SCHIZAMCEBA SALMONIS, A NEW AMEBA PARASITIC IN 
SALMONID FISHES 
& 
By H. S. DAVIS, Ph. D. 
Fish Pathologist, U. S. Bureau of Fisheries 
CONTENTS 
Page 
Introduction and methods 1 
The trophozoite 1 
Structure of cj T sts 3 
Development of cysts 4 
Systematic relationship 6 
Page 
Distribution 7 
Relation to host 7 
Other amebse in trout 7 
Bibliography 8 
INTRODUCTION AND METHODS 
During the course of an investigation on the intestinal protozoa of trout it was 
found that an ameba which exhibits a number of very interesting characteristics 
is common in these fish. Unlike the parasitic ameba; of other vertebrates, this 
species lives in the stomach rather than in the intestine, only the cysts being found 
in the latter organ. This ameba is evidently widely distributed, since it has been 
found in a number of localities east of the Mississippi River and on the Pacific coast. 
Nor is it restricted to any one species of fish, having been found in several species 
of trout and salmon, but it is probably confined to the Salmonidae. 
Practically all of the material for this investigation was obtained at the Bureau 
of Fisheries’ station at White Sulphur Springs, W. Va. Since the amebse die very 
quickly when removed from the stomach, nearly all my observations have been 
based on preserved material. For this purpose the mucus covering the epithelial 
lining of the stomach was scraped off with a scalpel and smeared as quickly as 
possible over a cover glass, which was at once dropped into a fixing solution. 
Worcester’s formol-sublimate-acetic fluid was found to give the best results, although 
Schaudinn’s fluid was also found to be of considerable value. Both smears and 
sections were stained with iron-hematoxylin, which was found to give excellent 
results when properly decolorized. 
THE TROPHOZOITE 
As stated above, the trophozoites are found only in the stomach, where the 
organism is often very abundant in the mucus covering the epithelial lining. The 
living amebse are colorless and very transparent, showing a faintly granular structure 
of the protoplasm within which the nuclei are usually easily distinguishable. No 
1 
