Effects of temperature and host species on the life cycle of Cryptocaryon irritans

Cryptocaryon irritans, an important protozoan ciliate, infects almost all species of marine teleosts and causes heavy economic losses in aquaculture. In industrial aquaculture, culture container rotation is an effective method to control cryptocaryoniasis. However, the accurate frequency and times of container rotation for different temperatures or fish species has not been reported but is very important information for the application of the method. In the present study, we investigated the duration of C. irritans trophont residence and theront production in three fish species at temperatures from 18 °C to 32 °C with 2 °C intervals. The results indicate that duration of trophont residence and theront excystment was shorter with rises in temperature, especially from 18 °C to 22 °C. In different fish species, the length of trophont residence varied whereas the length of theront excystment was very similar at the same temperature. In line with these data, we determined the frequency and times that tomonts were removed, and results demonstrated that all the tomonts can be completely removed with 2 or 3 days interval for 2 or 3 times (from 22 °C to 32 °C), and the removal of tomonts was identical in three fish species at the same temperature. At 18 °C and 20 °C, however, the interval of tomont removal was > 4 days. Lastly, we verified the removal of tomonts with Trachinotus ovatus as host at 22 °C and 30 °C by a placemat removal method. In conclusion, these data provide an important basis for defense against C. irritans infection by the interruption of its life cycle in an intensive aquaculture system.