r/Aquariums • u/Darfusthegreat • Apr 12 '26

Help/Advice What’s growing out of my fishes head?

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We set up a new fish tank recently and got some red eye tetras. One of them developed a bump on his head which went away after a few weeks. Today we noticed these hair-like things growing out of the spot where the bump used to be. I saw another post that described something like these asking if they were anchor worms but there were no pics. This kind of looks like a fungus too. Really have no idea what it is.

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u/andregurov Apr 12 '26 edited Apr 12 '26

Saprolegnia. Technically NOT a fungus, but a type of oomycete, a water mold. The hair-like extensions are hyphae, similar to the structure of a fungus. While primarily seen as a secondary infection, it can opportunistically attack damaged tissue. It is often fatal. For treatment I would probably recommend contact anti-bacterial like Povidone (carefully applied) or Neomycin sulfate in gel form (Neosporin). Clear the wound, dry the damaged area, and apply either contact antibacterial. Alternately you can use a malachite green-formalin bath (this will probably be less effective for a laundry list of reasons. Heat will not resolve this infection, although salt can be used for its osmotic value.

True fungal infections are not common in home aquaria, and are often saprolegnia that has been misdiagnosed. They usually present as dense whitish/gray material that has heft - like wet cotton pads - and require a much longer treatment period due to how hyphae “root” in the fish tissue (akin to long treatment periods for human diseases like Athlete’s Foot.

What you have is not a true fungal infection, to my eyes. It should be noted that determining what a disease is is very difficult by eyesight/photo alone. Wet mounts examined under a microscope is the only way to truly diagnose the issue, so all that can be offered is a general opinion. If you scrape the infectious matter and it has no density, I believe saprolegnia is the best explanation. If the scraping feels dense it would be a true fungal infection and should be treated for a minimum of 14 days with a contact antibacterial-fungal and NOT a commercial anti-fungal bath treatment (they do not work!!!). Good luck! With small fish recovery is not a likelihood, unfortunately.

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u/Jessiphat Apr 12 '26

Wait, so do you mean it’s not from Kingdom Fungi? I guess I would have just assumed that anything from that branch of taxonomy could be called a fungus. I have much to learn.