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INTRODUCTION
Many parasites are serious pathogens in intensive aquaculture in Japan (Ogawa and Yokoyama, 1998). One such parasite, Neobenedenia girellae , a capsalid monogenean, is problematic because it can cause high mortality in host fishes (Ogawa et al. 1995) and it has broad host specificity (Bondad-Reantaso et al. 1995). Some commercially important cultured fishes, such as the amberjack Seriola dumerili and the yellowtail S. quinqueradiata (Carangidae), the Japanese flounder Paralichthys olivaceus (Paralichthyidae) and the spotted halibut Verasper variegatus (Pleuronectidae), become infected with this monogenean (Ogawa and Yokoyama, 1998; Hirazawa et al. 2004). However, among these host fish species, S. dumerili is most susceptible to N. girellae (Hirazawa et al. 2004; Ohno et al. 2008).
Bondad-Reantaso et al. (1995) described the life cycle of this parasite. At a water temperature of 25°C, free-swimming oncomiracidia (body length: ~200 [mu]m) hatch from eggs after 4 days, attach predominantly to the fins and then migrate from the fins to the skin surface as they grow. The maturation of N. girellae (body length: ~2·1 mm) takes 10 days from larval attachment to the host. Active feeding by large populations of capsalid monogeneans on mucus and epithelial cells of the host fish can cause haemorrhage, inflammation and mucus hyperproduction (Paperna, 1991). Heavily infected fish may stop feeding, their body colour darkens, and they swim erratically and rub against the net, which may result in dermal ulceration and subsequent bacterial invasion (Woo et al. 2002).
Lipids play a vital role in long-term survival and in the completion of the life cycle of endoparasitic parasites (Furlong, 1991; Sherman, 1998). Parasitic protozoa require an exogenous source of essential lipids for growth, differentiation and life-cycle completion (Soudant and Chu, 2001). Utilization of fatty acids in serum is thought to be necessary for survival of the protozoan Plasmodium falciparum in erythrocytes. Characterization of the parasite fatty acid metabolism was important for developing a new strategy for controlling malaria (Mi-ichi et al. 2006). However, lipid content and fatty acid composition of N. girellae have not been investigated. Information regarding the lipid content and fatty acid composition of N. girellae would help to control this parasite.
In this study, the lipid content and fatty acid composition of adult N. girellae was investigated. We also investigated whether the...