Shading Reduces Neobenedenia girellae Infection on Cultured Greater Amberjack Seriola dumerili

Juvenile greater amberjack were placed in a small cage and exposed to Neobenedenia girellae oncomiracidia for 48 h at an amberjack culture site under natural light or with a shade. The shading reduced worm intensity on the skin of fish by about 70%. Additional laboratory experimental infection comparing the larval infectivity under dark and light conditions revealed that the oncomiracidia were capable of infecting fish in complete darkness. These results suggest that the low infection rate in the shaded water is probably due to accumulation of the oncomiracidia into the bright area, resulting in the lowered density under the shade.