Ninety four aquarium fishes were screened for the presence of amoebae in their internal organs. Five specimens of Ca-rassius auratus (L.) and one specimen of Xiphophorus hetleri Heckel were positive. Of the three strains which were isolated from C. auratus, successfully cloned and cultivated, one was identified as Vannella platypodia (Gläser, 1912) Page, 1976 and two strains as Rosculus ithacus Hawes, 1963. Both species are reported for the first time from organs of fish. None of them could be identified with the amoeba-like agent of goldfish granulomas described here.
The microsporidian Kabatana arthuri (Lom, Dyková et Shaharom, 1990) induced severe regressive changes in trunk muscles of Pangasius sutchi (Fowler) from Thailand. Necrotic changes developed in muscle fibres around the developmental stages and on the periphery of giant aggregates of spores. The main feature of the host defence reaction was the phagocytic activity of macrophages. Inflammatory reaction was only exceptionally observed. Spore-laden macrophages were found in various tissues and organs; their infiltration in epidermis including its outermost layers may effectively enhance the spread of infection while the hosts still live.
Four myxosporean species were found on the gills of Ictiobus bubalus from Illinois (USA). Myxobolus endovasus (Davis, 1947) Grinham et Cone, 1990 is revised. Three new species are recorded. Myxobolus enoblei sp. n. has spores ovoid in frontal view, 14.3 x 13 pm in size. Myxobolus morrisonae sp. n. has spores subcircular in frontal view, 10 x 9.5 pm in size; the surface of shell valves appears hairy when studied by SEM. Triangula illinoisensis sp. n. has spores rounded semicircular in frontal view, 10.2 x 12.8 pm in size. Triangula illinoisensis is the fourth species of its genus to be described from fishes.
Two myxosporean species, Zschokkella pleomorpha Lom et Dyková, 1995 (Zp) and Ortholinea fluviatilis Lom et Dyková, 1995 (Of) from the kidney of Tetraodon fluviatilis were studied by transmission electron microscope. Coelozoic sporogonie plasmodia of both species use pseudopodia-like projections for attachment to the epithelial cells of renal tubules. These projections either attach to host microvilli forming an interface reminiscent of septate junction (Zp) or are embedded into the epithelial cell surface (Of) or are inserted into gaps between epithelial cells (Zp, Of). Zp produces spores only by direct division of generative cells while in Of pansporoblasts prevail over direct division of generative cells. Sporogonie plasmodia of Zp greatly differ in size and in the variety of cytoplasmic constituents. A special feature in capsulogenesis is a transient envelope encasing the capsular primordium; there are fine fibres on the surface of the nascent filament spaced at 11 nm. In Of, vegetative nuclei of the plasmodium adhere to generative cells in a way reminding of sporoplasmic plasmodium of actinospores. In Of plasmodia, several unusual cytoplasmic structures were observed (membrane bound bodies with fuzzy radial contents or with a central dense inclusion, and endoplasmic reticulum cistemae forming a scalloped network). Of may also form intracellular coelozoic sporogonie plasmodia in the epithelial cells of renal tubules; these stages do not seem to constitute an important part of the life cycle.