Corydoras With Clamped Dorsal Fin, Sick?


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Hello everyone, I'm hoping someone can help me identify what's wrong with a corydoras of mine.


What is the water volume of the tank? 20 gal tall
How long has the tank been running? 2.5 months
Does it have a filter? Top fin 20
Does it have a heater? Yes
What is the water temperature? 72°F
What is the entire stocking of this tank? (Please list all fish and inverts.)
4 False JuliI cory, 5 zebra danios, 1 Honey Gourami


How often do you change the water? 1 week
How much of the water do you change? 1/3 to 1/2
What do you use to treat your water? Prime
Do you vacuum the substrate or just the water? I vacuum the sand substrate.

*Parameters - Very Important
Did you cycle your tank before adding fish? Danios were in for cycle, the rest added later.
What do you use to test the water? API Master test kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.


How often do you feed your fish? Once a day.
How much do you feed your fish? About how much the danios/ gouramI eat in a minute plus a cory wafer or two.
What brand of food do you feed your fish? Tetra flake, tetra cory wafers
Do you feed frozen or freeze-dried foods? No

Illness & Symptoms
How long have you had this fish? 1.5 months
How long ago did you first notice these symptoms? A week or two
In a few words, can you explain the symptoms? Clamped dorsal fin, hides, tail curves up when resting.
Have you started any treatment for the illness? Water changes.
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all? The clamped dorsal fin, seems to be hiding more often. Still comes out to eat and occasionally swims with other corydoras.

Long story short, my smallest corydoras has started to hide more often and has a clamped dorsal fin. He does seem to still come out an eat and swim with the others, but not as often as he used to. Also sometimes he rest with his tail curved upwards or to one side, not sure if this is a normal behavior.

I don't see any other visible signs of sickness and his poop is still pink colored.

I have General Cure and Melafix on hand, but I'm hesitant to treat without knowing a cause. I don't have a quarantine tank.

Thanks in advance!


Fishlore Legend
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Holland (The Netherlands)
More than 10 years
Mmmm I don't like the reddish color.
Looks a bit like an internal bacterial infection to me.

I don't know what caused it. It might be an idea to variate a bit in food (frozen/freeze dried).

I've had my suspecions about Tetra food earlier as staple food. It might lack certain minerals / proteins. But that is just a thought.

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