Feeding mostly on the mucus and epithelial cells of the skins surface occasionally on blood it attaches to the host by means of a complex hook and anchor arrangement and it is this attachment which damages tissues and causes great irritation to the fish. The fish shows obvious signs of irritation and the damaged areas can develop into significant skin ulcers and fin erosions, often with secondary bacterial and fungal infections. Gyrodactylus is frequently found as a mixed parasitic infestation along with parasitic protozoans such as Trichodina which also contribute to the irritation and the damage.

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