Diversity and host associations of parasitic isopods (Isopoda: Cymothoidae) from marine fishes of parangipettai and Nagapattinam, Southeast Coast of India.

A total of 15 species of parasitic isopods, belonging to six genera, were identified from the examined marine fishes. The species and their respective hosts included: Cymothoa eremita from Parastromateus niger; C. indica from Ambassis ambassis ; Joryma brachysoma from Ilisha melastoma; J. hilsae from Pellona ditchela; Mothocya plagulophora from Hemiramphus far; M. renardi from Strongylura leiura; M. collettei and M. karobran from Tylosurus crocodilus; Nerocila phaiopleura from Sardinella longiceps, Chirocentrus nudus and Rastrelliger kanagurta; N. sundaica from Sardinella fimbriata; N. sigani from Siganus canaliculatus ; N. loveni from Opisthopterus tardoore; Norileca indica from Selar crumenophthalmus; N. triangulata from R. kanagurta; and Ryukyua circularis from Amblygaster sirm. The analysis revealed that although most parasitic isopods are not strictly host-specific, they display a distinct site specificity. Infestations were localized to the gill chamber, buccal cavity, or body surface, depending on the parasite species. The pathological effects also varied according to the site of attachment: parasites on the body surface induced more severe external lesions, those in the gill chamber caused moderate damage affecting respiration, while infestations in the buccal cavity generally resulted in comparatively mild impacts.