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.

They may also have ragged fins, cloudy eyes, pale gills, increased mucus production, or changes in skin color, and they may appear thin.

Behavioural changes may be observed, such as scratching, abnormal swimming, lethargy, hanging at the surface or bottom of the tank, or breathing rapidly as if in distress.

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.