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Please excuse this English-language post -- my German is not very good!

I have a group of 8 Corydoras duplicareus in a 60-litre tank. Water quality is good -- no ammonia, no nitrite, 20ppm nitrate, pH around 6.

Recently some individuals don't seem well. They are a bit lethargic and have protruding scales, but no body swelling. The protruding scales don't seem to last very long -- after a day sometimes the fish go back to appearing normal. They are still eating, but not as well as in the past.

One thing that is obvious is some fish have bulges at the base of the dorsal fin, on both sides. These are about 2mm high and 4mm long. The bulges don't appear to have colour, but one of them is whitish on one side of one fish. The bulges seem to be "permanent", as in they don't come and go like the protruding body scales.

I recently had some Corydoras sterbai in another tank that died slowly one by one. I could not figure out what was killing them, there were no obvious symptoms except general lethagy, but on their last day of life each became entirely covered in what looked like a thin layer of whitish fungus. I treated the last couple of fish with Metroniadazole, praziquantel and erythromycin over 5 days, and now they look good. I am concerned that the duplicareus have the same thing -- whatever that was.

Does anyone have a good idea of what this might be? Should I just treat the duplicareus with the same antibiotic combination as seems to have worked for the sterbai?

I HAVE ATTACHED TWO PHOTOS OF THE BUMPS TO THIS POST.

Any advice will be gratefully accepted!

Adam Welz, Cape Town, South Africa

I have just heard from a couple of top Corydoras experts that this problem in my fish is due to too-high protein content of the food that I am giving them, causing "fatbubbles" under the skin. This will kill them.

Has anyone on this forum also experienced this?

Best,

Adam Welz