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Affected fish

All fish may be infected although Anabantoids (Gouramies and Siamese Fighters), Swordtails and Platies are particularly prone.


The Costia parasite is commonly found on the skin of aquarium fish and is normal at low levels. The parasite can leave the host fish and transfer to another with relative ease, although it can only survive without a host for a few hours. The parasite is only a problem when it is allowed to multiply rapidly as a result of a reduced immune system.


Typically, fish will display signs of irritation such as flicking or scratching against objects, lack of movement, clamped fins, and swimming on the spot (Shimmying) An increase in mucus production, reddening of skin patches and difficulty breathing are also common side effects.


Good general conditions will prevent most outbreaks, although new fish, or those under stress may succumb. Quarantining of new fish prone to the disease may help prevent any outbreaks in the main aquarium.


Most general protozoan (small parasite) treatments will be effective if the outbreak is caught early enough. If the fish affected can tolerate warmer temperatures, raising the temperature will also help. Isolating affected fish in a separate treatment tank will also help to prevent spreading.

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