ARTIFICIAL PROPAGATION OF TROUT. 73 



Closely watching the movements of the fish the symptoms can usually be de- 

 tected before an alarming stage is reached. 



V.'hen the gills are affected, tlie fish as a rule swim high in the water in an 

 uneasy restless manner, as if gasping for breath. As soon as such a condition 

 is detected the gills should be examined for inflammation or swelling. In 

 the case of a skin disease the fish ordinarily indicate its presence by rubbing 

 on the bottom of the trough or against any convenient surface. They dive 

 with a quick twisting motion against the trough bottom. If the disease is not 

 promptly checked it will soon reach a stage where nothing can be done. 



One of tlie best remedies known for both these disorders is salt, which is 

 sprinkled through the ponds or trouglis after the water has been drawn low, 

 about half a pint of salt being used to each gallon of water. In extreme 

 cases the fish are always treated in the troughs, and in addition to the 

 salt a half pint of apple vinegar is allowed to each gallon of water. These 

 are the proportions for large fish ; for lots which are small and weak the 

 proportion of both salt and vinegar must be reduced. The fish are closely 

 "watched and allowed to remain in the solution only until they begin to turn 

 on their sides, showing plainly that they have stood all they can endure. 

 Fresh water is then turned on freely and distributed among the fish with the 

 hand. As the fresh water fills the trough a slimy white scum rises and floats 

 on the surface of the water. 



Fungus, " blue-swelling," and other affections sometimes occur, but the most 

 serious diseases of fry are those just described. 



During the dry weather of summer fry and fingerling fish are frequently 

 affected by external parasites, which usually make their appearance imme- 

 diately after a rain following a drought. They first attack the tail and fins of 

 the fish, sometimes forming a fringe around the outer fin edges, and after 

 consuming the slimy coating within reach they move up toward the body of 

 the fish, leaving nothing behind them apparently except the bony sinews of 

 the fins. Under such conditions the fish soon weaken and die, when the 

 parasites leave them for other victims. 



Under the microscope the parasites appear to be small white worms, almost 

 transparent, about 0.4 mm. or one-sixtieth-inch long and larger at one end 

 than the other. The mouth is at the small end, and at the other are claw- 

 like tentacles with which they fasten themselves to the fish. They appear 

 to be continuously feeding upon the slimy coating of the fish, stretching 

 themselves at full length and then drawing up until they resemble tiny rice 

 grains. Their presence is indicated by the following symptoms: The color of 

 the fish changes to a dark bluish-black ; the fish swim high, dart around 

 restlessly, and in the last stages turn their tails to the current or seek quiet 

 corners and remain there until they die. 



At some of the bureau's stations where it has been found necessary 

 to treat fish for parasites from one to three times each season it is 

 customary to turn the fish from two adjoining troughs into one. 

 The empty trough is then thoroughly cleaned, wiped with a cloth or 

 sponge saturated with vinegar, and allowed to fill with water. If 

 proper care is exercised in making the solution and the fish are 

 handled carefully, this remedy will be found to work perfectly. 

 The salt treatment alone merely causes the parasites to abandon the 

 fish for a short time; it does not kill them, and they will resume 

 their attack when the water supply again becomes normal, 



A very serious disease is sometimes encountered with adult rain- 

 bow trout. Very dark spots, ranging in number from 2 or 3 up to. 

 20 or 30 and in size from one-fourth inch to 1 inch in diameter, ap- 

 pear on different parts of the body ; a light spot about the size of a 

 green pea forms on the head immediately over the brain. The fish 

 refuse food and become restless; they jump and dart around as 

 though frightened, settling back on their tails; they hide among 

 the plants, seek shallow water in the corners of the pond, and finally 

 sink to the bottom, dying within 24 hours after the appearance of the 

 first symptom. 



