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''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 protozoan ''Ichthyopthirius''. Ich is one of the most common and persistent diseases in fish. 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 encysted parasite.〔 It is easily introduced into a fish pond 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. Whitespot is very damaging to the gills and skin. In heavily infected fish it can cause a rapid deterioration of condition, considerable distress and death. Infected fish have small white spots on the skin and gills (Fig. 2 and Fig. 3) and produce excess mucus, due to irritation. Whitespot causes most damage when entering and leaving the tissues of the fish. This can lead to the loss of skin and ulcers. These wounds can harm the ability of a fish to control the movement of water into its body. Damage caused to the gill tissue of an infected fish can also reduce respiratory efficiency. This means it is more difficult for the fish to obtain oxygen from the water, and becomes less tolerant to low levels of dissolved oxygen.〔()〕 ==Life stages== File:Life cycle of Ichthyophthirius multifiliis.jpg| The ich protozoan goes through these 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 (tomont). The tomont adheres to plants, nets, gravel or other ornamental objects in the aquarium.〔 * The tomont divides up to 10 times by binary 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 to 8 weeks at . Marine ich is a similar disease caused by a different ciliate, '' Cryptocaryon irritans''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ichthyophthirius multifiliis」の詳細全文を読む スポンサード リンク
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