ARTIFICIAL PROPAGATIOIS^ OF TROUT. 67 



size or age is hardly practicable, and hope of eradication must lie 

 along other lines. Sanitary conditions in and about the hatchery 

 are undoubtedly important in this connection, and it has been :^ug- 

 gested that some of these diseases may be carried in the eggs of fish 

 that are ''carriers" of disease. Eggs taken from such trout would 

 seem almost certain to have mixed with them matter from the intes- 

 tinal tract that would contain these organisms. It is possible that 

 these might survive and develop in such a manner as to infect the fry. 

 The Twelfth Annual Report of the New York Conservation Com- 

 mission for 1922 contains a description of some of the parasitic dis- 

 eases common to trout under domestication, and the following notes 

 on the subject are extracted therefrom : -" 



Hatclienj diseases. — ^All fish hatcheries suffer annual losses of fish from 

 disease. The combating of tliese maladies and the keeping of the losses from 

 them within bounds presents one of the most serious problems of fish culture. 

 There is wide variation between hatcheries as to trouble with disease. Some 

 are practically free from epidemics, in others disease conditions are so 

 severe as to restrict the kinds of fish which can be reared in them. The 

 most obvious diiference between hatcheries is the water supply, and it was 

 decided to make a study of that feature as throwing valuable light on the 

 water conditions most favorable to fish life. Such information is needed 

 for the setting up of standards for the permissible pollution of streams. 



Ground covered. — Recurrence of an epidemic of "whirling sickness" among 

 the brook trout fry at Bath hatchery was reported early in the season, and the 

 whole problem at that hatchery was given intensive study. Later the other 

 hatcheries were examined for this and other diseases. Most diseases found 

 were given some study, but special efforts were directed toward the par- 

 ticular disease above mentioned. • 



OCTOMITIASIS. 



"Whirling sickness" or "gill trouble." — This disease is of long standing 

 and practically universal. It attacks all kinds of trout and may cause heavy 

 mortality. It is causetl by a minute parasite of the intestine ( Octomitus 

 salinoni.<i). The symptoms of what appears to be this disease have been 

 described and the causative organism, or one closely allied to it, has been 

 figured, but the two seem heretofore not to have been connected. 



Si/mptoms of the disease. — Apparently this disease is confined to the intes- 

 tines, and no external lesions have been thus far observed. Badly infected 

 trout fingerlings have a characteristic behavior which aids in diagnosing the 

 disease. Balance seems easily lost, and the fish turn over repeatedly with 

 a " whirling " or " corkscrew " motion in the water. Too weak to make 

 headway against the current, numbers of them are found in the corners at 

 the foot of the trough or nosing along the sides near the surface. They lie 

 on their backs with gills distended and in feverish action. The walls of the 

 intestines themselves become translucent, whitish or yellowish in color. 

 They are filled with a watery fiuid, in which the active organisms swim 

 about. * * *. 



Distribution. — Probably this disease exists in wild fish, but under natural 

 conditions causes little harm or inconvenience. In the crowded condition of 

 a fish hatchery the disease seems to be aggravated and may assume the pro- 

 portions of a deadly epidemic. It was found in all our trout-rearing hatch- 

 eries, but was not serious in all. Until more is known of the disease this 

 difference can not be explained with certainty. Adverse conditions in the 

 water supply may well contribute to the intensification of the malady. Thus, 

 water low in dissolved oxygen, or high in deleterious substances, might 

 lower the degree of resistance of the fish to the disease. Further study of this 

 relation is needed. 



Transmission. — Octomitus .'talmonis in ordinary form probably can not long 

 exist outside of the intestinal tract of the fish. It can not readily be de- 



=» Diseasps of Fish in State Hatcheries. By Emmeline Moore. Twelfth Annual Report 

 of the New York Conservation Commission for 1922 (1923i, p. 66. Albany. 



