Ichthyophonus hoferi - MMFS

Science Center Objects

Fish Parasite

Ichthyophonus hoferi

Juvenile Pacific herring with skin ulcers

Juvenile Pacific herring with skin ulcers from Ichthyophonus disease. Credit: Paul Hershberger, USGS - Western Fisheries Research Center. (Public domain)

Ichthyophonus hoferi is a member of the Mesomycetozoea, a monophyletic class of protists that includes several other important pathogens. Currently I. hoferi and I. irregularis are the only two recognized species in the genus, but other species have likely been grouped with I. hoferi based on the plasticity of morphological characteristics. Recent molecular phylogenetic studies indicate that distinct genetic types of the parasite exist; therefore, the organism is often generically as Ichthyophonus. From 1898 through the mid 1950’s, six major Ichthyophonus-related epizootics were described in Atlantic herring from the Western North Atlantic. More recently, a massive Ichthyophonus-related epizootic killed an estimated 300 million Atlantic herring in waters around Sweden and Denmark during the early 1990’s, and epidemiological data implicate Ichthyophonus as a primary factor responsible for mortality in wild Pacific herring from estuarine waters of Washington State. Most recently, a large Ichthyophonus epizootic occurred in the waters around Iceland during the fall and winter of 2008, resulting in the capture of massive numbers of herring that were unmarketable as a result of Ichthyophonus-induced tissue changes.