Predation of Cyclopoid Copepods on the Theronts of Ichthyophthirius multifiliis: Shedding Light on Biocontrol of White Spot Disease

White spot disease, caused by the parasitic ciliate Ichthyophthirius multifiliis, is a significant threat to the freshwater fish farming industry worldwide, resulting in massive mortality and economic losses. Eliminating the free-swimming theronts from the culture environment is considered crucial for the control of I. multifiliis infection. It is well-documented that planktonic ciliates are valuable food resources for macro-zooplankton in aquatic ecosystems. In this study, we developed a fluorescence labeling method for alive theronts and found that cyclopoid copepods Thermocyclops taihokuensis, Mesocyclops spp., Macrocyclops sp., and Paracyclopina sp. present predation on the theronts in co-culture experiments. Laboratory challenge tests further confirmed that the presence of zooplankton in the culture water body significantly reduced the infection of I. multifiliis in goldfish (p < 0.01). Results from this study revealed that cyclopoid copepods have the potential to be used as biological control agents against white spot disease in aquaculture.

Automated summary

White spot disease, caused by the parasitic ciliate Ichthyophthirius multifiliis, is a significant threat to the freshwater fish farming industry worldwide. The presence of zooplankton, specifically cyclopoid copepods, in the culture water body can significantly reduce the infection of I. multifiliis in goldfish. This study suggests that cyclopoid copepods have the potential to be used as biological control agents against white spot disease in aquaculture.