OCTOMITTJS SALMONIS, A PARASITIC FLAGELLATE OF TROUT 21 
Washington, and it was found that in many instances the anterior end of the in- 
testine was badly inflamed. When sectioned, the congested portion of the intestine 
and caeca were found to contain intracellular parasites in such numbers that a large 
proportion of the epithelial cells was destroyed, which was undoubtedly the cause 
of the inflammation. In striking contrast to the chronic form of octomitiasis, we 
have here an acute disease that results in a heavy mortality within two or three 
days. Evidently the changed conditions to which the fish are subjected during 
distribution result in a sudden and rapid increase in the intracellular stages of 
Octomitus: That this is the case has been shown by a number of experiments in 
which fish have been taken directly from the hatchery troughs and placed in cans 
(such as are used in distribution) for 24 to 48 hours. In every case this has resulted 
in a noticeable increase in the number of intracellular parasites, the great majority 
of which were in various stages of schizogony. The picture presented in sections 
of such material is in striking contrast to that ordinarily found in sections from 
infected fish in which the intracellular parasites are not abundant and division 
stages are the exception. 
There is still some uncertainty as to the factors involved in stimulating the 
development of the intracellular stages, but undoubtedly a rise in temperature, 
deficiency of oxygen, and cessation of feeding are among the more important, 
although it is not necessary for all of the factors to be present to cause increased 
activity among these forms. For instance, when the fish are held in cans placed 
in running water at the hatchery there is usually an increase in the intracellular 
stages although the temperature is constant. However, the increase is not as 
rapid as when the temperature is allowed to rise slightly. That the practice of 
withholding food from the fish during distribution is also a factor is indicated by 
some observations during the past summer. In the course of some feeding experi- 
ments at the White Sulphur Springs station it was necessary on two occasions to 
allow the fish to go two or three days without food, owing to delay in the usual 
shipments of heart and liver. In both instances there was an increased mortality 
after the first day, and in practically every instance an examination of the caeca 
of the dead fish showed that large numbers of intracellular parasites were present 
in an actively growing condition. Strangely enough, the mortality was greatest 
among fish fed on liver, although, as stated above, the flagellates were more numerous 
in heart-fed fish. 
In addition to the mortality during the distribution of fingerlings there is reason 
to believe that severe epidemics, accompanied by heavy mortality, may occur 
under certain conditions while the fish are still at the hatchery. Such epidemics 
occur only sporadically and are not of regular recurrence year after year, as in the 
case of the common chronic form of octomitiasis. While the writer has not had 
an opportunity to conduct a personal investigation of such an epidemic, there is 
evidence that several heavy mortalities at the bureau’s hatcheries in recent years 
were primarily due to this cause, and Dr. Emmeline Moore (1923 and 1924) states 
that a number of severe epidemics in the New York State hatcheries have been 
caused by Octomitus. Such a heavy mortality in a comparatively short time 
suggests that the intracellular stages may have been primarily responsible, although 
it is by no means certain that in some instances, at least, another organism in addi- 
