I know this is an old post; I'm posting this in case anyone else comes across it with a similar issue. My Mandarin had this issue. It is captive bread and about 1.5" long. It was eating plenty of pellets, baby brine and pods in an established 60 gal tank with fuge, but breathing very hard. I treated it with Maracyn 2 and the heavy breathing stopped within the 6 day treatment window. It is now two weeks post treatment and still very active, but since the treatment has stopped eating. I'm hoping it comes around soon, but fairly pessimistic. Anyway, hope this helps someone!