Occurrence of Loma cf. salmonae in brook, brown and rainbow trout from Buford Trout Hatchery, Georgia, USA

During a 6 mo study of moribund trout from Buford hatchery, Buford, Georgia , USA, a Loma cf. salmonae microsporidian parasite was studied in the gills of brook trout Salvelinus fontinalis, brown trout Salmo trutta, and rainbo w trout Oncorhynchus mykiss. This parasite was morphologically similar to L . salmonae and L. fontinalis but differed in spore size. Scanning and trans mission electron microscopy demonstrated that xenomas were embedded in gill filaments. Transmission electron micrographs prepared from fresh tissue sh owed mature spores with 12 to 15 turns of their polar tube. Spore diameters for the Georgia strain from formalin-fixed gill tissues measured 3.5 (SD /- 0.1) by 1.8 (SD +/- 0.1) Fun. Electron micrographs of formalin-fixed, de paraffinized tissues of rainbow trout from Pennsylvania and West Virginia s how spores with a diameter of 3.5 (+/-0.2) by 1.7 (+/-0.1) mu m and 3.4 (+/ -0.2) by 1.8 (+/-0.1) pm, respectively. Transmission electron micrographs o f spores from Pennsylvania and West Virginia show that mature spores from b oth states had 13 to 15 turns of their polar tubes. Measurements from trans mission electron micrographs prepared from alcohol-fixed tissues from Virgi nia fish contained spores with a diameter of 3.0 (+/-0.3) by 1.1 (+/-0.3) m u m and 12 to 15 turns of their polar tubes. These measurements are consist ent with L, salmonae and therefore suggest that the parasite is present on the east coast of the United States. During the height of the Georgia epizo otic, the percentage of fish with observed xenomas reached 62.2% (N = 87), and the highest number of xenomas counted per 10 gill filaments was 133 (N = 87). The microsporidian epizootic occurred either during the autumn month s or when intake river water quality reached combined iron-manganese concen trations as high as 1.01 (mean 0.44, SD +/- 0.42) mg(-1).