28O DOMESTICATED TROUT. 



fungus, which eats into and kills the fish ; and that the fish 

 can be cured, when not too much weakened, by immersion 

 in a strong solution of salt.* 



A similar series of experiments led to the discovery that 

 salt is also a cure for the parasites on young fish. These 

 parasites are smaller than those which infest the large 

 fish.f They have a circular form with a diameter of about 

 -g*j of an inch. They are extremely thin, and progress by 

 a rotatory movement. They sometimes swarm in immense 

 numbers upon the young fish that are attacked by them. 

 They do not cause a fungoid growth, as the larger ones do 

 in the larger fish, but the young trout affected with them 

 appear outwardly as clean and well as ever. If the para- 

 sites are not removed, however, the trout will lose their 

 strength and drift down toward the screen, on which they 

 will probably be finally caught and die. Salt destroys 

 the parasites, and does not injure the young fry. It is, 

 therefore, a remedy for the parasites. Hundreds of ex- 

 periments which I tried of putting the affected young trout 

 in salt water had the same result, which was to kill the 

 parasites and restore the fish. 



I will also add in this connection that the salt bath 

 seems to improve the young fish in other ways than by 

 killing the parasites, and one lot of young fry in particular, 

 confined in a small box, which I cured in this way, and to 

 which I gave a pint of salt every day, appeared better than 



* I used a table-spoonful of salt to a pint of water, and kept 

 the fish in it till he went over on his back, and then took him 

 out and put him instantly into cold running water. 



t I have sometimes found the larger parasites in small num- 

 bers on the small trout, but have never found the circular para- 

 site on large trout. 



J This furnishes one explanation of what so many trout 

 breeders have remarked, that their young fry seemed to die 

 when they appeared perfectly healthy. 



