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Q&A: Why Does My Betta Have a White Sore on His Tail?

Dr. Mark is a veterinarian with over 40 years of experience in the field. He works with dogs, cats, exotics, and livestock.

White sores on Betta tails are usually caused by a fungal infection.

White sores on Betta tails are usually caused by a fungal infection.

What Is This White Sore on My Betta's Tail?

"My Betta has a white sore on his tail that has increased in size in the last week. I noticed a spot on his tail a few weeks ago and was advised to do a 50% water change and add aquarium salt and catappa leaves to his tank (by a local fish store), but this hasn't worked.

I've been researching online, but I'm not sure what it is, as it fits a few different descriptions. He is in a 6-gallon tank. He is acting normal. I'd really appreciate any advice." —Mary

Methylene Blue for Fungal Infections in Bettas

If you had not tried the water change and the salt and catappa leaf treatments for bacterial and fungal infections, that is what I would have recommended first. Since it has not worked, there are several other possibilities.

The first possibility is that the fish does have a fungal infection and just needs an alternative treatment. The leaves do not always work. There are several alternatives available because nothing works all of the time.

How to Do a Methylene Blue "Dip"

Since the fungal infection is not responding to the catappa leaves, you can try methylene blue. (You can probably find it at the fish store where you bought the leaves.)

There are several treatment methods described, but since your fish has only one evident spot, I recommend putting him in a bowl for a methylene "dip" (i.e., treating the affected area with a stronger solution than you would add to the entire tank).

  1. Thoroughly clean a glass bowl. (Do not use a plastic bowl.)
  2. Add 8 cc of methylene blue and one gallon of water to the bowl. (If you only need enough for a small bowl, make less but be sure to measure the amount of methylene blue with a syringe so that it is not too much. It is a relatively safe compound but can be toxic to your Betta if it is too concentrated.)
  3. Put him in the bowl and count to 10.
  4. Return him to his normal aquarium.

If you have not seen improvement in about 10 days, it is okay to repeat this. If the white spot is growing instead of getting better, you will want to try another alternative fungal treatment or look at the next alternative.

Below is a short video showing how to use methylene blue as a dipping mixture.

Fin Ray Fractures in Bettas

Another possible cause of the white sore on his tail is a fin ray fracture. Fin rays are used for opening and closing the fin to move around and probably also for a Betta to touch and be aware of his environment. (1)

Although they usually heal up without incident, the white mass on his dorsal fin may be a secondary fungal infection on the area that was originally injured.

Consult a Veterinarian

I am not sure where you are located, but in some regions, there are veterinarians that specialize in fish diseases and treatments. If things do not clear up with the alternatives I have listed above, you might need to check for a person in your area that works with fish.

Source

(1) Williams R 4th, Neubarth N, Hale ME. The function of fin rays as proprioceptive sensors in fish. Nat Commun. 2013;4:1729. Williams R 4th, Neubarth N, Hale ME. The function of fin rays as proprioceptive sensors in fish. Nat Commun. 2013;4:1729. https://pubmed.ncbi.nlm.nih.gov/26347560/

This article is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from your veterinarian. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2022 Mark dos Anjos DVM