What is Ich? (Cryptocaryon)
Cryptocaryon is a fully ciliated protozoan that is present in all saltwater environments, and is particularly prevalent in marine aquariums, aquaculture ponds, and in import and wholesale holding environments. The protozoan is considered an external parasite and is so widespread that many fish that enter the home aquarium market have had a good chance of being exposed to it at some point in their handling. The protozoan penetrates the skin and gills of the fish, and depending on the immune status of the fish, can cause symptoms as mild as just a few small white spots to more severe symptoms including severe irritation, loss of appetite, lethargy, severe respiratory distress, and death.
Why/How do fish get Ich?
Cryptocaryon is a parasite, and like most parasites it is very prevalent in the environment of the species it normally infects. Therefore, most wild fish are exposed to low levels of this parasite fairly frequently and are able to effectively fight off the infection without becoming seriously ill. What happens in an aquarium fish, however, is very different than what happens in a wild fish. In the wild, the number of free-floating Cryptocaryon per 100 gallons of water is extremely small. Whereas in a home aquarium with a relatively small volume of water and a concentrated population of fish, the number of Cryptocaryon has the opportunity to explode into a number hundreds of times higher than what would ever be experienced in the wild. The other thing that happens in a home aquarium is that the level of stress has the potential to be much more severe than what is found in the wild.
Almost all marine aquarium fish are wild harvested, and in a period of several days their lives change dramatically. They go from living on the reef to being collected, handled, shipped, and re-handled repeatedly. When those fish finally enter the home aquarium, they are then subject to yet another change in water parameters, diet, temperature, and environment and may even be subject to aggression from existing tank mates. To say the least, these fish are severely stressed to the point that their immune system may not be functioning properly, making them very susceptible to infections and parasites like Cryptocaryon. In an existing tank in which the fish are healthy, the introduction of a new fish or a decrease in water quality or temperature fluctuations may stress the fish to the point that the Cryptocaryon protozoans that were present but not creating problems will then rapidly cause a more serious infection.
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