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Treating infected/split fins


Tail or fin rot

Tail or fin rot is primarily caused by Aeromonas bacteria that gained entry to these powerful yet delicate bone and tissue structure. When caught early, the treatment is simple as described under treatment of ulcers. There are however times when the fins may be red with frayed areas or times when the problem is noticed when there are areas where the fins have been eaten away to a large extent. One of the tell-tale symptoms is where the fins have been destroyed in wide semi-circles from the edge, resembling large “bite marks”. One thing that is curious about fin-rot is that the bone rays as well as the much more fragile tissue between the fin rays are destroyed at the same rate.

If a fin remains white and the bony rays of the fin remains intact, but the tissue between the fin rays have been destroyed, chances are very good that the problem originated from a chemical burn and not bacterial activity. An example of this kind of burn can be overdosing with Formalin or the application of a salt paste or Potassium Permanganate paste to the fin. Take a moment to reflect on the appearance of the damaged fin and recent treatments.

Whatever the conclusion, the treatment should remain basically the same because you have to either treat for a bacterial infection or treat for the prevention of an infection. If the fin has lumpy red lesions and obvious dead or dying tissue on it, these lumps should be scraped off with a firm but blunt instrument like a putty knife or a teaspoon. Make sure the area is scraped clean, without causing unnecessary dammage.

The next step is to cut away the infected edges of the fin. While doing so try to remove as little as possible from the top and bottom rays of the caudal fin and also as little as possible from the leading ray of the pectoral fin. If the infection is already approaching the base of the fin, you may not have a choice but to remove a portion of the stronger rays. The probability that the fin will completely regenerate after severe amputation of the hard bony rays as mentioned above, will becomes les the closer the amputation is done to the base of the fin.



         finrot            finrott2




The whole area where infection occurred should then be sterilised, preferably not with a strong solution of Hydrogen Peroxide because it will do more damage than good. The preferred medication to use on fins are Finmed or Woundmed both distributed by Bao Bio, Wound Powder by Loolilocks or Pro-cure from Koi Water Barn.  Your koi dealer may also have a proprietary topical treatment that is not mentioned here. One can also use  Acriflavine-, Melachite Green-, Methylene Blue –solutions to sterilise the fin. Leave for a few seconds, dab it dry with a paper towel and seal with Friars Balsam or propolis. Make sure it is dry and if necessary, inject the fish with a broad spectrum antibiotic.


The photo above clearly demonstrates a caudal fin with bacterial infection. Fortunately there were no damage to the rays and tissue but what makes this infection serious is the fact that the bacteria have started to attack the root of the fin at the peduncle. In this instance the fish did not respond to topical treatment alone and it became necessary to scrape the infected area as described above, and also supplement the treatment with a series of antibiotic injections. It took seven weeks of isolation and treatment to restore the fish to full health in the fairly cool spring water temperature of 18 to 20 degrees Celcius.

Split fins

A small tear in a fin may occur through netting, especially if the correct net and netting technique is not used. Most fins are prone to tearing in such cases but the pectoral and caudal fins may need some treatment after such an incident. Normally these fins will neatly align and mend by themselves if the tear is not deep (to the base of the fin). It will however require that the fish be placed in a tranquil environment where it do not have to compete too seriously for food or are frequently startled.

If one of these fins are however torn to the extent that it is split right up to the root of the fin where it attaches to the body, the fin may also mend on its own accord but frequently a neat alignment will not occur, sometimes leaving an overlapping fin membrane or an abnormal wide membrane that will always be a distraction when viewing the fish.

Until a few years ago the most recognised method of treatment constituted suturing. This process requires skill and for us as semi dyslectics, it turned into a real battle against time and the expansion of our vocabulary! Jokes aside, suturing requires a fair amount of skill and is prone to cut through the fin. Suturing also did not hold up very well. When suturing for instance a split pectoral fin, it is sometimes necessary to apply it to two rays on each side of the split. The danger is then to make sure the two edges do not overlap when you pull it tight. One must also be careful when choosing the specific suture. Some absorbs before the fin is completely healed. The last aspect about suturing is the fact that it requires semi-permanent piercing that will keep a passageway open for bacteria to enter the fish and create additional problems.


More recently the trend to use Superglue to “repair” split fins have produced very satisfying results. It is a quick procedure and the two sides of the split holds very well. I have had only one incident where there was a need to repeat the procedure.

To use superglue, the fish should be anesthetized as described elsewhere on the web-site, and placed on a soaked towel. While a helper keeps the fish steady and restrained, use a paper towel or tissue paper to dry the edges of the split in the fin well. Do a practice run by aligning and pressing the two sides together.  When you are confident that the alignment will go smoothly, apply a thin layer of superglue to one of the inside edges of the split and press the two together. Apply topical treatment to the fin, inject it with antibiotics if necessary and release the fish. The superglue binds the two sides instantly and no drying time is required. This procedure is easy, quick and durable enough to allow time for complete healing.

Last Updated on Wednesday, 07 March 2012 22:20