The paper presents a first time report on the host specific parasitic occurrence of copepod, Caligus cybii, on the barred seer fish, Scomberomorus commerson distributed along the Malabar Coast, India. Of 81 fish species belonging to 35 families examined during the period from Jan 2012 to Jan 2014, only S. commerson was parasitised by C. cybii. 361 individual host fish examined, 80 were found to be infested (P= 22) with a total of 162 sexually dimorphic male and female of C. cybii (I= 2.02). Significantly, high degree of disproportion in the sex ratio of the recovered members of C. cybii was found existed inasmuch as more than 91% (148 out of 162) of them were reproductively active females. Invariably, all of them were found attached the inner epithelial lining of the operculum of the host signifying the strict site specific parasitisation. Light and scanning electron microscopic study showed the presence of structurally and functionally specialised mouthparts and appendages suited for their parasitic existence was evidenced by the present light and scanning electron microscopic studies. The present paper also discusses the damage found in the epithelial tissue of the host fish likely due to parasitisation. © Published by Central Fisheries Research Institute (CFRI) Trabzon, Turkey.