Abstract
Migrating Atlantic salmon (Salmo salar), captured during their ascent of the fishway at the lowermost dam on the Penobscot River, were examined for external parasites and lamprey (Petromyzon marinus) wounds. At least one of three species of sea lice (parasitic crustaceans), Argulus canadensis, Caligus elongatus, and Lepeophtheirus salmonis, was observed on 189 of the 2,045 fish examined. Eighty-three salmon had lamprey wounds, with two of these fish also carrying lice. While lamprey wounds occurred on multi sea- winter fish in June and July, lice were observed almost exclusively in July on one sea-winter salmon (grilse) and multi sea-winter fish. Both groups of para- sites infected male and female fish in proportion to fish sexes in the population. Fish parasitized with lice carried an average of 3.5 lice/fish, with a range from one to 33. Most of the copepods were pre-adult, indicating recent attachment to the host. The numbers of parasites on migrating salmon in the Penobscot are
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