page_title: Ichthyophthirius multifiliis
section_title: Clinical signs
hierarchical_section_title: Ichthyophthirius multifiliis / Pathology and clinical signs / Clinical signs
caption_attribution_description: English: Trophonts of Ichthyophthirius multifiliis (diameter 300 μm) in the epidermis of a rainbow trout tail fin (light microscopy with subillumination). The horseshoe-shaped macronucleus is visible. (photo: Kurt Buchman, University of Copenhagen)
context_page_description: Ichthyophthirius multifiliis, often termed "ICH", is a parasitic ciliate described by the French parasitologist Fouquet in 1876. Only one species is found in the genus which also gave name to the family. The name literally translates as "the fish louse with many children". The parasite can infect most freshwater fish species and, in contrast to many other parasites, shows very low host specificity. It penetrates gill epithelia, skin and fins of the fish host and resides as a feeding stage inside the epidermis. It is visible as a white spot on the surface of the fish but, due to its internal microhabitat, it is a true endoparasite and not an ectoparasite.
  It causes a disease commonly referred to as white spot disease due to the macroscopically visible trophonts in the skin and fins. The trophont, continuously rotating, is surrounded by host cells, producing a minute elevation of the skin. These light-reflecting nodules are recognized as white spots.
  If strict bio-security rules are violated, the parasite may be introduced into a fish rearing unit by transfer of fish or equipment from infected systems.
context_section_description: Typical behaviour of clinically infected fish includes:
  ·       Anorexia (loss of appetite)
  ·       Increased breathing rate (hyperventilation)
  ·       Discoloration
  ·       Abnormal behaviour (inactivity, isolation)
  ·       Resting on the bottom
  ·       Flashing (rubbing and scratching against objects)
  ·       Balance disturbance. Upside-down swimming near the surface.
  Theront penetration may elicit erratic swimming and movements reflecting irritation of fish surfaces. The trophont is not visible to the naked eye until it has fed on the fish and grown to a diameter of about 0.3-0.5 millimetres. The white spots may reach more than 1 mm in diameter and are easily recognized on skin and fins whereas trophonts attached to the gills are hard to see due to the gill cover (operculum).
  Skin: ICH infections are usually visible as one or several characteristic white spots on the body or fins of the fish. The white spots are single cells called trophonts, which feed on host cells (epidermal cells and leukocytes attracted to the site) and may grow to 1 mm in diameter. Heavy infections with subsequent lesions following trophont escape leave the skin irregular, fluffy and greyish.
  Gills: Gill infection may cause breathing at the surface and increased ventilation movements of operculae.
caption: Trophonts of Ichthyophthirius multifiliis (diameter 300 μm) in the epidermis of a rainbow trout tail fin (light microscopy with subillumination). The horseshoe-shaped macronucleus is visible. (photo: Kurt Buchman, University of Copenhagen)
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