I have been loosing fish recently which has left me very confused as they haven't really had any symptoms... well the last one did, and I was able to trace it to Hexamita. My question is, after reading about it, I don't see how the disease is contagious. I have read that the protozoa lives in most fish and only becomes a problem if the fish is afflicted somehow physically... All of my fish have been healthy for years and I haven't added anything to the system at all. I dont know why this happened now. Now that I know what it is, I am going to start treating with metronidazole to try and save my remaining fish which are still behaving fine, but I just dont understand why this became a problem now and how it started... is it conceivable that it came in on a frozen silverside??