This study reports a parasite infection of Pennella instructa Wilson C.B., 1917, on Indo-Pacific Sailfish Istiophorus platypterus (Shaw, 1792) in a commercial fishing area off the Ratnagiri coast in the eastern Arabian Sea. It confirms the presence of the Epizoic cirripede, Conchoderma virgatum Spengler, 1789, on P. instructa as commensality attachment. It also confirms that P. instructa and C. virgatum have expanded their range to the North Eastern Arabian Sea.