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Nodular Disease
Symptoms:
Symptoms include smooth, yellowish-white lumps or boils (cysts) anywhere on the fish's body. The size of cysts vary from a few millimeters to a centimeter and are usually spherical or oval although some may be elongated or irregularly shaped. Nodular disease is generally confined to Carp but can affect a variety of aquarium fish, particularly Cichlids.
Cause:
Microsporidian and myxosporidian parasites such as Ichthyosporidium, Nosema, Myxobolus, and Henneguya and also the fungus Dermocystidium. These single-celled spores can multiply and spread rapidly. Their life cycle begins in the intestinal tract of a fish following ingestion. Here the spores enter the bloodstream, penetrating internal organs before forming visible cysts and boils on the fish's body. When these cysts rupture, millions of spores are released, perpetuating the cycle.
Treatment:
Unfortunately, no effective medication or chemical remedy is currently recognized. Disinfect any tanks and all equipment that have contained infected fish.