Ich parasite

By: Peyton whisnant

About Ich

Ichthyophthirius multifiliis (commonly known as freshwater white spot disease, freshwater ich, or freshwater ick) is a common disease of freshwater fish. It is caused by the protozaIchtyopthirius. Ich is one of the most common and persistent diseases. The protozoan is an ectoparasite. White nodules that look like white grains of salt or sugar of up to 1 mm appear on the body, fins and gills. Each white spot is an ensysted parasite. It is easily introduced into a fish pond tank, or home aquarium by new fish or equipment which has been moved from one fish-holding unit to another. Once the organism gets into a large fish culture facility, it is difficult to control due to its fast reproductive cycle and its unique life stages. If not controlled, there is a 100% mortality rate of fish. With careful treatment, the disease can be controlled but the cost is high in terms of lost fish, labor, and cost of chemicals.

Where does it live?

The freshwater ich parasite thrives in uncleaned fresh water ponds or tanks, and they follow a strict five-day life cycle.

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Interesting facts

Multifiliis is one of the most prevalent protozoan parasites of fish and is an obligate parasite which means that the parasite cannot survive unless live fish are present. Adult organisms have an oval to round shape and measure 0.5 to 1.0 mm in size. The adult parasite is uniformly ciliated and contains a horseshoe-shaped nucleus which can be seen in older individuals. It is an important pathogen of ornamental and farm-raised food fish species when reared under intensive conditions. Wild fish populations are also susceptible and outbreaks are occasionally seen. There are few aquarists that have not met it on one or more occasions.

The ich protozoa goes though the following life stages

  • Feeding stage : The ich trophozoite (a protozoan in active stage of life) feeds in a nodule formed in the skin or gill epithelium.
  • After it feeds within the skin or gills, the trophozoite falls off and enters an encapsulated dividing stage (tormont). The tomont adheres to plants, nets, gravel or other ornamental objects in the aquarium.
  • The tomont divides up to 10 times by bionary fission, producing infective theronts, thus dividing rapidly and attacking the fish.

This life cycle is highly dependent on water temperature, and the entire life cycle takes from approximately 7 days at 25 °C (77 °F) to 8 weeks at 6 °C (43 °F).

Marine ich is a similar disease caused by a different ciliate, Cryptocaryon irritants.