Three amoeba species were isolated from 3 out of 193 farmed tilapias, Oreochromis niloticus (L.), screened for the presence of free-living amoebae in parenchymatous organs. Hartmannella vermiformis Page, 1967 and Rosculus ithacus Hawes, 1963 were isolated from the kidney tissue. The third strain isolated from the liver shared morphological features of Mayorella and Platyamoeha spp. and therefore its taxonomic position has not been determined as yet. Pathogenicity of cloned strain of H. vermiformis was proved in two fish hosts.
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.
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.
Four strains of non-encysting amoebae were isolated from organs of freshwater fishes and characterized using light and electron microscope. Morphology of three clonal strains was consistent with amoebae which had already been described from water habitats. Two strains, one isolated from kidney tissue of common goldfish, Carassius auratus (Linnaeus, 1758), and the second one from brain of chub, Leuciscus cephalus Linnaeus, 1758, were identified with Vannella platypodia (Gläser, 1912) Page, 1976. Both strains were identical, except for the length of glycostyles. The strain isolated from the liver of perch, Perea fluviatilis (Linnaeus, 1758), was assigned to the genus Vexillifera Schaeffer, 1926 as Vexillifera expectata sp. n. The taxonomic position of the fourth non-encysting strain could not be safely established, although it shares some trophic cell structures with protostelids (Protostelia, Eumycetozoea). We present its detailed description here also to demonstrate that amoeba stages of this type of organisms are capable to infect fishes.