Wild-caught marine fish from three sites were examined over a period of up to 13 mo for infections of the parasitic ciliate Cryptocaryon irritans. The study concentrated on two sparid fishes, Acanthopagrus australis and Gymnocranius audleyi. Results show that infections of C. irritans are common on wild fish, not rare as previously thought. The data suggest that C. irritans may exhibit a degree of host specificity in the wild, and also that its natural distribution can be extended into estuaries and seasonally into warm temperate waters.