ftquatlc ILitt 



11 



be distinguished just under the transpar- 

 ent skin, does not remain long- in this con- 

 dition. In a few days the perfect mos- 

 quito emerges, ready in turn to propagate 

 its species. 



Linseed Meal Cause of 

 Disease Among Trout 



Some time ago a peculiar disease ap- 

 peared at a commercial trout hatchery in 

 Rhode Island among yearling and two- 

 year-old trout. The fish turned black, 

 many because 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 un- 

 naturally sluggish swimming. In most 

 cases the fish would repeat this perform- 

 ance several times before finally suc- 

 cumbing. 



Dr. L. H. Almy, then fish pathologist 

 in this Bureau, was detailed to an investi- 

 gation 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 linseed meal, the 

 disease was definitely checked in both 

 adult fish and fry. Experiments planned 

 by the fish pathologist were then under- 

 taken at the same hatchery to ascertain 

 which, if either, of the two meals had 

 brought on the disease. The results 

 served to establish the following points : 



( i) Of the two vegetable meals, linseed 

 and cottonseed, the linseed meal alone is 

 responsible for causing the pigment 

 change, blindness, and death. (2) The 

 causative agent is contained in the non- 



oil constituents of the linseed meal. (3) 

 Linsed oil in the food of trout has a 

 slightly injurious effect upon the fish. (4) 

 Fish affected with linseed-meal poisoning 

 can be brought back to a healthy condi- 

 tion, except for the pigment change and 

 blindness, by a diet of some fresh-meat 

 product. (5) Yearling trout on a diet of 

 hog lungs gained in weight three times as 

 fast during three months as those receiv- 

 ing the wheat-meat-meal mixtures ; how- 

 ever, a three times greater gross weight 

 of food was consumed in the former case 

 than in the latter. 



Further experiments were then under- 

 taken at the White Sulphur Springs ( W. 

 Va.) hatchery of the Bureau, with the 

 co-operation of Superintendent R. K. 

 Robinson, to determine more definitely 

 the nature of the toxic non-oil constituent 

 of the linseed meal. These experiments 

 afforded clear evidence that the outward 

 manifestations of the disease brought 

 about in trout by the ingestion of linseed 

 meal — viz., pigment change, excitability, 

 and weakened eyesight or blindness — are 

 due primarily to the prussic-acid constit- 

 uent of linseed meal. The experiments 

 indicated also that a food mixture con- 

 sisting of wheat middlings and meatmeal, 

 although not injurious and apparently an 

 acceptable food for the fish, does not 

 compare with fresh hog lungs as a food 

 for yearling trout. — Fisheries Service 

 Bulletin. 



At the recent Philadelphia exhibition 

 of aquarium fishes an urchin was listen- 

 ing in amazement to the remarks of a by- 

 stander who seemed to know "all about 

 'em," and was accordingly credited in the 

 mind of the youngster with a great and 

 varied collection. The boy wanted some 

 fishes for an unused aquarium at home, 

 but even a ten-cent goldfish was beyond 

 his little purse, so finally he engaged the 

 gentleman in conversation and asked if 



