PROGRESS IN BIOLOGICAL INQUIRIES, 1926 043 
source, but which had been held in spring water, suffered a mor- 
tality of only about 10 per cent. The cause of the excessive losses 
among these fish has not been determined definitely. Some of the 
loss undoubtedly was due to an infection with the protozoan parasite, 
Octomitus salmonis, and there is little doubt but that the mortality 
among the fish in spring water was due almost entirely to this para- 
site. However, another factor appears to have been involved in the 
heavy mortality among the fish in brook water. It is possible that 
the fish were weakened as a result of retarded development caused by 
the low temperature of the brook water. It is interesting to find that 
a similar mortality has occurred annually in several State hatcheries 
where the eggs are held in cold water to retard their development. 
In fact, the information at hand indicates that the common practice 
of holding eggs at a temperature just above freezing is objectionable 
and often results in greatly lowered vitality. 
Octomitiasis has been prevalent at Holden for a number of years, 
and the losses from this disease were so large that all attempts to 
hold fingerling trout through the summer had been abandoned. 
However, during the past two summers, since the station has been 
used as an experimental hatchery, fingerlings have been carried 
through the summer with comparatively little loss from this disease. 
It has been found that while it is virtually impossible to get rid of 
Octomitus entirely, the severity of the infection can be reduced 
greatly by rearing the fingerlings in ponds, where they have more 
room than in the hatchery troughs and can obtain some natural food, 
such as insects and Entomostraca. In several instances, fish that had 
become heavily infected with Octomitus in the hatchery, when re- 
moved to ponds showed marked improvement within a week or ten 
days; and at the end of three or four weeks the parasites had dis- 
appeared very largely, the mortality was low, and the fish were mak- 
ing rapid growth. 
In addition to work at the bureau’s stations, the pathologist, at the 
request of the State authorities, visited several State hatcheries to 
investigate the causes for heavy losses among fish at these stations 
and to suggest remedial measures. He was consulted by a number 
of goldfish breeders, also, regarding mortality among their fish. 
In March, 1926, an investigation was made at the Washington . 
laboratory of the mortality occurring at the Central Station aquarium 
following chlorination of the water. Dr. R. S. Taylor, of the division 
of fishery industries, studied the chemical aspects of the problem, 
while M. C. James made observations on the biological phases. It 
was found that trout were killed by the concentrations found in the 
ordinary chlorine dosages (0.3 p. p.m.) of municipal water supplies. 
Survival in spite of such chlorination generally is due to a reduction 
in the concentration through interaction with organic matter and 
aeration. 
A number of chemicals, all reducing agents, were found to be 
effective in eliminating all chlorine in an aquarium supply and at 
the same time were harmless to fish. Among these, sodium bisul- 
phite and sodium thiosulphite were considered most satisfactory. A 
1: 1,000,000 concentration of the former is sufficient to neutralize the 
chlorine usually present in municipal waters, while sufficient thiosul- 
phite must be introduced to give two or three parts per million. 
