PROGRESS IN BIOLOGICAL INQUIRIES, 193 4 389 



•svliich formed only 22.2 percent of the total number of orj^anisms 

 taken in one series'of 13 snmples, formed 43.9 percent of the total wet 

 -\vei<rht of all oriranisms, oll"erin<; the most food by bulk of any <^i'oup 

 of aquatics. Mayfly nymjjhs, on the other hand, were most abundant, 

 formin<r over 55 percent by number but only 28 percent by wei<jjht. 

 Stonefly nymphs were third in weif2:ht of food at 12.2 percent and 

 fourth in numbers at 7.8 percent. Aquatic truefly larvae and pupae 

 '(Dii)tera) formed 10.3 jicrcent by number and oidy 7.9 percent by 

 weiii'ht of total available foods. 



Some work was started on the distribution and abundance of 

 stream foods in relation to water temperatures and other ecological 

 factors, but much further field and laboratory work will be necessary 

 before results can be submitted on these phases of the problem. 



nSH DISEASES 



Investigations were conducted by Dr. Frederic F. Fish on the 

 ^' ulcer disease " of trout which he has shown to differ in many 

 respects from furunculosis with which it was formerly confused. 

 The disease is characterized by definite thickening of the epithelium 

 over a small area, producing an inconspicuous white patch which in 

 general apjDearance closely resembles a small growth of fungus 

 (sapolignia). This condition is best described as an "epithelial 

 tuft." Eventually the skin becomes perforated and the small ulcer 

 is formed. When a lesion of the " ulcer disease " develops on a fin, 

 the soft tissue between the fin rays is destroyed leaving the rays 

 projecting beyond the neucrotic tissue. As the disease progresses 

 the neucrotic area advances in a more or less horizontal line toward 

 the base of the fin. In advanced stages of the disease the fin may 

 be entirely destroyed while the infection penetrates deep into the 

 underlying tissue. There is no evidence, however, that the infection 

 ever reaches the internal organs. 



The causative agent of the disease is evidently a bacterium. Sev- 

 eral species of bacteria have been isolated from diseased fish, but it 

 has not yet been possible to demonstrate conclusively that any one 

 of them is the specific etiological agent. 



During the early part of the year Dr. Fish was stationed at the 

 Leetown (W. Va.) station to investigate an epidemic of blue sac 

 which was causing heavy losses among the brook and brown trout 

 fry. In contrast with other investigators. Dr. Fish was unable to 

 find any definite evidence that the disease was due to a specific in- 

 fection. Cultures of the serus fluid gave negative results except in 

 Sj few instances. Sections of the diseased tissue also failed to disclose 

 any evidence of bacterial activity and there was nothing to indicate 

 that the disease spread from one trough to another as is usually 

 the case with bacterial infections. 



During the summer Dr. Fish was detailed to cooperate with the 

 Oregon State Game Commission in a study of fish-cultural problems 

 which had arisen in connection with the operation of the State trout 

 hatcheries. Field headquarters were located at the Oregon State 

 College, Corvallis, and inspection trips were made to all but two 

 minor State trout hatcheries and to many points where the Oregon 

 Game Commission had been carrying on field work. The purpose 



