Identification Of Neobenedenia Melleni In Mariculture Zone At Xiangshan Bay And The Study On The Biological Characteristics Of N.melleni And Histopathology Of Its Infection Caused Disease In Host Eyes

The subfamily Benedeniinae were are the major parasites that caused serious harm to mariculture fishes at Xiangshan Bay and has caused a huge economic losses. In this study, we had identified the ectoparasite pathogen infected the major mariculture fish, and had studied the biological chiaracteristics of N.melleni and histopathology of its infection caused disease in host eyes. The researches could provide some theoretical basis for the prevention and treatment of Benedeniasis.In this paper, we had identified Benedeniinae ectoparasite infecting the surface of four important mariculture fishes (Pseudosciaena crocea, Miichthys miiuy, Lateolabrax japonicus, Pagrosomus majo) at Xiangshan Bay. It showed that the monogenean was morphologically similar to Neobenedenia melleni. The sequence analysis suggested that partial 28S rDNA from the monogenean and Neobenedenia were fundamentally identical, varying from 97.6% to 100% . The analysis of ITS1 sequence suggested that the monogenean had a hightest homology with Neobenedenia melleni gene sequence, reached 99.7%; and the homology of the monogenean and Neobenedenia girellae gene sequence was 99.4%. The results of two identification methods show that the benedeniinae on four important maricultured fishes in Xiangshan Zhejiang was Neobenedenia melleni.The morphology of N. melleni including adults, oncomiracidia and eggs were studied by Scanning electron microscopy (SEM). The body back surface of N. melleni adult was coverd with microvilli. The eggs had two slender antennaes instead of two recurved hooks. The accessory sclerites and anterior hamuli of oncomiracidia were in prototype and the morphology of posterior hamuli and hooklet of oncomiracidia were similar to that of the adult.We also studied the characteristics of oviposition of N. melleni. The results showed that the new eggs appeared immediately in the adult body after the mature egg excreted. And we found that the egg-laying rate of N. melleni increased when detached from their host. Free-swimining oncomiracidia hatched from eggs after 4-5 days at water temperature of 25℃, and the mode of hatching out was started with head of oncomiracidia. The oncomiracidia moved about immediately after hatching, they were susceptive to water currents and positive phototaxis.Effects of different salinities against N. melleni were examined in vitro and in vivo. In vitro we found that the body contraction phenomenon of N. melleni occurred thirty minates after exposure to 13 ppt salinity. In vivo we found that there were 95.2% N. melleni shedding from the surface of the host P.crocea after one-hour exposure to 7 ppt salinity and but it had no effect on the host during the entire experimental process.The histopathology of N. melleni-caused diseased in the eyes of P. crocea was studied. It showed that the parasites attached to the epithelium by the haptor, and epithelial cells of the cornea were often partially lost. There were massive inflammatory cells infiltrated in corneal stroma. The epithelium close to the anterir attachment organs and pharynx became thinner, so we inferred that the parasite feed on the epithelial cell by the pharynx.