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One of my aquarium fish (Uaru Amphicatoides) is sick. Two visible symptoms are a lot of mucus on the skin and heavy breathing. I have been searching the internet and the symptoms are consistent with a chilodonella (a ciliate) infection. I took some of the mucus (floating in the water) and inspected it under my microscope. I found some ciliates that might be chilodonella, but I am not sure abouit that. I made a small video, to be seen here . I hope someone recognizes this ciliate.

It is a ciliate, but clearly not Chilodonella. It looks a lot like Tetrahymena, actually. I had to rewatch the video on a better monitor to see it, but the mouth is visible from around the 8 second mark, and is consistent with a hymenostome, and in the right location for Tetrahymena. The shape and movement are quite reminiscent of histophagous free-living members of the genus I've seen.

I can't say if this is the infective organism, because I don't know anything about fish pathology. For what it's worth, a quick search shows that species of Tetrahymena do parasitize fish: https://www.sciencedirect.com/topics/bi ... etrahymena

Thank you for your answer. Interesting literature.