How Can I Eliminate Fungus From my Pet Fish?

Hello, my name is Tammy and I have a four-year-old Oscar named Big Boy. I have been treating him for a fungal infection for almost...


Hello, my name is Tammy and I have a four-year-old
Oscar named Big Boy.

I have been treating him for a fungal infection for almost a month now.
Just when he starts to improve he has a set back the next
day. He now has it in his mouth, but he is hanging
in there. I hate to give up on him because he isn’t
ready to give in.

I have been treating him with
malachite green for almost a week, but he still
has labored breathing and an infection where
he recieved a cut as I was transferring him to
another tank. That is really when it all started.

The fungal infection looks like cotton one day and
then spores sprouting off of it then next. Now,
there is little spore sprout on the top of his
head, but cotton still in his mouth. Could you
give me any instructions? What would be the
correct amount of malachite for a 50 gallon tank?
I have been using 1 teaspoon per 10 gallons.

Batavia, N.Y.

I realize that questions about aquarium fish are a bit off-topic here on Catster and Dogster, but it sounds like Big Boy really needs help. Since anyone reading this is bound to be an animal lover, I hope nobody will mind if I stray from furry friends to aquatic ones for a single post.

Fungal infections in fish are often opportunistic. They frequently take root in areas where the skin has been damaged. I am not surprised that Big Boy’s infection began when he was accidentally traumatized.

Based upon your description, it sounds like Big Boy is suffering from cotton wool disease. Cotton wool disease is caused by a variety of fungi that infect the skin, mouth, and gills.

Malachite green is a treatment for cotton wool disease and other fungal infections. However, malachite green has a low margin of safety and may be dangerous to humans. Rather than treating the entire aquarium, consider bathing Big Boy in a more concentrated solution (4 teaspoons per gallon of water) for 30 seconds one time. Be careful not to expose yourself to any water containing malachite green.

Another option is treating with salt water baths. Big Boy can be placed in a bath containing one teaspoon of aquarium salt (don’t use table salt) per gallon of water for 30 minutes (if Big Boy shows signs of distress, remove him from the bath immediately). This treatment can be repeated every other day.

Please be aware that either of these treatments can cause stress and may be difficult for Big Boy to withstand. You will be fighting an uphill battle to make him better.

Nursing care is very important in cases of cotton wool disease. Pay special attention to water quality. Measure pH (ideal is 7.2), nitrites (ideal is 0), nitritates (ideal is less than 10 parts per million), and temperature (maintain between 72-85 degrees Fahrenheit) daily. Provide adequate oxygenation. Remove all decorations from the tank until Big Boy is cured (decorations can harbor fungal spores). Soak the decorations overnight in a concentrated salt bath before returning them to the tank when he is well.

Change 20% of the water in the tank each day. Be certain to match the temperature and pH, as well as remove chlorine and chloramines from the water before adding it to the tank. Feed a diet that is designed specifically for Oscars. Do not allow leftover food to remain in the tank–it will have devastating effects on water quality. Use a state-of-the-art water filter. Provide 12 hour cycles of light and darkness that mimic the conditions of the tropical rain forests where Oscars naturally live.

I hope Big Boy is able to recover. Please let me know how it goes.

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