From: http://dspace.stir.ac.uk/bitstream/1893/10147/1/Picon%20Camacho%20et%20al%20Parasitology%20Ich%20chemo%20review.pdfIt has a direct life cycle, which is temperature dependent such that the warmer the water temperature the faster the life cycle completes. The life cycle involves 4 diﬀerent stages: (1) the trophont, which resides within the surface epithelium of gills, ﬁns and other body surfaces; (2) the protomont, a free-swimming stage that exits the ﬁsh and settles on the substrate to become the encysted tomocyst stage (3) which in turn repeatedly divides by binary ﬁssion to produce tomites which are released to the water column. Tomites diﬀerentiate into the infective stage (4) the theront, which needs to ﬁnd a host within a short window to successfully complete the life cycle by penetrating the epidermis and developing into the trophont stage before it dies (Lom and Dyková, 1992; Matthews, 2005). Theronts can survive for up to 92 h at low water temperatures; their survival being inversely proportional to the ambient water temperature (Wagner, 1960; Aihua and Buchmann, 2001).
On farms, the most common approaches to treat this ciliate is through the use of either short (e.g. 30 min–4 h in tanks, raceways and ﬂow-through systems) or long (e.g. 7–15 days in pond culture) duration in-bath treatments which target the free-swimming stages of the parasite (i.e. protomonts and theronts). Of the other two stages, the trophont is protected lying underneath the host surface epithelium (Post and Vesely, 1983) whilst the tomocyst is protected by a resistant coat (Ewing et al. 1983) and as such, are rarely susceptible to