Diseases in fish are an important issue throughout the world, especially where fishing and aquaculture are better developed (Fonseca, 2003), because they may cause the loss of natural stocks. According to this, parasitism in fish has been frequently assumed to be an indicator of environmental health, and therefore, an essential complement for the development of aquaculture and the environmental balance in marine ecosystems. A number of parasites use a complex interaction web within their hosts’ ecological chains and in that context are vulnerable to any alteration or disturbance noticed on their habitat, even before higher taxa can be affected.
The presence of these ectoparasites may affect these body parts, causing gill filament atrophy, removal of brachial arcs, and obstruction of the mouth cavity and thus destruction of the tongue, compromising the whole of the fish behavior and leading, sometimes, to the death of the animal (Chavez- Lopez et al., 2005; Rhode, 2005).
The effects of the cymothoid infection vary according to the combination of the host-parasite status and balance on the host–parasite relationships, where they can cause lesions ranging from low impact up to irreversible difficult situations resulting sometimes in the host’s death, with regard to the injurious effects on host species. These effects include: behavioral changes; tissue damage; decrease in mean weight, size and growth; and in some cases, death (Brusca 1978, 1981; Romestand and Trilles, 1979; Leonardos and Trilles, 2003). In contrast, other studies concluded that infected fish were not significantly less healthy than non-infected ones (Bello et al., 1997; Colorni et al., 1997). Similarly Weinstein and Heck (1977) suggested that host damage, if any, due to cymothoid infection is minimal.
The Indian cymothoid fauna is relatively poorly known on marine fishes from the Indian coasts (Pillai, 1954, 1964; Ravichandran et al., 2010; Rameshkumar et al., 2011). The infection of isopod parasites in fishes is scanty and no such studies have been made in India. Hence, the present attempt will make to study the diseases of parasitic isopod infection in the fish on the of Tamil Nadu coast within an area of high ecological and commercial importance for the local fish industry.