1 1 74 BULLETIN OF THE BUREAU OF FISHERIES. 



It is important to notice that the same authors also recognize a second 



subspecies, and this may be the form from which were obtained the parasites 



reported by »Stafford (1904) and already commented upon. Concerning this 



subspecies, Jordan and Evermann write that Salmo salar is — 



* * * represented in Lake St. John, Saguenay River, and neighboring waters 

 of Quebec by the landlocked Salmo salar ouannnirke McCarthy MS., new subspecies. 

 Still smaller, rarely reaching a weight of 7K pounds and averaging 3^2. An extremely 

 vigorous and active fish, smaller and more active than ordinary salmon, but so far as 

 known not structurally different. Saguenay River, Canada (outlet of Lake St. John), 

 and neighboring waters. 



Were it possible to determine definitely whether the records of Stafford 

 concern the oceanic form caught during its migration or the landlocked form, 

 a more definite value could be placed upon his data. In the absence of such 

 information one can not venture to use these records at all in the discussion 

 of the biological problems concerned. What these problems are will be clearer 

 after a more detailed consideration of the case. 



SOURCE OF PARASITES. 



In view of the close specific connection of the two forms, the European sal- 

 mon just considered and the Sebago salmon, a comparative study of their para- 

 sitic fauna is of unusual interest, especially since the Atlantic salmon spends 

 the greater part of its life in salt water, and after its entrance into fresh-water 

 streams in the course of its migration docs not in most cases partake of any food. 

 Consequently whatever parasitic guests it harbors must, as already explained, be 

 of marine origin. The exceptions to this statement are due to accidental infec- 

 tion, and are both small in numbers and insignificant in variety and relative 

 importance. On the other hand, the landlocked Sebago salmon never enters 

 salt water. Its period of active feeding and growth is passed in inland waters, 

 those of Sebago Lake in the case of the specimens we secured and examined. 

 Whatever parasites it harbors are hence obtained in that lake, and are either pure 

 fresh-water organisms or such as have been introduced with the host and subse- 

 quently acclimatized to a fresh-water existence. In the case of such parasitic 

 species as undergo direct development, like many nematodes, the introduction of 

 a marine parasite into fresh water involves the habituation of the free living stage, 

 either egg or larva, or both, to the limnetic environment, and this is the identical 

 process involved in the transfer of any free living organism from a marine exist- 

 ence to one in fresh water. In the case of parasites which manifest indirect 

 development with change of host the case is much more complicated. Such 

 parasites usually have one or more brief stages of free existence in the open 

 water as egg, embryo, or lars'a, like those just referred to. But they also employ 

 one or more intermediate hosts, in which certain parts of the development are 

 passed. Now, either the same marine animals which ser\'e as intermediate 

 hosts in the sea must be found in fresh water also, or must be successfully 



