This news is a few months old but I though everyone might find this new discovery interesting. It seems that Ichthyophthirius or Ich, as it is commonly known, has two new species of bacteria that appear to reside within the Ich organism itself.
If you are interested in accessing the original journal abstract or the article, Endosymbiotic Bacteria in the Parasitic Ciliate Ichthyophthirius multifiliis. Just click on the title. There are also some beautiful images in the paper.
Interesting stuff with implications for further characterizing the role these bacteria may play in fish infections and new approaches to treatment.