Lethal, disseminated infection with an oomycete ( <i>Halioticida noduliformans</i> ) in captive, deep-sea isopods ( <i>Bathynomus giganteus</i> and <i>Bathynomus doederleinii</i> ) in California

There are no previous publications on diseases of Japanese isopods (<i>Bathynomus doederleinii</i>) or giant deep-sea isopods (<i>Bathynomus giganteus</i>). <i>Halioticida noduliformans</i> is a pathogenic oomycete that infects external tissues of abalone, mantis shrimp, and European lobsters, and has not been previously reported in isopods. The purpose of this study is to describe the clinical presentation, gross findings, and histologic lesions caused by <i>H. noduliformans</i> in <i>B. doederleinii</i> and <i>B. giganteus</i> kept in a public aquarium in California. Oomycetes caused inflammation and necrosis in the body wall, gills, hepatopancreas, eyes, and gut. Our study demonstrates that this pathogen occurs in a previously unreported geographic location and in previously unpublished hosts. <i>H. noduliformans</i> infected both external and internal viscera, the latter of which has not been previously reported in any host species. <i>H. noduliformans</i> has variable pathogenicity depending on the host species and was considered the cause of death in these isopods.