16 U. S. BUREAU OF FISHERTES. 



LINSEED MEAL A CAUSE OF TROUT DISEASE. 



Some time ago a peculiar disease appeared at a commercial trout 

 hatchery in Rhode Island among yearling and 2-year-old brook trout. 

 The fish turned black, many became blind, and large numbers died. 

 Just previous to death an affected fish would dart rapidly about, 

 sometimes jumping entirely out of the water. After swimming 

 nervously in this way for a few seconds, the fish would usually turn 

 partly on its side, remain quiescent for an instant, and then resume 

 its former unnaturally sluggish swimming. In most cases the fish 

 would repeat this performance several times before finally succumb- 



Dr. L. H. Almy, then fish pathologist in this Bureau, was detailed 

 to an investigation of the trouble. It was learned that the disease 

 had manifested itself a few weeks after the superintendent had 

 begun feeding with a mixture of linseed meal, wheat middlings, and 

 meat scraps, the linseed meal having been substituted for cottonseed 

 meal previously used. When the meat scrap, with flour and salt, 

 was used without the lin.seed meal, the disease was definitely checked 

 in both adult fish and fry. Experiments planned by the fish pathol- 

 ogist were then undertaken at the same hatchery to ascertain which, 

 if either, of the two meals had brought on the disease. The results, 

 which were but recently completed for publication, proved that lin- 

 seed meal was responsible for the pigment change, blindness, and 

 death; that linseed oil in the food of trout has a slightly injurious 

 effect; and that fish affected with linseed-meal poisoning can be 

 brought back to a healthy condition, except for the pigment change 

 and blindness, by a diet of some fresh-meat product. 



Further experiments conducted at the White Sulphur Springs 

 (W. Va.) hatchery of the Bureau, with the cooperation of Supt. R. K. 

 Robinson, gave clear evidence that the pigment change, excitability, 

 and weakened eyesight or blindness were due primarily to the 

 prussic-acid constituent of linseed meal. The experiments indicated 

 also that a food mixture consisting of wheat middlings and meat 

 meal, although not injurious and apparently an acceptable food for 

 the fish, does not compare with fresh hog lungs as a food for yearling 

 trout. 



SERIOUS 'disease OF RUFFALOFISH. 



A new bacterial disease of fresh-water fishes has been under investi- 

 gation (luring the last two summers by Prof. H. S. Davis, temporary 

 investigator. This disease seems to attack nearly all species of fresh- 

 water fishes, but is especially destructive to the buffalofishes, crap- 

 pies, and bluegills. It is preeminently a warm-weather disease and 

 is apparently of little importance during the colder seasons of the 

 year. 



The disease is caused by an imdescribed species of bacterium which 

 develops only on the surface of the body and on the gills. On the 

 body it destroys the skin, but never penetrates into the underlying 

 muscles, while on the gills it destroys all the soft tissues. In either 

 case the fish usually succumb within 48 to 72 hours after the appear- 

 ance of the disease. 



