American Fisheries Society. 67 



In the experience of the commission the disease affects chiefly 

 yearlings, but also fry. The first symptom is a loss of activity in 

 the trout. The individual becomes weak and is not ambitious 

 enough to stem the current of the pond, and perhaps allows it to 

 drift him against the screen at the lower end. He does not at- 

 tempt to avoid the net and is easily taken. He still remains 

 riglit side up, breathing quietly. He is apt to make spasmodic 

 efPorts to swim, but does not go far and turns partly over in the 

 attempt. This is the beginning of a loss of equilibrium, which 

 becomes complete, and the trout lies on his back or side at the 

 surface or bottom, gasping. After occasional proxysms or frantic 

 dashings in apparent great distress, death soon occurs. 



Examined post mortem these trout have not fallen off much 

 if any in condition. ]\[ore than half of them have no external 

 marks of disease and these look like fine healthy fish. But some 

 have very plain external lesions, the essential feature of which is 

 an extravasation of blood into the tissues. It is seen chiefly in 

 the muscles, and appears in its simplest manifestation as a mere 

 red streak or patch, or bloody blotch, Mobile its ultimate or ex- 

 treme condition is an ulcer. All intergradations between these 

 two stages may be seen. That is to say the blotch of blood com- 

 mences to liquefy the muscle surrounding it and the place be- 

 comes soft to the touch. It swells slightly or considerably, and 

 may make an elevation or puffy swelling which looks like a pus- 

 tule or boil. This is usually red or purple in color and rather 

 soft or yielding, l)ut sometimes slightly tense when the skin re- 

 mains firm, showing the existence of some pressure from within. 

 These are found on comparatively few of the dead fish as they 

 usually die before reaching this stage. The skin finally sloughs? 

 and makes an ulcer. The location of these lesions may be any- 

 where on the trout, but favorite places are the bases of the fins, 

 most often the pectoral, and the sides of the head. There are but 

 few internal evidences of disease visible to the naked eye. 



These boil-like elevations are not boils nor abscesses proper, 

 for they do not contain pus and the infection is not a suppura- 

 tion. Their contents are a bloody liquid which consists of the 

 .serum of the blood, some red corpuscles and a good many white 

 <ones, degenerated muscle fibres, and countless numbers of bac- 



