Ichthyophthirius
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{{Taxobox | color = khaki | name = Ichthyophthirius | regnum = Protista | phylum = Ciliophora | classis = Oligohymenophorea | ordo = Hymenostomatida | familia = Ichthyophthiriidae | genus = Ichthyophthirius }} Ichthyopthirius multifiliis is a species of ciliate protozoa which parasitizes freshwater fish. The disease it causes is usually called Ich or white spot, and becomes especially serious in enclosed areas, where it spreads quickly from one fish to another. Ich is the disease responsible for the most fatalities in aquarium fish and can cause notable damage to aquaculture.
Ich infections are usually visible in the form of white spots on the side of the fish. The fish may also show behaviours such as flashing, or rubbing up against objects. The white spots, which are pockets of fish epithelium, contain parasitizing Ichthyophthirius cells, called trophonts, which feed on the tissues of the host and may grow to 1 mm in diameter. After approximately one week of parasitism, mature trophonts leave their host, settle to a substrate and secrete a cyst. Called a tomont, this incysted form then undergoes rapid division over approximately twenty-four hours, producing six hundred to one thousand daughter cells, known as tomites. Once the tomites reach maturity, they exit the cyst and differentiate into their theront stage. Theronts then infect succeptable freshwater fish, beginning the cycle anew. The entire life-cycle takes about seven to ten days to complete.
Treatment
If ich is detected before it becomes too serious, a number of different treatments can be applied. The most recommended method of treatment for ich consists of adding aquarium salt. The salt is to be added gradually until a specific gravity of 1.002 is achieved. This is done because ich is highly intolerant of salt whereas freshwater fish can tolerate small amounts. Also water temperature is to be raised gradually to 82-86F. This reduces the life cycle of the parasite. Other treatments include formalin and malechite green. All target the free-living theronts and tomonts, which only survive about three days in absence of a host fish.
A similar disease in saltwater fish, sometimes called marine ich, is caused by the ciliate Cryptocaryon. Originally this was considered another species of Icthyophthirius, called I. marinus, but it belongs among a completely different group of ciliates. Ichthyophthirius is a hymenostome, now usually given its own family.