Infections of Cryptocaryon irritans on wild fish from southeast Queensland, Australia

Wild-caught marine fish from 3 sites in SE Queensland, Australia, were examined over a period of up to 13 mo for infections of the parasitic ciliate Cryptocaryon irritans. Infections of C. irritans were found to be common on the fish sampled. Out of a total of 358 fish (14 species), 239 (66.7%) from 13 species were found to be infected. At Site 1 at the mouth of an estuary, the prevalence of C. irritans infections was 79% and the mean intensity was 12.9 parasites fish(-1). At Site 2, a coastal bar area, the prevalence of infection dropped to 66% and a mean intensity of 5.0 parasites fish(-1), whilst at Site 3 on the Great Barrier Reef, prevalence was lowest at 51% with a mean intensity of 2.3 parasites fish(-1). The study concentrated on 2 sparid fishes, Acanthopagrus australis from Sites 1 and 2 and Gymnocranius audleyi from Site 3. The prevalence of infections on A. australis from Site 1 (n = 101) was 100% with a mean intensity of 14.6 parasites fish(-1), whilst at Site 2 (n = 74) the prevalence was 88% at a mean intensity of 5.2 parasites fish(-1). There was no apparent seasonality in prevalence or intensity of infections al Sites 1 and 2 despite water temperatures ranging between 15 and 27 degrees C. At Site 3, the prevalence of infections of G. audleyi (n = 39) was 38% with a mean intensity of 1.9 parasites fish(-1). The diameter of the tomonts collected from A. australis from Sites 1 and 2 varied inversely with water temperature, and was not related to host size. Our results show that infections of C. irritans are common on wild fish, not rare as previously thought. This may be partially due to the increased sensitivity of our tomont collection technique. Our 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.