88 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



that are raised in troughs and tanks in a healthy state, it is well to give 

 them a salt bath occasionally, and a small quantity of salt in their food 

 will at times do them good. A little sediment from the reservoir, or 

 such as collects on stones in the streams, is beneficial to fish if mixed 

 with their food. It seems proper that they should have something of 

 this nature, since all or nearly all of their natural food contains more 

 or less sediment of the kind, 



A very serious disease among adult rainbow trout shows the follow- 

 ing symptoms: The afflicted fish refuse to take food, and very dark 

 spots, from ^ to 1 inch in diameter, appear on different parts of the body, 

 varying in number from two or three np to twenty or thirty on each 

 fish affected, a light spot about the size of a green pea appearing on 

 the head immediately over the brain. The fish become restless and 

 seek the shallow water in the corners of the pond, hiding among the 

 plants, and begin to die within twenty four hours from the time the dis- 

 ease is noticeable. They jump and dart around in the water in a 

 frightened manner, settling back on their tails and sinking to the 

 bottom of the pond in their last struggles. This disease made its 

 appearance at Wytheville in December, 1895; it was first observed 

 among a lot of 037 yearling Yon Behr or brown trout that had been 

 delivered at the station on i^ovember 29. The first sign of the disease 

 was noted about the 5th of December, and by the 12th of the month 

 455 of the G37 fish were dead. 



These fish were in the nursery during the first stages of the dis- 

 ease. The water in which they were held passed from them through an 

 emi)ty pond into a second one containing about 1,000 large rainbow 

 trout that had recently been stripped of their spawn. On the morning 

 of December 23 the disease made its appearance among the latter, and 

 by 4 o'clock in the afternoon of the same day 5G of them had died. 

 Salt was applied and the water in the pond was drawn down to about 

 300 gallons, and 150 pounds of common salt were sprinkled evenly 

 through it. The fish were allowed to remain in this brine about 15 

 minutes, when they showed signs of weakening by turning on their 

 sides ; then fresh water was turned on freely. Good results were at 

 once noticeable, the fish became quiet and appeared to rest more easily, 

 and steadily improved, another application not being necessary. The 

 final result was that 70 per cent of the adult rainbow trout that had 

 been treated with salt were saved, while of the yearling brown trout 

 that were not thus treated nearly 71^ per cent died. 



Foul ponds cause disease, and if the fish become sick from this reason, 

 they must be removed to a clean pond at once and given a salt-and- 

 clay bath, which is applied as follows: While the salt bath, before 

 described, is being given, 2 or 3 bushels of clay are placed in the 

 reservoir or supply-trough, and when the fresh water is turned on after 

 salting, the reservoir is flushed for 30 minutes with roily water from the 

 clay, and after the latter is washed away an increased amount of fresh 

 water is turned on for ten days or more. 



