Effectiveness of chemotherapeutants against scuticociliate Philasterides dicentrarchi, a parasite of olive flounder.

The histophagous scuticociliate Philasterides dicentrarchi causes fatal scuticociliatosis in farmed olive flounder Paralichthys olivaceus. The average monthly prevalence of scuticociliatosis with P. dicentrarchi infections was very high from May to July (40+/-3 to 79+/-2%) in olive flounder at farms of Jeju Island, South Korea, from 2000 to 2004. The prevalence of mixed infection along with Vibrio spp. infection was higher (49+/-8%) than that of scuticociliatosis alone. To date no effective control measure for P. dicentrarchi infection has been described and large economic losses continue. In the present study 3 chemotheraputants (formalin, hydrogen peroxide and Jenoclean) were used. Among these, bath treatment with Jenoclean at a low concentration of 50ppm proved effective; the results were confirmed with in vitro motility assessments and morphological changes in P. dicentrarchi. A similar trend was noted following hydrogen peroxide treatment. However, formalin was only moderately effective at this concentration. Therefore, hydrogen peroxide and Jenoclean are the promising compounds effective at low concentrations with short application time.