484 Memoir Sears Foundation for Marine Research 



a serious menace to adult Atlantic Salmon in the Miramichi (M.H.A. Keenleyside, 

 personal communication). 



Parasites and Diseases. Numerous parasites and a few diseases" have been reported 

 for Atlantic Salmon, but it is not known to what extent they affect the population. For 

 the most part, ways and means of controlling them have not been found. Among the 

 external parasites, sea lice {Lepeophtheirus salmonis) and gill maggots {S almincola sahnoned) 

 are common and widespread, and five others have been reported as sometimes occurring. 

 Of the diseases, "Salmon disease" and furunculosis are the more common. 



Sea lice, which occur on Atlantic Salmon throughout their range in both North 

 America and Europe," are parasitic copepods frequently found attached to fish that 

 have recently entered fresh water from the sea. Sea lice usually die within a week of 

 being brought into fresh water, but sometimes they live longer. Most of those attached 

 to Atlantic Salmon are females about three-quarters of an inch long. White observed 

 that some of the fish that entered the Moser River in 1939 were so heavily infested 

 with them and had so much of the skin in the occipital region eroded away that the 

 fish died after entering fresh water {141). The large fish were not so heavily infested 

 as grilse, some of which had an almost complete layer of lice extending over the dorsal 

 part of the body from the posterior edge of the eyes to the caudal peduncle, and a 

 few lice around the anal and ventral fins. Before the skin sloughs away there is a 

 distinct white area over the regions affected; White believes this is the condition de- 

 scribed as "white spot."" 



Gill maggots {Salmincola salmoned) are smaller than sea lice (0.25-0.33 in.), and 

 most of those on Atlantic Salmon are females. Although they are able to breed only in 

 the river, numbers survive in salt water. Maggots attach themselves to the gills of 

 the fish in fresh water, only after the latter have been in salt water and have returned. 

 They are not found on young that have remained in fresh water (jj: 16). Maggots 

 have been found on fish that have been in fresh water for as much as a year and in 

 salt water for two additional years. 



Internal parasites of Atlantic Salmon are reported under more than a hundred 

 names, but until careful taxonomic studies have been made it is impossible to say how 

 many of these represent valid species. Twenty-five names, for example, have been re- 

 ported for trematodes or flukes, 38 for cestodes or tapeworms, 25 for nematodes or 

 round worms, 22 for acanthocephalous or thorn-headed worms, and 8 for Protozoa. 



Furunculosis, the ulcer or boil disease, caused by the bacterium Bacillus salmonicida, 

 has occasionally assumed epizootic proportions in hatcheries, whence it has spread to 

 natural waters; it has also reached similar proportions at times in southern England. 

 A second bacterial disease (Salmon disease), caused by Bacillus salmonis pestis, has 

 occasionally assumed serious proportions in southern England. 



16. Lists of parasites reported for the Atlantic Salmon were provided by the Parasitology Division, Ontario Research 

 Foundation; Animal Disease and Parasite Research Division of the U.S. Department of Agriculture; and Institute 

 of Parasitology, McGill University. 



17. Sea lice also affect brown trout {Salmo trutta), brook trout [Sahielinus fontinalis), Dolly Varden [Sal'velinus alpinus 

 malma), and two Pacific Salmon {Oncorhynchus tshavytscha and O. gorbuscha) {120; 51; 147). 



