The teleost mucosal immune response at the host-parasite interface of tilapia, Oreochromis mossambicus, against Neobenedenia melleni

Neobenedenia melleni, a monogenean helminth of marine fishes, is a notorious parasite in aquaculture and public aquaria due to its short, direct lifecycle, high fecundity, low host specificity and often high pathogenicity. Immunity after exposure to live parasites is well documented but mechanisms are unclear. In the last decade, Hawaii has led the nation in mariculture of finfish but has experienced challenges due to N. melleni. Although a worldwide pathogen, the wild hosts of N. melleni are still unclear. The primary objectives of this dissertation were to investigate the mucosal immune response against N. melleni using Mozambique tilapia and to identify wild hosts in Hawaiian waters. In the present study, continuous exposure to N. melleni induced solid immunity associated with increased anti-parasite mucus and serum antibodies. Histopathologic evaluation of fish during development of immunity showed that fish with the lowest levels of infection displayed a tissue pattern of markedly increased eosinophilic cells, moderately increased mucus cells, and moderate levels of inflammation in the epithelium. Surveys of wild fishes identified several hosts of N. melleni and revealed similar parasites closely related to other capsalid parasites. To our knowledge, these are the first reports of protective antibodies against N. melleni , the association of eosinophilic cells at the host-parasite interface, and the analysis of wild capsalid hosts in Hawaii via molecular techniques. These findings may equip stakeholders with more comprehensive risk assessment tools and prevention strategies for mariculture and for the protection of wild fisheries.