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Cypriniform and salmonid fishes of the Columbia River drainage of western Montana harbor five members of the myxozoan family Myxobolidae. Myxobolus muelleri inhabits Ptychocheilus oregonensis (northern squawfish), Mylocheilus caurinus (peamouth), Richardsonius balteatus (redside shiner), and Catostomus macrocheilus (largescale sucker). Cysts appeared in gills, musculature, subcutis, and visceral mesenteries. Unencysted spores infiltrated mesenteries and viscera. Spore size and shape in the various tissues and hosts were highly varied. Muscle and subcutaneous cysts were associated with connective tissue proliferation and muscle degeneration; cyst rupture was associated with diffuse inflammation and rodlet cell proliferation. Infection prevalence in muscles and kidneys was high in adult and juvenile hosts (78–100%) throughout the year. Seasonal prevalence of gill and subcutaneous infections fluctuated markedly. Cysts of Myxobolus dujardini occurred in gills of the northern squawfish, peamouth, and redside shiner. Unicauda sp. was found in the eye capsule, gall bladder, mesenteries, and kidney of northern squawfish. Henneguya zschokkei occurred in intermuscular connective tissue of Prosopium coulteri (pygmy whitefish) and Prosopium williamsoni (mountain whitefish). Myxobolus sp. occurred in the gills of Catostomus catostomus (longnose sucker).

. Severe melanotic liver and visceral fibroses in bluegill associated with infections of plerocercoids of Proteocephalus sp. and metacercariae of the digenean Posthodiplostomum minimum, were studied by light and transmission electron microscopy. Fibrosis was most evident in bluegill carrying heavy worm burdens. Tubular and multilocular melanotic and non‐melanotic cysts were formed of concentric layers of non‐cellular eosinophilic connective tissue surrounding central spaces containing basophilic material. Moribund and deteriorating plerocercoids and metacercariae were surrounded by, and sometimes invested with, fibrous tissue. Living plerocercoids in the liver were surrounded by necrotic and compressed hepatocyte zones. Fibro‐blasts, epithelioid cells and eosinophilic granulocytes were common in compressed cell zones. Intrahepatic fibrotic cysts were surrounded by granulomatous zones. Parenchyma in fibrotic livers showed increased numbers of macrophages, melano‐macrophage centres and engorged blood vessels with thickened walls. Histochemical tests for lipofuscin and haemosiderin were strongly positive in melanotic liver tissue. Ultrastructural changes in hepatocytes adjacent to fibrotic cysts and epithelioid zones included intranuclear lipid and glycogen inclusions, chromatin alterations and mitochrondrial degeneration. Bile canaliculi, sinusoids and perisinusoidal spaces showed reduced micro villarsurfacesand a decrease in luminar diameter. Degenerating hepatocytes contained phagolysosomes and myelin bodies.

Abstract:The gall bladder parasite, Chloromyxum trijugum, shows marked host specificity within the sunfish family Centrarchidae. During 1977-78 80% of 230 bluegills (Lepomis macrochirus) in Iowa were infected. Prevalence in green sunfish (L. cyanellus) was lower (17%); one of 2 specimens of the hybrid L. macrochirus X L. cyanellus was infected; orangespotted sunfish (L. humilis) and hybrids (L. humilis X L. macrochirus) were not infected. Intensity of infection in bluegills varied throughout the year. Prevalence of free-floating Plasmodia in bluegill gall bladders was highest (100%) during winter and spring months, and decreased to 40-50% during summer and fall. Prevalence of attached plasmodia may remain 80-100% throughout the year. Sporulation and plasmotomy were observed year-round. Plasmodia were attached to underlying epithelial cells by pseudopodia-like projections and were associated with various stages of breakdown in the mucosal layer.

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