THE SALMON 49 



attained. The lice are unable to live in fresh 

 water, and a few days after a Salmon has entered 

 a river they drop off. 



In fresh water Salmon may become infested with 

 ' maggots ' in their gills. These so-called maggots 

 (Lernaeopoda salmonea} are very different in appear- 

 ance from the lice, and are still less shrimp-like, 

 although they belong to the same order and resemble 

 them in the structure of the suctorial mouth and the 

 attachment of the larva by a frontal thread. The 

 adult females are only one-fourth or one-third of an 

 inch long, and a pair of appendages are modified 

 into long arms which unite at the tip to form a 

 sucker, which effects the attachment to the gills ; 

 the egg-cases contain several series of eggs. Males 

 of this genus are little known, but are dwarfed, and 

 are sometimes found attached to the females. 

 Maggots can live in the sea, and fresh-run Salmon 

 which have visited fresh water before usually have 

 them in their gills. 



In fresh water also Salmon may become infected 

 with Salmon disease, which sometimes causes great 

 mortality among them. Mr. Hume Patterson's 

 researches, published in 1903, have established that 

 this disease is due to a specific germ which he 

 names Bacillus salmonis pestis. The bacilli invade 

 the body of the fish when the skin has been injured 

 or broken, and multiplying rapidly form areas of 

 mortified flesh which are a suitable soil for the 

 growth of the fungus called Saprolegnia ferox. The 

 white patches of this fungus are usually an outward 

 and visible sign of Salmon disease, although they 

 do not, as was formerly supposed, constitute the 

 disease itself. Sea water destroys the fungus, bijt 



