Ick, which is short for Ichthyophthirius multifiliis, is an ectoparasite that affects freshwater fish. It can survive in water temperatures between 5 and 30 degrees Celsius and lives off the blood of its host. Generally, Ick can live without a host for up to four days outside of its natural habitat; however, it cannot reproduce or spread without one. The parasite will attach itself to any available host fish if given the chance, making it difficult to eradicate from a population once introduced. To prevent ick from spreading in your aquarium or pond environment, you should quarantine all new fish prior to introducing them into the tank and perform regular tank maintenance such as changing 20-30% of the water bi-weekly and cleaning filter media regularly.