REPORT OF THE COMMISSIONER OF FISHERIES. 55 



Derby and otlior ])la('os, and ospccially I ho \vasta<2jo of water, lias 

 reduced the level of the river in many i)hK'es to such an extent as to 

 prevent the passa*;e of fish, and in the spring of 1912 thousands of 

 dead trout, from 2 to 3 feet long, were strewn along the bars and 

 clogged the ripples. These largely preventable conditions resulted 

 in the loss of tons of valuable food fishes. 



FISH DISEASES. 



During the fiscal year the usual number of diseases developed 

 among the fishes at the several hatcheries, but as the Bureau is not 

 provided with a regular pathologist nothing could be done toward 

 study and alleviation of the trouble. The makeshift previously 

 adopted of detailing to this work for limited periods an expert whose 

 services were urgently required for other duties pertaining more 

 strictly to his position was no longer feasible. 



It has been possible to make tests of water suspected to be inimical 

 to fishes and to cooperate in a minor capacity with a State institu- 

 tion in the study of the tumor disease prevalent in trout. The latter 

 work has reached a stage in which concentrated effort to that end 

 would probably soon result in the discovery of a remedy, but the 

 Bureau's collaborators are prunarily interested m other phases of the 

 investigation and the Bureau is hampered by the lack of an assistant 

 qualified for this highly specialized research. In the interests of 

 economy of operation of the Government hatcheries, and to the end 

 of saving much valuable food now in the streams, the Bureau should 

 l)e provided with means for carrying on research concerning the 

 diseases of fishes and the methods by which they may be rendered 

 less destructive. 



STUDIES OF PACIFIC COAST SALMONID^. 



The investigations respecting the salmons of the Pacific coast, to 

 which reference has been made in previous reports, have furnished 

 long-sought information concerning important facts in the life history 

 of these fishes. These results have been obtained by the recently 

 developed method of studying the scales, by means of which many 

 facts in the actual history of individual fishes may be determined, 

 and by the multiplication of such studies valuable data concernmg 

 the composition of schools or runs of the species are obtahied. 



In these investigations it has been learned that the various s])ecies 

 of Pacific coast salmon difler more or less m the age of maturity, 

 and that moreover the runs of some species are not homogeneous in 

 their composition but contain varying proportions of individuals 

 younger and older than the normal. Various other facts bearing 

 on the relative proportion of the life of these fishes spent in the 

 rivers and the sea respectively are being developed by the inquiry 

 and wnll be show^n in forthcoming papers on the subject. 



