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.

Spores of Chloromyxum trijugum Kudo from Lepomis macrochirus Rafinesque and Chloromyxum catostomi Kudo from Notropis dorsalis (Agassiz) were obtained from infected gall bladders, glass-bead sonicated, and examined by scanning electron microscopy. Valves of C trijugum spores each have a thick ridge running parallel to the sutural ridge. Uncapped cnidocyst pores open into the extrasutural ridges. A pyriform structure of unknown function was observed at the posterior surface in some spores. Spore valves of C catostomi are sculptured with ridged striations running in various parallel and converging patterns over the entire surface. Cnidocyst pores open into ridges adjacent to the sutural plane. Glass bead sonication was found effective in polar filament extrusion. Discharged filaments were twisted along the long axis and partially coated with mucoid globules.