10 
BULLETIN OF THE BUREAU OF FISHERIES 
NOMENCLATURE 
Octomitus salmonis was first described by Dr. Emmeline Moore (1922), who 
found it in several species of trout at the New York State hatcheries. Investiga- 
tions of the parasite were begun almost simultaneously in the spring of 1922 by 
Doctor Moore and the writer, who had independently discovered it in rainbow and 
brook trout from the White Sulphur Springs (W. Va.) hatchery. 
Octomitus salmonis belongs to the family Hexamitadse, which, according to 
Alexeieff (1914), includes the four genera, Hexamitus, Octomitus, Giardia, and 
Trepomonas. It is not the writer’s intention at this time to enter into the con- 
troversy relative to the distinctive characters of the genera Hexamitus and Octo- 
mitus. This matter has been discussed at length by Dobell (1909), Alexeieff 
(1914), Swezy (1915), and Moore (1922). It is believed that there are valid 
grounds for distinction between the two genera as pointed out by Alexeieff. This 
distinction should be based not on a difference in habitat, as proposed by Dobell, 
but on strictly morphological characters, since the three genera, Hexamitus, Octo- 
mitus, and Giardia, can be clearly distinguished by the character of the flagella. 
As pointed out by Alexeieff (1914), the three pairs of anterior flagella in Hexamitus 
arise directly from the basal granules. In Octomitus there is a short rhizoplast 
surrounded by a differentiated layer of protoplasm between the basal granules 
and the flagella, while in Giardia the rhizoplasts are much longer and better de- 
veloped than in Octomitus. The second characteristic — that of the fusion of the 
axostyles for part of their length — is believed to be based on an error in observa- 
tion, since it is very doubtful if the axostyles are ever fused in either of the three 
genera, although they may sometimes be so close together as to appear fused on 
casual observation. The -writer has several undescribed species of Octomitus and 
Hexamitus from various fishes, but in all cases the axostyles are distinct through- 
out their length. Probably another characteristic of Octomitus is a specially 
modified region at the anterior end, which forms a primitive cytostome but without 
the dorso-ventral flattening so characteristic of Giardia. 
It will thus be seen that Octomitus occupies an intermediate position in the 
phylogenetic series between Hexamitus and Giardia. Hexamitus undoubtedly 
represents the primitive type from which the other two genera have been developed, 
while in Giardia we have the forms that are most highly specialized for a parasitic 
mode of fife. 
DISTRIBUTION 
Octomitus salmonis is widely distributed throughout the country, having been 
reported from trout hatcheries in New England, New York, New Jersey, Virginia, 
West Virginia, Iowa, and Missouri, and it is probable that very few hatcheries are 
free from the parasite. It has also been found in young salmon from hatcheries in 
Washington, Oregon, and California. The parasite has not yet been found in wild 
trout except under circumstances that indicate that the infection was probably 
derived from hatchery fish. However, there is no reason to doubt that it does 
occur naturally in wild trout, but it is probably rarely abundant under such cir- 
cumstances. No doubt the hatcheries first became infected from wild fish, the 
