22 2 TWELFTH ANNUAL REPORT OF THE 



Outwardly the disease shows itself in a more or less intense redness of 

 the skin on the belly and sides. In the scale carp, in most cases, it is 

 scarcely noticeable, in others, especially in leather and mirror carp, it is 

 evident at a glance. Not only does the whole underside of the fish appear 

 suffused with blood, but the lower fins also show blood red. On account of 

 these marks, the disease is called " The Red Plague." 



The red color of the skin is produced by an abnormal enlargement and 

 overfilling of the vessels of the skin, as well as by effusion of blood in the 

 skin itself. The appearance of the skin, however, is not the only symptom 

 of the disease. The gills, also, are sometimes more or less decayed — broken 

 down by necrosis. They have become as the experts express it, blighted 

 and fouled. Small hemorrhages, moreover, are to be seen on them. The 

 intestine very often is badly inflamed and is then not only greatly reddened 

 but sometimes contains a bloody, slimy exudation, and in many cases is 

 entirely eaten with little sores for a distance of almost one-third of its 

 own length. The heart, also, is rather seriously attacked; the pericardium is 

 thickened and is partly or wholly grown together with the heart muscles. 



The cause of the disease exists in an infection of the fish with Bacteria 

 cyprinicida Plehn, which is found in all the organs and is especially bad in 

 the blood and kidney. 



The Red Plague is most virulent when fish are kept in water polluted 

 with foul organic remains. These conditions are especially noticed in fish 

 hatcheries where the bottom of the ponds is strewn with dirty remains — 

 worn shreds of skin, scales, etc., often several inches deep, and where the fish 

 are badly overcrowded. It spreads apparently from one fish to another so 

 that the fish catch the disease giving bacteria through their crowded condition. 



Fish of the carp family infected with the Red Plague which live through 

 a week's duration of the infection are finally destroyed entirely by this dis- 

 ease. A most careful study of the infection shows that death occurs in from 

 five to twenty days. The sick fish are languid, usually rise to the surface, 

 float there aimlessly, sometimes lying on the side, and then, without any 

 sign of suffering, gradually succumb. 



To escape the Red Plague cleanliness is one of the most essential condi- 

 tions. Fish culturists should so arrange their ponds that the dirty remains 

 and shreds of skin may sink to the bottom through an open wooden screen 



