Abstract: Monogeneans are ubiquitous, less understood parasite in context of aquaculture practices which generate a potentially stressful environment to the cultured animals, with the possible suppression of the immune system, rendering the fish more susceptible to different infectious diseases. Among the different parasites, monogenean ectoparasites are known to parasitize a large number of fish. Fish hosts susceptible to a certain parasite show an ability to mount a protective response after infection. The innate host factors like complement, lectins, acute phase reactants, macrophages are reported to bind monogeneans and elicit severe damage to the parasites by targeting the monogenean tegument, gastro-dermis and glands. Increase in the hostís production of adaptive and non-adaptive factors following monogenean infections of certain duration explains the acquired response. However, clever skill of the monogenean to avoid and even exploit the wide array of immunological elements of the host poses an interesting event in the dynamic interactions between host and monogenean. Understanding of diverse monogenean morphology in context of its life-cycle and host interaction may give clue to avoid negative impact of this parasite.

Keywords: Monogenean, Aquaculture, Morphology, Immune response