Cooperative Fish and Wildlife Research Units Program: Maine
Education, Research and Technical Assistance for Managing Our Natural Resources

Little research on wild fish and sea lice interactions has occurred in the Northwest Atlantic Ocean, particularly for the sea lice species Caligus elongatus. This project quantified infestations of sea lice on wild fishes of Cobscook Bay, Maine. Field examinations of 6,334 fish during March–November 2012 were used to determine host species and infestation prevalence. Of these, 253 fish were examined under magnification to identify sea lice genus, infestation intensity, sea lice life cycle stages, and attachment locations of chalimus stages. We used DNA sequencing on 175 (34%) individual lice to confirm sea lice species. Caligus elongatus was the only observed sea lice species and was found on 10 fish species, including eight newly identified hosts. Nonmotile chalimus were the predominant life stages observed, accounting for 95.87% of sea lice, and were predominantly attached to hosts' fins. Overall infestation prevalence and intensity among all sampled fish were low—less than 5% and just one sea louse per fish, respectively. Among the three most common host species, Threespine Sticklebacks Gasterosteus aculeatus had the highest infestation prevalence and intensity. These results are the first reported data for sea lice presence on a wild fish assemblage in the Northwest Atlantic Ocean. Furthermore, the identification of new hosts for C. elongatus and the lack of observed infestations by the salmon louse Lepeophtheirus salmonis will be used to inform sea lice management efforts in aquaculture operations.