The occurrence and infection level of parasitic Copepod, Clavella adunca on the black rockfish, Sebastes melanops at the Hatfield Marine Science Center Aquarium were studied. C. adunca was usually found on the base of fins, preferably on the pectoral fins. Seven specimens of black rockfish, Sebastes melanops were collected from Oregon Coast Aquarium. Copepods of ten Clavella adunca were present as ectoparasites attached to the fins in the black rockfish. The prevalence and relative density of Clavella adunca were 28.6% and 1.4 respectively. It is considered that the tissue of the fin membrane offers the most favorable conditions toy the attachment of C. adunca.