Cryptocaryon irritans
Yellow tang with white spots characteristic of marine ich
Scientific classification
Domain:	Eukaryota
(unranked):	SAR
(unranked):	Alveolata
Phylum:	Ciliophora
Class:	Prostomatea
Genus:	Cryptocaryon
Species:	C. irritans
Binomial name
Cryptocaryon irritans

Cryptocaryon irritans is a species of ciliates that parasitizes marine fish, causing marine white spot disease or marine ich (pronounced ick).^[1][2] It is one of the most common causes of disease in marine aquaria.

Cryptocaryon irritans was originally classified as Ichthyophthirius marinus, but it is not closely related to the other species. It belongs to the class Prostomatea, but beyond that its placement is still uncertain.

The symptoms and life-cycle are generally similar to those of Ichthyophthirius in freshwater fish, including white spots, on account of which Cryptocaryon is usually called marine ich. However, Cryptocaryon can spend a much longer time encysted. Fish that are infected with Cryptocaryon may have small white spots, nodules, or patches on their skin, fins, or gills. They may also have ragged fins, cloudy eyes, pale gills, increased mucus production, or changes in skin color, and they may appear thin. Behaviorally, fish may act different. They may scratch, swim abnormally, act lethargic, hang at the surface or on the bottom, or breathe more rapidly as if they are in distress.^[3]

Useful treatments (but not safe for reef tanks or invertebrates) of Cryptocaryon irritans are copper solutions, formalin solutions and quinine based drugs (such as chloroquine phosphate and quinine diphosphate).

Infections can be extremely difficult to treat because of the presence of other creatures in the tank, such as corals and other invertebrates, which will not survive standard treatments. Ideally fish with Cryptocaryon are quarantined in a hospital tank, where they can be treated with a copper salt or using hyposalinity, 1.009 specific gravity. The display tank needs to be kept clear of fish for 6–9 weeks, the longer the better. This gives time for the encysted tomonts to release infectious theronts, which die within 24–48 hours when they cannot find a host.

• Freshwater ich for the similar disease of freshwater fishes

• Colorni, Angelo (December 1987). "Biology of Cryptocaryon irritans and strategies for its control". Aquaculture. 67 (1/2): 236–237. Bibcode:1987Aquac..67..236C. doi:10.1016/0044-8486(87)90041-X.
• Dickerson, Harry W. (Summer 1994). "Treatment of Cryptocaryon irritans in Aquaria". SeaScope. 11.
• Diggles, B. K.; Lester, R. J. G. (June 1996). "Infections of Cryptocaryon irritans on wild fish from southeast Queensland, Australia". Diseases of Aquatic Organisms. 25 (3): 159–167. doi:10.3354/dao025159.
• Goto, Tsuyoshi; Hirazawa, Noritaka; Takaishi, Yoshihisa; Kashiwada, Yoshiki (16 September 2014). "Antiparasitic effects of Sophora flavescens root extracts on the ciliate, Cryptocaryon irritans". Aquaculture. 435: 173–177. doi:10.1016/j.aquaculture.2014.09.007.
• Li, Ruijun; Dan, Xueming; Li, Anxing (December 2013). "Siganus oramin recombinant L-amino acid oxidase is lethal to Cryptocaryon irritans". Fish & Shellfish Immunology. 35 (6): 1867–1873. Bibcode:2013FSI....35.1867L. doi:10.1016/j.fsi.2013.09.026. PMID 24113573.
• Lin, Qianqian; Yang, Mei; Huang, Zhen; Ni, Wei; Fu, Guoliang; Guo, Guowei; Wang, Zhengchao; Huang, Xiaohong (8 November 2013). "Cloning, expression and molecular characterization of a 14-3-3 gene from a parasitic ciliate, Cryptocaryon irritans". Veterinary Parasitology. 197 (3–4): 427–435. doi:10.1016/j.vetpar.2013.07.028. PMID 23932453.
• Yin, Fei; Gong, Qiyang; Li, Yanwei (February 2014). "Effects of Cryptocaryon irritans infection on the survival, feeding, respiratory rate and ionic regulation of the marbled rockfish Sebastiscus marmoratus". Parasitology. 141 (2): 279–286. doi:10.1017/S0031182013001613. PMID 24139291. S2CID 22057733.

• Cryptocaryon