No parasite common to hatchery salmon and trout possesses quite so varied a reputation as does Octomitus salmonis. Discovered, studied, and described independently, but essentially simultaneously, by Dr. Emmeline Moore and Dr. H. S. Davis,
Octomitus salmonis was introduced to fish culture during the early twenties. This easily found and widely distributed parasite, once recognized, was soon held responsible for practically every ailment noted in trout hatcheries at that time. Such a reputation was doubtless deserved in some instances, but unquestionably many losses ascribed to Octomitus salmonis actually resulted from such troubles as bacterial gill disease, which was then unknown, or from less easily found parasites such as Costia necatrlx. As might be expected, the pendulum of opinion gradually swung to the other extreme.