Branchial cymothoids infesting the marine food fishes of Malabar coast

Occurrence of cymothoid isopods parasitizing the branchial chamber of marine food fishes along the Malabar coast was investigated. Live and fresh fishes collected from the Ayyikkara fish landing center (Lat. 11°51′N, Long. 75°22′E; Malabar coast, India) were subjected to the thorough observation for the presence of branchial cymothoids for 3 consecutive years (November 2009–November 2012). Among the recovered cymothoids, 11 species were branchial residents belonging to 6 genera; the species include Agarna malayi, Catoessa gruneri, C. boscii, Joryma hilsae, J. brachysoma, J. engraulidis, J. sawayah, Mothocya collettei, M. renardi, Norileca indica and Ryukyua circularis; highest prevalence being exhibited by two species of Mothocya, (M. renardi and M. collettei) parasitizing the belonidaen fishes, Strongylura leiura (92.15 %) and Tylosurus crocodilus crocodilus (87.2 %) respectively. Except Mothocya species, which preferred the branchial floor for infestation, all recovered branchial cymothoids were found attached the inner wall of the operculum. In several instances, the parasites appeared in male–female pairs, one in each branchial cavity. Ovigerous female members of all species of branchial cymothoids except R. circularis showed remarkable bending either towards left or right depending on whether they are located in right or left branchial cavity of their respective host fishes. The deleterious effects of parasitization by all recovered branchial cymothoids include the formation of a pit like depression in the branchial chamber and atrophy of the gill filament; the damage was more pronounced in the gill cavity of parasitized host fishes where the ovigerous female member was accommodated.