Rot

Fin and Tail Rot is a common infection in tank aquariums caused by a group of bacteria called Cytophaga, which affect fish with long, soft fins. The symptoms have a wide range. Generally the tail and fins start looking ragged, either in the form of a ‘bite’ or a ‘shredded’ effect. These lesions are discolored White/Grey with an edging of red. They can form into ulcers which have an orange/yellow color. The fish may also be listless and reluctant to feed. At an advanced stage, large milky patches can be seen on the fins and a sizable amount of tissue will have been destroyed. Respiration will also be rapid with excessive amounts of mucous in the gills and the lips of the fish may be swollen. The main danger is that if left untreated, the disease can rot the entire fin and start to invade the fish’s body.

Causes and Prevention

It is very important to diagnose why this infection has occurred. The bacteria actually exists in most fish tank aquariums without being a problem, therefore the disease is usually triggered by other factors, virtually all cases being precipitated by stress or poor environmental conditions. It is essential to identify and remove underlying stressors.

It is commonly introduced into tank aquariums by new fish from the pet store that harbour the harmful bacteria, which they release into your tank through feces. It is therefore vital to quarantine all new fish for about 10 days before introducing them into new fish tank aquariums. Fish can be extremely sensitive to stress and can also develop the disease due to the trauma of not being carefully acclimatized to a new fish tank environment. It is important that all fish are compatible and peaceful fish are not matched with aggressive fish, as this would lead to bullying which usually results in fin and tail nipping and the wounds provide ideal breeding grounds for the bacteria. Also do not overcrowd tank aquariums as this stresses out fish and can even make peaceful fish become nippy, as well as resulting in polluted tanks.

To identify and remove any problems with water condition, do a check of your water quality using a test kit to ensure there is no build up of unwanted chemicals. Make sure you maintain the proper water parameters particular to the fish species you keep. Hard water with a high pH encourages the growth of the bacteria, as does a sudden dip in temperature.

As part of your regular maintenance routine, ensure all equipment is working properly, especially the filter. Do 15% water changes weekly as well as vacuuming the gravel. You should also try to remove any uneaten food after each feeding time.


Before using any medication, do a thorough clean of the fish tank. Scrub the inside of the glass/acrylic and thoroughly clean the gravel to remove waste from the substrate. Alternatively, you may completely remove the gravel for greater effect. You should minimize the areas where the bacteria can live and breed so take away any ornaments in the tank and bleach them. Clean the outside of the fish tank, hood, light and tank top. Water quality plays a critical role in the prevention and cure of fin and tail rot so you need to perform a large water change – I would suggest 50%. Remove activated carbon from filters as this will eliminate any medication you use.

There are different degrees of fin and tail rot which will determine the type of treatment you use in your tropical freshwater aquarium.

For the first stages of the disease, I strongly advise using Melafix along with aquarium salt. This is an all natural medication which will not destroy your biological filter. Use 2 teaspoons (10ml) of Melafix for every 50 gallons of water, combined with 2 tablespoons of aquarium salt per 10 gallons of water. Regular tropical fish will be fine with it. Dissolve the salt in water rather than pouring it into the tank, as if it comes into direct contact with fish it will burn them. The water will foam up and smell of liquorish but this is normal and will soon disappear after the treatment is over and you perform water changes. Perform a 5% water change each day for 10 days and replenish the medication and salt according to the correct ratio to bring the concentration back up to full strength. Continue to keep the tank clean by wiping the sides and vacuuming the gravel (if you keep it). This will treat the bacterial infection and help to heal the damaged fins. You should notice a rapid improvement and regeneration of fish fins. If not, the fish need to be removed to a quarantine tank for stronger treatment.

I would just mention that some advocate using copper sulfate but this risks further damage to the gills of the fish.

For more advanced forms of the disease I would recommend moving the infected fish into a spare, bare tank for treatment. You will need to treat the fish with antibiotics such as Tetracycline, Maracyn-Two or Maracyn Plus Antibacteria for at least 10 days. Carefully follow the instructions and do not mix medications as this can be fatal. These medications are available from pet shops and online vendors.

Keeping fish tanks, aquariums disease-free

Following a protocol of quarantining when adding new fish and carefully acclimatizing them to new tank aquariums, as well as suitably matching fish and avoiding overcrowding, will greatly minimize stress, which is a major cause of the disease. Through regular and thorough maintenance of fish tank aquariums, ensuring good water quality, correct water parameters and efficient filtration, incidence of parasites becoming a problem should be eliminated. Should fin and tail rot occur despite your best efforts, early signs of the disease can be easily detected by carefully monitoring your fish each day, especially at feeding time. Through swift remedial action, fish can be quickly treated and restored to health.

Jill writes concerning some of the dangers encountered maintaining a Freshwater Aquarium []. For additional information on fish care visit her website dealing with different types of Fish Tanks [].

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