A checklist of the parasitic Cymothoidae of Indian fishes was compiled from parasitological records published between 1783 and 2011. The checklist is arranged alphabetically, providing valid names, synonyms and authorities of the parasite species, as well as valid names and synonyms of the host fish, its capture sites, author(s) and date of published records. The host list consists of all parasites species listed under the host species. A total of 47 nominal species corresponding to 36 valid species are listed from 74 host species belonging to 34 families. Several parasites not identified to species level and parasite species without the host data or where the parasite was found not associated with a fish are also included in this checklist.

Until now, 36 species belonging to the family Cymothoidae (Crustacea, Isopoda) were recorded from Indian fishes. In this study, ten additional cymothoids are reported in India, most of them for the first time. They parasitize nine fish species, several of them being new host species.

Eleven Nerocila species are recorded from 22 marine fishes belonging to 15 families. Three, Nerocila arres, Nerocila depressa, and Nerocila loveni, are new for the Indian fauna. N. arres and Nerocila sigani, previously synonymized, are redescribed and their individuality is restored. Nerocila exocoeti, until now inadequately identified, is described and distinctly characterized. A neotype is designated. New hosts were identified for N. depressa, N. loveni, Nerocila phaiopleura, Nerocila serra, and Nerocila sundaica. Host–parasite relationships were considered. The parasitologic indexes were calculated. The site of attachment of the parasites on their hosts was also observed. A checklist of the nominal Nerocila species until now reported from Indian marine fishes was compiled.Electronic supplementary materialThe online version of this article (doi:10.1007/s00436-012-3263-5) contains supplementary material, which is available to authorized users.

The parasitic isopod family Cymothoidae Leach, 1818 of the India exclusive economic zone is reviewed. A total of 56 nominal species corresponding to 48 valid species belonging to sixteen genera are reviewed from 73 host species belonging to 35 families. Mothocya plagulophora (Haller, 1880), Nerocila depressa Milne Edwards, 1840, Nerocila loveni Bovallius, 1887, Nerocila trichiura (Miers, 1877), Norileca triangulata (Richardson, 1910) and Ryukyua globosa Williams & Bunkley-Williams, 1994 are redescribed. Indusa pustulosa Pillai, 1954 is synonymised with Agarna malayi Tiwari, 1952; Cymothoa krishnai Jayadev Babu & Sanjeeva Raj, 1984 is synonymised with Cymothoa eremita (Brünnich, 1783) and Nerocila priacanthusi Kumari, Rao & Shyamasundari, 1987 is synonymised with Nerocila arres Bowman & Tareen, 1983. Ourozeuktes bopyroides (Lesueur, 1814) is revised and excluded from the Indian fauna. The Indian cymothoid species Agarna bengalensis Kumari, Rao & Shaymasundari, 1990, Cymothoa asymmetrica Pillai, 1954 and Nerocila hemirhamphusi Shyamasundari, Rao & Kumari, 1990 are regarded here as species inquirenda. A key to the Indian genera of the family Cymothoidae and keys to the Indian species of the genera Cymothoa, Joryma, Mothocya, and Nerocila are presented. A checklist of the valid Cymothoidae species until now reported from Indian marine fishes are compiled. Host preferences, morphological variability and distribution are discussed.

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Crustaceans are found in every type of aquatic ecosystem, and there are species adapted to extremes of temperature, pressure, salinity, and even anoxia. Parasitic isopods are typically marine and usually inhabit the warmer seas. They are blood-feeding; several species settle in the buccal cavity of fish, others live in the gill chamber or on the body surface including the fins. Isopods can cause morbidity and mortality in captive fish populations. The damage of gill filaments thus was not only due to the feeding but also by the pressure exerted by the dorsal side of the parasite. Erosion of gill lamellae, damage of gill rakers and pale gills were the severe gross lesions observed as a consequence of isopod infestation. Infested fish exhibited histopathological anomalies such as tissue reactions, primarily associated with the formation of granulomas consisted of macrophages and epithelioid cells, which are occasionally surrounded by a thin rim of fibroblasts. A marked increase in the size of the parasite is associated with the development of marsupium full of juvenile parasite. The infestation usually pressure atrophy often accompanies the presence of larger parasites. They may lead to economic losses in commercial species of fish. Thus, treating fishes infected with isopods without treating their environment may only provide temporary relief. It is also important to recognize the potential for secondary infections associated with severe isopod infections.

Four cymothoid isopods, parasites of fishes, are reported from India. Two new species, Nerocila poruvae and Joryma hilsae are described. A full description of Nerocila longispina Miers, 1880 is included and two hosts are identified. The distribution and hosts of Anilocra dimidiata Bleeker, 1857 are updated. Nerocila poruvae, N. longispina and Anilocra dimidiata were collected from the Southeastern coasts of India and Joryma hilsae from the Southwestern coasts.

Two parasitic cymothoidae (Crustacea, Isopoda) are reported parasitizing fishes Hemiramphidae in India. Ceratothoa angulata, found in the buccal cavity of its host, is reported for the first time from India. Mothocya plagulophora, a branchial species, already known from the Southwest coast, is now recorded from the Southeast coast of India. Host-parasite relationships are considered.