Diurnal pattern of skin fluke infection in cultured amberjack, Seriola dumerili, at different water depths

• Neobenedenia girellae infection predominantly occurred during the day at the surface.
• Infection was significantly reduced when fish were at 2 and 4 m below the surface.
• Water current play important role in infection in the fish farm.
• Results suggest N. girellae infection can be reduced by modifying culturing methods.

Skin fluke infection is a major parasitic problem in the aquaculture industry. Present control measures such as bath treatments are effective for removing flukes from fish but require extensive labour and time. Moreover, bath treatments cause great stress to the fish, and occasionally lead to post-treatment mortality. Our ultimate goal is to develop a culture technique that prevents or lowers the chance of fish encountering larval skin flukes, thus reducing infection. However, little is known about when and where these infections occur on fish farms. We conducted a field experiment at a culture site to determine the diurnal pattern of skin fluke infection at different water depths. Juvenile amberjack, Seriola dumerili, were placed in enclosed mesh cages and exposed to skin flukes at depths of 0, 2 or 4 m for 4 h during different times of the day. A Neobenedenia girellae infection occurred predominantly at the surface during the mid-day. The infection rate declined considerably during the night. The parasite burden was significantly decreased with water depth, and up to an 80% and 95% reduction in intensities was observed when fish were exposed at a depth of 2 and 4 m, respectively. These results suggest that skin fluke infection can be significantly reduced by systematic management strategy and modification of culture techniques.