Infection of the Pacific saury Cololabis saira (Brevoort, 1856) (Teleostei: Beloniformes: Scomberesocidae) by Pennella sp. (Copepoda: Siphonostomatoida: Pennellidae) south of the Subarctic Front

Abstract

Abstract The Pacific saury (Cololabis saira) is a fish of commercial importance subject to unpredictable epidemics of infection by Pennella sp., a parasitic copepod. We analyzed the distribution of fish presenting with newly attached Pennella to determine the region and season in which Pennella first infect the fish. Pacific sauries migrate northward in the spring to spend the summer in the subarctic region, successively crossing the Subarctic Boundary (SAB) and the Subarctic Front (SAF). The fish then return to subtropical waters in the fall and overwinter there. Pacific sauries infected with Pennella were observed on both the north and south sides of the SAF from May to December. Newly attached Pennella, however, were observed mainly to the south of the SAF during the northward migration of the fish in May and June, and only to the south of the SAB during the southward migration in November and December. These results indicate that the intermediate host or hosts of Pennella inhabit the region south of the SAF, with infection of Pacific saury occurring during late fall and spring. Such information may assist in identifying the intermediate host(s).