Marine white spot (ick) (<i>Cryptocaryon irritans</i>)


Fish constantly rubs or scratches itself against any object available.
White raised spots (1-2mm)
White raised spots of 1-2mm are apparent all over body and fins.
Dust-like spots all over fish
Body and fins are covered with dust-like very small spots. Fish looks as if it is covered in pepper.
Small dust-like gold-grey spots
The body is covered with a very fine dust-like spots of a gold-grey colour.
Haemorrhages - skin
Bloody haemorrhages are apparent over several parts of the skin.
Large white spots on Skin
Skin is dotted with large (1-2mm) white hazy spots.
Spasms - convulsions
Fish appears to be having a fit, jerking and twisting abnormally.
Abnormal swimming - streaks
Fish swims in short bursts, then stops.
Faded colours
Colours of fish look washed out compared to normal.
Hanging at surface
Fish stays at water surface all the time.
Red necrotic lesions - skin
The skin shows red necrotic lesions.
Reluctant to feed
Fish comes to eat but with evident lack of appetite.
Fish appears to have lost all control of its bodily movements, it jerks.
A typical symptom of Crytobia is blindness, most noticeably fish swimming into objects.
Corneal opacity
Cornea of eye becomes totally opaque.
Laying on side
Fish lies on side, usually motionless.
Listless and lethargic
Fish moves very lazily in water, much less than normal, lacks interest.
Pale slime film over skin
A slimy thin grey/white film covers the body.
Restless swimming
Fish continue in non-stop swimming without any rests.
Sits on bottom
Fish sits still in upright position, on the bottom of tank or pond.
Skin excessive sliminess
Skin shows mucous and slime far in excess of normal.
Sluggish movements
Fish moves almost reluctantly in the water.
Whirling or tumbling
Fish fall down in a spiral or "head-over-heels" fashion.
Vertical swimming head up
Fish swims in an almost vertical position with its head upwards.
Salinity full salt water
Normal full salinity salt water.


Protozoan ciliate. Very contagious, infects most species of marine fish. Parasite can remain dormant for long periods of time subeptitelially, often breaking out into the reproductive phase only when fish are stressed.


Disease is seldom fatal quickly, giving time for diagnosis and successful treatment. In dormant stage causes no problems. Possibly many fish carry the parasites, without notice or harm.


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In hatcheries & closed systems use regular quarantine procedures to prevent outbreaks. In Aquaculture in sea cages try to site cages in waters where the parasite is not prevalent.

DNA and RNA diagnostic references

Taxonomic affinities of Cryptocaryon irritans and Ichthyophthirius multifiliis 
inferred from ribosomal RNA sequence data 

From Diseases of Aquatic Organisms Volume 22: 39-43, 1995

B. K. Diggles, R. D. Adlard Department of Parasitology. The University of Queensland 
Brisbane, Queensland 4072. Australia


Dr. Burgess, Peter
Aquarium Sciences & Conservation
Brentwood Essex  UK


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