Melatotaenia Praecox With Ulcer/lesion On Side

Dear all,

I have a very worrying fish with a clear lesion on the side of its body. Below is a picture with my questions.


190 L/50 gallons, has been running for over a year now. It has a filter and heater. Temperature is 24 C (75 F).

- 6 Melatotaenia praecox (dwarf rainbowfish)
- 2 swordtails
- 9 zebra danio's
- 3 apistogramma cacatuoides ( 1 male 2 female )
- 1 bristlenose pleco
- 6 chorydora (false) julii
- 2 dojo loaches
- 6 amano shrimp
- 6 nerite snails

25% water change every two weeks. I do not treat my water with anything. I do add fertilizer though. I vacuum the sand every other water change.


I'm out of test strips. Will try getting them tomorrow.

I feed my fish every day. Frozen bloodworms, flakes, some sinking pellets and duckweed for the rainbows.

Illness & Symptoms
I've had the rainbows for 2 months now. I noticed symptoms a week ago and it has gradually gotten worse. It looks like a sort of ulcer protruding from the side of the fish. It's only 1 spot but it's clearly red and elevated.

The fish in question behaves normally. Swims normally, eats normally etc.

So my questions:

- I've read this might be due to tuberculosis or some other form of mycobacteriosis. Is this the case?
- > if so should I be worried about TB transferring to me if I have a wound on my hand?
- Is it contagious, should I quarantaine the fish in question?
- What can I do to treat it?

melatotaenia praecox lesion side.JPG

If you read this and you have encountered these symptoms before please let me know! I'm extremely worried about this tank!
Take a deep breath & relax a bit. It doesn't look like fish TB. Its probably a non-lethal viral growth. Research Lymphocystis.
If you have a QT tank, be a good idea to remove the infected fish. Lympho. is contagious to weakened fish.
Consider upping your tank maintenence to a 50% WC each week. Lymphocystis can diminish over time if the infected fish's immune system strengthens.

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