74 U. S. BUREAU OF FISHERIES. 



This disease was first encountered among a lot of von Behr 

 (brown) trout that had been delivered at the bureau's IVytheville 

 (Va.) station on November 29, 1895. The first symptom was noted 

 six days after their arrival, and by December 12, one week later, 

 455 of them had died. During its first stages the fish were in the 

 nursery, and the water in which they were being held passed through 

 an empty pond into a second one containing about a thousand large 

 rainbow trout that had spawned recently. On the morning of 

 December 23 the disease was apparent among the rainbow trout, and 

 by 4 O'clock of that day 56 had died. The water in the pond was 

 drawn down promptly to about 300 gallons, and 150 pounds of com- 

 mon salt was sprinkled through it. After holding the fish in this 

 brine for 15 minutes fresh water was turned on freely and good 

 results were at once noticeable. The fish became quiet and improved 

 steadily, making a second application unnecessary. The final out- 

 come of the experiment was that the mortality among the rainbow 

 trout amounted to only 30 per cent, whereas the death rate on the 

 untreated von Behr fingerlings exceeded 71 per cent. 



Foul ponds cause disease, and when fish become affected from 

 that cause they must be removed at once to a clean pond and given 

 a salt and clay bath, applying it in the following manner : While the 

 salt bath previously described is being given, from 2 to 3 bushels of 

 clay are placed in the reservior or supply trough, and when fresh 

 water is turned on after the salting the pond is flushed for about 30 

 minutes with roily water from the clay, and after the clay water has 

 passed an increased supply of water is maintained for 10 days or 

 more. 



Adult fish which have been bruised or scarred or have become 

 emaciated are very liable to develop fungus. If the trouble origi- 

 nates from an injury, it can often be cured before it spreads to the 

 sound flesh, but after the growth has spread like a slimy web over 

 the entire body of the fish the case is hopeless. During the spawning 

 season fish are especially susceptible to fungus, and they must be 

 handled very carefully to avoid bruising or scarring in any way. 

 If fungus makes its appearance, the affected fish should be caught and 

 the diseased part treated with salt and with the vinegar solution. 

 It should then be placed in a separate pond or tank with the view of 

 giving it further treatment a clay or two later. Any fish that are 

 affected over the entire body should be removed from the pond at 

 once and killed. 



Thyroid tumor is not an uncommon ailment among artificially 

 reared trout. It affects the gills and may be encouraged by a gener- 

 ally run-down condition of the fish or by insanitary conditions in 

 and about the ponds and troughs. As preventives of disease, plenty 

 of fresh water, scrupulous cleanliness, and the utmost care in han- 

 ' dling eggs, fry, or adults are all-important factors. Many of the ail- 

 ments to which the eggs under incubation and the fry in the early 

 stages of development are subject — " white spot," " blue sac," etc. — 

 may be traced, as a rule, to careless and improper methods of taking 

 the spawn or handling the eggs during the incubation period. Sand 

 sprinkled generously on trough or pond bottoms will facilitate the 

 removal of the coating of slimy substance that frequently forms, and 

 a small amount of salt occasionally mixed with the food is beneficial. 



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