| This study examines the morphology, taxonomy, pathology and epizootiology of Ichthyophonus hoferi from yellowtail flounder, Limanda ferruginea, from the Nova Scotian shelf.;I. hoferi was found in the kidneys, heart, liver, spleen, testes, intestinal tract, skeletal musculature, ovaries, brain and gills of L. ferruginea. The fungus was seen as single, or groups of, resting spores, germinating spores and/or small spherical- to irregularly-shaped, amoeboid-like spores in the host tissue stroma. It was also seen within host cells, or in capillaries, kidney tubules and the digestive tract.;In culture, the fungus produced aseptate thalli exhibiting dichotomous branching and apical sporangia. Reproduction was by means of endogenous and exogenous division of sporangia and resulted in the production of aplanospores. The extent and type of thallus growth, subsequent aplanospore production and dimensions of developmental stages were affected by temperature, salinity and oxygen tension.;The resting spore wall is a non-crystalline structure. It is composed of high concentrations of hexose sugars and acidic and sulphated polysaccharides but low concentrations of lipids and proteins. I. hoferi cells contained typical mastigomycotinid organelles. These included a cell wall composed of longitudinally-compressed microfibrils, a paramural endoplasm with lomosomes, endoplasmic reticulum, dictyosomal-derived vesicles and ribosomes, dictyosomes, lipid bodies, mastigonemes in a ribosome-studded cisterna of the endoplasmic reticulum, and electron-lucid patches containing glycogen. Cells also contained organelles associated with higher fungi, and amoeboid and apicomplexan protozoans. These organelles were a pair of electron-dense, oval- to bar-shaped spindle pole bodies associated with the outer nuclear membrane and mitochondria with short, tubulo-vesicular cristae and having an electron-dense crystalline core. Still other features were observed that apparently have not been previously described in lower eukaryotes.;By virtue of the gross and fine structures of the developmental stages, and the histochemical and physical profiles of the resting spore wall, it is suggested that I. hoferi be assigned to a new class within the eumycomycotinid phylum, Mastigomycotina.;Infection of L. ferruginea by I. hoferi was characterized by the presence of creamy-white patches and petechiae on various tissues, especially those of kidneys, heart, and liver. Infection caused a chronic granulomatous tissue response characterized by a pleocellular infiltrate, the nature of which varied among the infected tissue types, and among the naturally- and experimentally-infected host fishes examined. Tissue damage leading to host death was probably caused by pressure, atrophy and subsequent loss of structural and functional integrity of infected tissues, and toxins. Observations made on Oncorhynchus mykiss, experimentally infected by I. hoferi, indicated that the pathophysiological response to infection included progressive anaemia and leucocytopaenia.;I. hoferi was found in 56 of 6759 specimens of L. ferruginea, 1 of 613 specimens of Melanogrammus aeglefinus, but none of the other 1222 fishes representing 5 species sampled from Western North Atlantic waters in 1986 and 1987. The fungus was distributed in a patchy manner with infection prevalence ranging from 0.6% to 10% within the yellowtail flounder population of the Nova Scotian shelf. There was no apparent seasonal cycle in infection prevalence. However, the pathogen appeared to be recruited into L. ferruginea from early summer through to early fall months. |
