Temporal Change in the Swimming Ability and Infectivity of the Oncomiracidium of a Monogenean <i>Neobenedenia girellae</i>

Abstract

In this study, we assessed the influence of different water temperatures on the swimming ability of the oncomiracidium of Neobenedenia girellae. In addition, we investigated the temporal change in their infectivity to Seriola dumerili after hatching at 25°C. Most oncomiracidia in the cell culture flask filled with seawater deciliated and predominantly crept on the bottom by the end of 6 h experiment. Approximately 9% of the oncomiracidia in seawater-containing wells of a 12-well cell culture plate were non-swimming and became trapped in the air-water surface interface. However, these effects were mitigated when a polyethylene sheet was placed on the seawater surface in the wells. When conducting the experiment using this method, the oncomiracidia remained active and were still swimming at 60, 72, and 108 h after hatching at 30°C, 25°C, and 20°C, respectively. The retention time of the oncomiracidia's swimming ability decreased as the water temperature increased. The oncomiracidial infectivity was reduced after 24-25.5 h or more after hatching. At 5 days after the exposure to S. dumerili, the number of attached N. girellae was significantly lower, and their body length was significantly shorter when using oncomiracidia that were 36-37.5 h after hatching compared to freshly hatched ones.