Effect of Neobenedenia girellae (Monogenea) infection on host amberjack Seriola dumerili (Carangidae)

This study was designed to investigate: 1) the distribution of Neobenedenia girellae (Capsalidae) on host amberjack Seriola dumerili (Carangidae) and growth of the parasite during infection; 2) the influence of different N. girellae exposure levels on S. dumerili growth; and 3) the histopathological skin changes of S. dumerili infected with N. girellae at the different parasite densities. N. girellae were mostly found on pelvic and pectoral fins of S. dumerili at 1 and 3 days after exposure of S. dumerili to N. girellae oncomiracidia. The parasites were primarily found on the skin surface at 6 days after exposure, and all mature N. girellae specimens were found on the skin surface at 9 and 12 days after exposure. These results show that N. girellae migrated from the fins to the skin surface during parasite growth. The growth of S. dumerili infected with N. girellae was significantly slower compared with that of uninfected fish when the number of infected parasites was more than 0.285 ± 0.042/cm2 fish surface showing that N. girellae infections hindered the growth of the host fish. In addition, the feed conversion ratio was positively correlated with the number of infected parasites on fish. Furthermore, the thickness of S. dumerili epidermis with attached N. girellae was negatively correlated with both the N. girellae infection duration and the number of infected parasites. Thus, larger N. girellae caused more severe infections on host S. dumerili. These results in this study could be applied to control N. girellae infections and to promote stable S. dumerili production in aquaculture.