Genus Costia is a single-celled protozoan that belongs to the Cryptobia family. It is commonly found in freshwater environments such as fish ponds and aquariums. When searching for information on this microorganism, it may also be referred to as Ichthyobodo necator or Cryptobia costata. These are synonyms for Genus Costia and indicate the same type of microbe. While Genus Costia is not harmful to humans, it can cause a range of health problems for fish. Symptoms include lethargy, loss of appetite, and skin irritation. It is crucial to identify and treat a Genus Costia infection quickly to prevent further harm to the fish and to maintain a healthy aquatic environment.