OCTOMITUS SALMONIS, A NEW SPECIES OF INTES^ 

 TINAL PARASITE IN TROUT. 



By Emmeline Moore 

 New York State Conservation Comtnission, Albany, N. Y. 



Author's Note: The preliminary paper under the caption, "Giardiasis, 

 of Trout,*"' was read at the meeting of the American Fisheries Society, 

 Madison, Wis., September 7, 1922. Since that date further study of the 

 organism in question requires a correction in nomenclature, necessitating 

 a shift in generic position from the genus, Giardia, to the genus, Octomitus.. 

 The specific name, s'^lnionis, is retained under the new designation. Revision 

 of the text has been made in accordance with the later findings. 



INTRODUCTION. 



Octomitus salmonis Moore is a flagellate parasite occurring 

 in the intestine of trout. It is widely prevalent in trout-rearing 

 hatcheries, affecting various species in the fingerling stages. The 

 presence of the organism in large numbers produces serious dis- 

 turbances of the intestinal tract attended by evident symptoms 

 of dysentery. The disease may cause serious epidemics accom- 

 panied by high mortality. 



Without doubt the disease octomitiasis caused by Octomitus- 

 salmonis is a very common cause of hatchery troubles. The 

 papers and discussions on fish pathology appearing in recent 

 numbers of the Transactions of the American Fisheries Society 

 have indicated the widespread nature of certain hatchery 

 diseases, variously designated as "gill trouble" by local hatchery 

 men, or as 'Svhirling sickness" by Hayford (1921) and Foster 

 (1921). There is evidence, also, of a close similarity between 

 the symptoms produced by Bacterium truttae, as described by 

 March (1901, 1902) and those of fish afflicted with Octomitus. 

 It seems quite probable that we are dealing with the same 

 disease, whose various manifestations have been studied from 

 different points of view, and that the inciting cause is not a 

 bacterium, but the protozoan parasite, Octomitus salmonis. 



The recurrence this year of an epidemic of "gill trouble" or 

 "whirling sickness" among brook trout fingerlings at the State 



* Awarded the prize for the best contribution on biological InvestlgationB 

 applied to flsh-cultural problems. 



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