Free-living amoebae infecting freshwater and marine fish include those described thus far as agents of fish diseases, associated with other disease conditions and isolated from organs of asymptomatic fish. This survey is based on information from the literature as well as on our own data on strains isolated from freshwater and marine fish. Evidence is provided for diverse fish-infecting amphizoic amoebae. Recent progress in the understanding of the biology of Neoparamoeba spp., agents responsible for significant direct losses in Atlantic salmon and turbot industry, is presented. Specific requirements of diagnostic procedures detecting amoebic infections in fish and taxonomic criteria available for generic and species determination of amphizoic amoebae are analysed. The limits of morphological and non-morphological approaches in species determination are exemplified by Neoparamoeba, Vannella and Platyamoeba spp., which are the most common amoebae isolated from fish gills, Acanthamoeba and Naegleria spp. isolated from various organs of freshwater fish, and by other unique fish isolates of the genera Nuclearia, Thecamoeba and Filamoeba. Advances in molecular characterisation of SSU rRNA genes and phylogenetic analyses based on their sequences are summarised. Attention is particularly given to specific diagnostic tools for fish-infecting amphizoic amoebae and ways for their further development.
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.
This paper sums up the results of light microscopical, ultrastructural and molecular studies of five strains of amoeboid organisms isolated as endocommensals from coelomic fluid of sea urchins, Sphaerechinus granularis (Lamarck), collected in the Adriatic Sea. The organisms are reported as Didymium-like myxogastrids. Of the life-cycle stages, the attached amoeboids, flagellated trophozoites, cysts and biflagellated swarmers are described. Formation of fruiting bodies was not observed. Although phylogenetic analyses of SSU rDNA sequences indicated a close relationship with Hyperamoeba dachnaya, our sea-urchin strains have not been assigned to the genus Hyperamoeba Alexeieff, 1923. The presence of either one or two flagella reported in phylogenetically closely related organisms and mutually distant phylogenetic positions of strains declared as representatives of the genus Hyperamoeba justify our approach. Data obtained in this study may be useful in future analyses of relationships of the genera Didymium, Hyperamoeba, Physarum and Pseudodidymium as well as in higher-order phylogeny of Myxogastrea.
The nematode Philometra rubra (Leidy, 1856) (Philometridae) is redescribed from subgravid females found in the abdominal cavity of the fish Morone saxatilis (Walbaum) from South Carolina, USA in November 2008. The species is characterized by the presence of 14 cephalic papillae arranged in two circles, a relatively long oesophagus with a distinct anterior inflation, and well-developed papilla-like caudal projections. Cephalic papillae of the external circle differ from those in other congeners in that the dorso-lateral and ventro-lateral papillae are large, dome-shaped, whereas the dorso-dorsal and ventro-ventral papillae are small.
Effort was made to identify Naegleria strains isolated from organs of fish, using phylogenetic analyses of SSU rDNA and ITS sequences. Eighteen fish-isolated strains studied enlarged substantially the so far available set of Naegleria strains characterized by both molecular markers. The phylogenetic analyses of separate and concatenated SSU rDNA and ITS sequences revealed phylogenetic relationships of strains under study; however, they failed to solve classification of fish-isolated strains into species. The sequence similarity of strain-representatives of Naegleria species as well as data obtained on intragenomic variation of ITS sequences discouraged the authors from the definition of new species. The results of the present study provide evidence of a need to re-evaluate the current practice of setting boundaries between species of the genus Naegleria. Sequences obtained in this study have been deposited in GenBank with accession numbers DQ768714-DQ768743.
Based on morphological and molecular characterisation, four amoeba strains isolated from organs of freshwater fish were identified as Hartmannella vermiformis Page, 1967. Small subunit rRNA gene sequences of these strains expand the set of corresponding complete and almost complete sequences of this species to twelve. A new species-specific oligonucleotide probe inferred from recently available SSU rRNA gene sequences was designed and successfully tested in tissue lesions produced by one strain of H. vermiformis in experimentally infected fish.
Current records of marine myxozoans from the coast of Africa are limited to the descriptions of 52 species from mostly Senegal, with a few from Tunisia and southern Africa. Between 1998 and 2000 several intertidal fishes from the southern Cape coast of South Africa were examined for the presence of myxozoan infections. Three new species, Ceratomyxa dehoopi sp. n., C. cottoidii sp. n. and C. honckenii sp. n. were identified from the gall bladders of Clinus superciliosus L., C. cottoides Valenciennes and Amblyrhynchotes honckenii (Bloch), respectively. A fourth new species Henneguya clini sp. n. was also identified from the gills and gill arches of C. superciliosus.
A new myxosporean species, Henneguya cynoscioni sp. n., is described from the spotted seatrout, Cynoscion nebulosus (Cuvier) (Sciaenidae) as a causative agent of cardiac henneguyosis. This new myxosporean species is characterized by the morphology of spores and the sequence of SSU rDNA. Examination of 227 spotted seatrout from four South Carolina estuaries in 2008-2010 revealed a 33.5% total prevalence of H. cynoscioni. Henneguya cynoscioni produces lesions in the bulbus arteriosus, its specific site of infection. The severity of lesions and their impact on the bulbus arteriosus is proportional to the number of plasmodial stages developing in this segment of the heart, being most pronounced in host reaction directed against spores liberated from plasmodia.