First record of Trichodina heterodentata (Ciliophora: Trichodinidae) in banded knifefish Gymnotus carapo (Gymnotidae) cultured in Brazil / Primeiro registro de Trichodina heterodentata (Ciliophora: Trichodinidae) em tuvira Gymnotus carapo (Gymnotidae), cultivado no Brasil

The aim of this study was to report the first record of Trichodina heterodentata in banded knifefish Gymnotus carapo. Banded knifefish cultivated in the municipality of Jataí, state of Goiás, in the central western region of Brazil, experienced fish mortality rates of 3-4% per tank. Macroscopic analysis found that fish had lesions on their skin and gills. Smears of the integument and gills were confectioned and air-dried at room temperature and impregnated with silver nitrate to identify the Trichodinidae species causing the lesions. The trichodinid were identified as T. heterodentata, and their characteristics were compared to those from T. heterodentata recorded from other species of host fish. It was observed that the presence of T. heterodentata was associated with inadequate fish management, low water quality, high rates of stocking density, and inadequate nutritional management.

O objetivo deste estudo foi relatar o primeiro registro de Trichodina heterodentata em tuviras Gymnotus carapo. Um cultivo de tuviras no município de Jataí, estado de Goiás, na região Centro-Oeste do Brasil, apresentou taxas de mortalidade de peixes de 3-4% por tanque. A análise macroscópica constatou que os peixes tinham lesões na pele e brânquias. Raspados do tegumento e brânquias foram confeccionadas e secas ao ar à temperatura ambiente e impregnadas com nitrato de prata para identificar as espécies de Trichodinidae causadoras das lesões. Os tricodinídeos foram identificados como T. heterodentata, e suas características foram comparadas com as de T. heterodentata registradas para outras espécies de peixes hospedeiros. Observou-se que a presença de T. heterodentata estava associada ao manejo inadequado dos peixes, baixa qualidade da água, altas taxas de densidade de estocagem e manejo nutricional inadequado.

Seven new species of Urocleidoides (Monogenea: Dactylogyridae) from Brazilian fishes supported by morphological and molecular data.

Seven new species of Urocleidoides from the gills and skin of nine Neotropical fish hosts (Anostomidae, Parodontidae, and Gymnotidae) are described: Urocleidoides digitabulum n. sp. on Leporinus friderici, Leporinus octofasciatus, and Megaleporinus elongatus (Anostomidae); Urocleidoides solarivaginatus n. sp. on L. friderici, L. octofasciatus, and Leporinus striatus (Anostomidae); Urocleidoides falxus n. sp. and Urocleidoides sapucaiensis n. sp. on M. elongatus; Urocleidoides tenuis n. sp. on Apareiodon piracicabae and Apareiodon affinis (Parodontidae); Urocleidoides sinus n. sp. on L. striatus, Schizodon nasutus, and Schizodon intermedius (Anostomidae); and Urocleidoides uncinus n. sp. on Gymnotus sylvius (Gymnotidae). Urocleidoides paradoxus was also found in this study on L. friderici and included in the phylogenetic analysis. Molecular data (partial 28S rDNA and mitochondrial cytochrome oxidase subunit I) were obtained for U. digitabulum n. sp., U. tenuis n. sp., U. sinus n. sp., and U. uncinus n. sp. The identification of Urocleidoides is amended herein to include all taxonomic modifications observed in this genus over time and add new characteristics observed in the species in the present study. Phylogenetic analysis revealed Urocleidoides digitabulum n. sp. and Urocleidoides sinus n. sp. (parasites of anostomids) closely related in the tree topologies. Furthermore, the new species described herein parasitized phylogenetically distant host species (Characiformes and Gymnotiformes), suggesting the effect of the dynamic process of ecological fitting.

Parasitism by Clinostomum marginatum (Clinostomidae) in neotropical electric fish (Gymnotiformes) in the Brazilian Amazon

Gymnotiformes are currently recognized as electric fish, the vast majority of which emit low power electrical discharges. Clinostomum trematodes have been the subject of numerous investigations in several host species due to the ability of metacercariae of this genus to infect the muscles, fins and internal organs of fish. The present study aimed to record, for the first time, the occurrence of parasitism by Clinostomum marginatum in Gymnotiformes from the natural environments of two tributaries of the Amazon River in the Brazilian Amazon. Two specimens of Gymnotus coropinae, ten specimens of Brachyhypopomus brevirostris, two specimens of Gymnorhamphycthys petiti and one specimen of Microsternarchus bilineatus were captured. Infection with C. marginatum was identified in the form of 12 encysted metacercariae in the epidermis, with a prevalence of 0.1%, a mean infection intensity of 12/fish and an average abundance of 1.2. This is the first record of parasitism by the C. marginatum in South American Gymnotiformes of the B. brevirostris species.

Description of two new species of allocreadiid trematodes (Digenea: Allocreadiidae) in middle American freshwater fishes using an integrative taxonomy approach.

Integrative taxonomy uses several sources of information to establish more robust species delimitation criteria. In this study, we followed that approach to describe two new species of allocreadiid trematodes from freshwater fish distributed in locations across Middle America. The new species were first recognized by using sequences of the domains D1-D3 of the ribosomal 28S rRNA gene and then, morphological data (light and scanning electron microscopy (SEM)), host association, and geographical distribution were considered as additional sources of information to complement the species delimitation and description. Auriculostoma tica n. sp. was found in the intestine of Gymnotus maculosus Albert and Miller in Costa Rica, while Wallinia anindoi n. sp. was found in the intestine of Astyanax aeneus (Günther) in Oaxaca and Chiapas, Mexico, as well as in a location of Guatemala. A phylogenetic analysis combining newly generated sequences of the two new species along with those available for other allocreadiids in GenBank, revealed that isolates of each species are reciprocally monophyletic, and also their interrelationships: Au. tica n. sp. is a sister taxon of Auriculostoma totonacapanensis Razo-Mendivil et al., 2014, and W. anindoi n. sp. is a sister taxon of Wallinia brasiliensis Dias, et al., 2018. Genetic distances for the 28S rRNA gene were estimated among the American species of allocreadiids and further supported the validity of the new species.

Morphological and morphometric features of nematode-cysts in Gymnotus inaequilabiatus liver in the Brazilian Pantanal.

The aim of this study was to determine the morphometric measures and morphological aspects of nematode-cysts in Gymnotus inaequilabiatus, and the presence of melanomacrophage centers (MMCs) associated with the periphery of cysts and in the liver parenchyma. Adult specimens, 34 female (123.1 ± 43.9g) and 45 male (135.5 ± 43.4g), from Paraguay River, Corumbá, Brazil, were used. The number of nematode-cysts was determined in 79 livers and 25 of them randomly selected for histopathological analysis and morphometric measures of nematode-cysts (mean diameter, thickness of collagen layer, and cyst-wall layer). The percentage of cysts with MMCs on the periphery and density in the liver parenchyma was estimated. The average number of macroscopic cysts was of 48.7 ± 2.78. Granulomatous reaction was observed surrounding the cysts. Diameter, collagen layer and cyst-wall measurements were 293.0 ± 75.18 (µm), 17.72 ± 6.01 (µm) and 12.21 ± 9.51 (µm), respectively. The number of nematode-cysts was correlated with hepatosomatic index, (r=0.26, P<0.05). Collagen layer was correlated with cyst diameter (r=0.62, P<0.01). Pericystic and parenchymatous MMCs were moderately (r=0.48) and highly (r=0.90) correlated with nematode-cysts number. Morphological characteristics of hepatic tissue and cysts-nematodes measures suggest that G. inaequilabiatus acts as a paratenic host to nematodes in the larval stage.

Morphological and morphometric features of nematode-cysts in Gymnotus inaequilabiatus liver in the Brazilian Pantanal / Características morfológicas e morfométricas de cistos de nematódeos em fígado de Gymnotus inaequilabiatus no Pantanal brasileiro

Abstract The aim of this study was to determine the morphometric measures and morphological aspects of nematode-cysts in Gymnotus inaequilabiatus, and the presence of melanomacrophage centers (MMCs) associated with the periphery of cysts and in the liver parenchyma. Adult specimens, 34 female (123.1 ± 43.9g) and 45 male (135.5 ± 43.4g), from Paraguay River, Corumbá, Brazil, were used. The number of nematode-cysts was determined in 79 livers and 25 of them randomly selected for histopathological analysis and morphometric measures of nematode-cysts (mean diameter, thickness of collagen layer, and cyst-wall layer). The percentage of cysts with MMCs on the periphery and density in the liver parenchyma was estimated. The average number of macroscopic cysts was of 48.7 ± 2.78. Granulomatous reaction was observed surrounding the cysts. Diameter, collagen layer and cyst-wall measurements were 293.0 ± 75.18 (µm), 17.72 ± 6.01 (µm) and 12.21 ± 9.51 (µm), respectively. The number of nematode-cysts was correlated with hepatosomatic index, (r=0.26, P<0.05). Collagen layer was correlated with cyst diameter (r=0.62, P<0.01). Pericystic and parenchymatous MMCs were moderately (r=0.48) and highly (r=0.90) correlated with nematode-cysts number. Morphological characteristics of hepatic tissue and cysts-nematodes measures suggest that G. inaequilabiatus acts as a paratenic host to nematodes in the larval stage.

Resumo O objetivo deste estudo foi determinar as características morfológicas e morfométricas de cistos de nematodas em fígado de Gymnotus inaequilabiatus, e a presença de centros de melanomacrófagos (CMMs) pericísticos e no parênquima hepático. Espécimes adultos, 34 fêmeas (123,1 ± 43,9 g) e 45 machos (135,5 ± 43,4g), provenientes do Rio Paraguai, Corumbá, Brasil foram utilizados. Os cistos foram quantificados em 79 fígados. Em 25 fígados foi realizada a análise histopatológica e morfometria dos cistos (diâmetro, espessura da camada de colágeno e da parede). Estimou-se a porcentagem de cistos com CMMs periférico e a densidade de CMMs no parênquima. A média de cistos macroscópicos foi de 48,7 ± 2,78. Observou-se reação granulomatosa pericística. O diâmetro, a espessura da camada de colágeno e da parede do cisto foi de 293,0 ± 75,18 (µm), 17,72 ± 6,01 (µm) e 12,21 ± 9,51 (µm), respectivamente. O número de cistos foi associado ao índice hepatossomático, (r=0,26, P <0,05). A camada de colágeno correlacionou-se com o diâmetro do cisto (r=0,62, P <0,01). CMMs pericísticos e do parênquima apresentaram correlação moderada (r=0,48) e alta (r=0,90) com o número de cistos, respectivamente. As características morfológicas do tecido hepático e a morfometria dos cistos de nematodas sugerem que G. inaequilabiatus atua como hospedeiro paratênico para larvas de nematodas.

Liver of the fish Gymnotus inaequilabiatus and nematode larvae infection: Histochemical features and expression of proliferative cell nuclear antigen.

Histopathological lesions due to third-larval stage of nematode Brevimulticaecum sp. within the liver of a subpopulation of 31 Gymnotus inaequilabiatus from the Pantanal Region (Brazil) were studied with histochemical and immunohistochemical methods. In 93.5% of fish, livers harboured nematode larvae and the intensity of infection ranged from 8 to 293. In livers with highest number of larvae, the hepatic tissue was occupied primarily by the nematodes. Each larva was encircled by focal inflammatory granulomatous reaction. Within the thickness of the granuloma, three concentric layers were recognized: an inner layer of densely packed epithelioid cells, a middle layer of mast cells (MCs) entrapped in a thin fibroblast-connective mesh and an outer layer of fibrous connective tissue with fibroblasts. Epithelioid cells and fibroblasts within the thickness of the granuloma wall were positive for proliferative cell nuclear antigen (PCNA). Moreover, several hepatocytes in infected liver were immunoreactive to PCNA. Occurrence of rodlet cells and MCs in parenchyma, in close proximity to the encysted nematode larvae and near the blood vessel of infected liver, was observed. Macrophage aggregates (MAs) were numerous within the granulomas and scattered in parenchyma of the infected liver. High quantity of haemosiderin was encountered in MAs and hepatocytes of infected liver.

Nematode infection in liver of the fish Gymnotus inaequilabiatus (Gymnotiformes: Gymnotidae) from the Pantanal Region in Brazil: pathobiology and inflammatory response.

BACKGROUND: A survey on endoparasitic helminths from freshwater fishes in the Pantanal Region (Mato Grosso do Sul, Brazil) revealed the occurrence of third-larval stage of the nematode Brevimulticaecum sp. (Heterocheilidae) in most organs of Gymnotus inaequilabiatus (Gymnotidae) also known by the local name tuvira. The aim of the present study was to examine Brevimulticaecum sp.-infected tuvira liver at the ultrastructural level and clarify the nature of granulomas and the cellular elements involved in the immune response to nematode larvae. METHODS: Thirty-eight adult specimens of tuvira from Porto Morrinho, were acquired in January and March 2016. Infected and uninfected liver tissues were fixed and prepared for histological and ultrastructure investigations. RESULTS: The prevalence of infection of tuvira liver by the nematode larvae was 95 %, with an intensity of infection ranging from 4 to 343 larvae (mean ± SD: 55.31 ± 73.94 larvae per liver). In livers with high numbers of nematode larvae, almost entire hepatic tissue was occupied by the parasites. Hepatocytes showed slight to mild degenerative changes and accumulation of pigments. Parasite larvae were surrounded by round to oval granulomas, the result of focal host tissue response to the infection. Each granuloma was typically formed by three concentric layers: an outer layer of fibrous connective tissue with thin elongated fibroblasts; a middle layer of mast cells entrapped in a thin fibroblast-connective mesh; and an inner layer of densely packed epithelioid cells, displaying numerous desmosomes between each other. Numerous macrophage aggregates occurred in the granulomas and in the parenchyma. CONCLUSIONS: Our results in tuvira showed that the larvae were efficiently sequestered within the granulomas, most of the inflammatory components were confined within the thickness of the granuloma, and the parenchyma was relatively free of immune cells and without fibrosis. Presumably this focal encapsulation of the parasites permits uninfected portions of liver to maintain its functions and allows the survival of the host.

Lymphocytic meningoencephalomyelitis associated with Myxobolus sp. (Bivalvulidae: Myxozoa) infection in the Amazonian fish Eigenmannia sp. (Sternopygidae: Gymnotiformes) / Meningoencefalomielite linfocitária associada à infecção por Myxobolus sp. (Bivalvulidae:Myxozoa) em peixe amazônico Eigenmannia sp. (Sternopygidae: Gymnotiformes)

Abstract The genus Myxobolus, parasites that infect fishes, which cause myxobolosis, includes spore organisms belonging to the phylum Myxozoa and represents approximately 36% of all species described for the entire phylum. This study describes lymphocytic meningoencephalomyelitis associated with Myxobolus sp. infection in the brain and spinal cord (the central nervous system, CNS) of Eigenmannia sp., from the Amazon estuary region, in the Administrative District of Outeiro (DAOUT), Belém, Pará, Brazil. In May and June 2015, 40 Eigenmannia sp. specimens were captured from this region and examined. The fish were anesthetized, slaughtered and dissected for sexing (gonad evaluation) and studying parasites and cysts; after diagnosing the presence of the myxozoans using a light microscope, small fragments of the brain and spinal cord were removed for histological processing and Hematoxylin-Eosin and Ziehl-Neelsen staining. Histopathological analysis of the brain and spinal cord, based on histological sections stained with Hematoxylin-Eosin, pronounced and diffuse edema in these tissues, and congestion, degeneration, and focal necrosis of the cerebral cortex. The present study describes lymphocytic meningoencephalomyelitis associated with infection by Myxobolus sp. in the central nervous system of Eigenmannia sp.

Resumo O gênero Myxobolus é composto por parasitas esporais que podem infectar peixes e causar a “myxobolose”. São organismos pertencentes ao filo Myxozoa e representam cerca de 36% do total de espécies descritas para todo o Filo. Este estudo descreve meningoencefalomielite linfocitária, associada à infecção por Myxobolus sp. no cérebro e medula espinhal (SNC) de Eigenmannia sp, oriundo de região estuarina amazônica, no Distrito Administrativo de Outeiro (DAOUT), município de Belém, Pará, Brasil. Foram capturados e examinados 40 espécimes de Eigenmannia sp. entre os meses de maio e junho de 2015. Os peixes foram anestesiados, abatidos e dissecados para sexagem (avaliação das gônadas) e pesquisa de parasitos e cistos. Após o diagnóstico da presença dos mixosporidios, utilizando-se microscópio de luz, pequenos fragmentos do cérebro e da medula espinal foram removidos para processamento histológico e coloração por Hematoxilina-Eosina e coloração especial em Ziehl-Neelsen. A análise histopatológica do cérebro e da medula espinhal, com base em cortes histológicos corados com Hematoxilina-Eosina, mostrou edema difuso nesses tecidos, e congestão, degeneração e necrose focal do córtex cerebral. O presente estudo descreve meningoencefalomielite linfocítica, associada à infecção por Myxobolus sp., no sistema nervoso central de Eigenmannia sp.

Lymphocytic meningoencephalomyelitis associated with Myxobolus sp. (Bivalvulidae: Myxozoa) infection in the Amazonian fish Eigenmannia sp. (Sternopygidae: Gymnotiformes).

The genus Myxobolus, parasites that infect fishes, which cause myxobolosis, includes spore organisms belonging to the phylum Myxozoa and represents approximately 36% of all species described for the entire phylum. This study describes lymphocytic meningoencephalomyelitis associated with Myxobolus sp. infection in the brain and spinal cord (the central nervous system, CNS) of Eigenmannia sp., from the Amazon estuary region, in the Administrative District of Outeiro (DAOUT), Belém, Pará, Brazil. In May and June 2015, 40 Eigenmannia sp. specimens were captured from this region and examined. The fish were anesthetized, slaughtered and dissected for sexing (gonad evaluation) and studying parasites and cysts; after diagnosing the presence of the myxozoans using a light microscope, small fragments of the brain and spinal cord were removed for histological processing and Hematoxylin-Eosin and Ziehl-Neelsen staining. Histopathological analysis of the brain and spinal cord, based on histological sections stained with Hematoxylin-Eosin, pronounced and diffuse edema in these tissues, and congestion, degeneration, and focal necrosis of the cerebral cortex. The present study describes lymphocytic meningoencephalomyelitis associated with infection by Myxobolus sp. in the central nervous system of Eigenmannia sp.

First record of Chilodonella hexasticha (Ciliophora: Chilodonellidae) in Brazilian cultured fish: a morphological and pathological assessment.

Chilodonelids are small ciliated protozoans found worldwide and can be dangerous in culture conditions. This study presents morphometric data on the ciliate Chilodonella that is found in cultured Nile tilapia (Oreochromis niloticus), native bait fish tuvira (Gymnotus aff. inaequilabiatus) and native pacu (Piaractus mesopotamicus) and includes a histopathological assessment of the changes that occur in the pacu. For parasitic diagnosis, skin and gill samples were scraped onto slides, dried at room temperature, stained with Giemsa or impregnated with silver nitrate, and the measurements were obtained from photomicrographs. In the diseased pacu, the first gill arch was collected and fixed in a 10% buffered formalin solution for histopathological analysis. Parasite specimens from the different collection sites were identified morphologically as C. hexasticha Kiernik (1909). Diseased fish exhibited depigmentation, skin ulceration, scale loss, excessive mucus production and gill lesions. Histopathological analysis of pacu gills displayed epithelial proliferation with mononuclear inflammatory infiltrate, hemorrhages, and scattering necrosis. In Brazilian-farmed fish this is the first record of C. hexasticha, which has great pathogenic potential in cultured freshwater species. In addition, two new hosts are presented.

Two new species of Parspina Pearse, 1920 (Digenea: Cryptogonimidae) from freshwater fishes (Gymnotiformes) of the Paraná River basin in Argentina.

Two new species of the cryptogonimid genus Parspina Pearse, 1920 are described from gymnotiform fishes of the Paraná River basin, P. carapo n. sp. from the banded knifefish Gymnotus carapo Linnaeus and P. virescens n. sp. from the glass knifefish Eigenmannia virescens (Valenciennes). Parspina carapo differs from P. virescens in the number of oral spines (32-39 vs 30-33) and their length (28-47 vs 16-28 µm), the distribution of tegumental spines and their anchorage, the types of sensory papillae on the body surface (three vs two types), the extent of body length posterior to the caeca (5 vs 13% of the total body length), the dimensions of the pars prostatica (52 × 34 vs 24 × 10 µm), and in the absence of a gonotyl (vs presence). Both P. carapo and P. virescens differ from P. bagre Pearse, 1920 and P. argentinensis (Szidat, 1954) in the number of oral spines (20-21 and 21-28 in the latter pair) and their length (28-32 and 35-60 µm), and in total body length. Additionally, the two new species differ from P. argentinensis in the arrangement of the vitelline follicles (one continuous band vs two groups on each side of the body) and in having a smaller pars prostatica (149 × 49 µm in the latter). Parspina carapo is the fifth intestinal helminth found in G. carapo, and P. virescens is the first found in E. virescens.

First record of Trypanosoma sp. (Protozoa: Kinetoplastida) in tuvira (Gymnotus aff. inaequilabiatus) in the Pantanal wetland, Mato Grosso do Sul State, Brazil.

The blood infection by Trypanosoma sp. in tuvira (Gymnotus aff. inaequilabiatus) from the Pantanal wetland was reported in this study. Ten fish from the Paraguay River in the Pantanal were evaluated for the presence of hemoflagellates. Trypomastigotes of Trypanosoma sp. were observed in blood smears from three fish (30% prevalence) and some forms were seen to be undergoing division. Using the diagnostic methods of fresh examination and blood centrifugation in hematocrit capillary tubes, the prevalence rate was 80%. This is the first report of Trypanosoma sp. in tuvira in Brazil.

First record of Trypanosoma sp. (Protozoa: Kinetoplastida) in tuvira (Gymnotus aff. inaequilabiatus) in the Pantanal wetland, Mato Grosso do Sul State, Brazil / Primeiro registro de Trypanosoma sp. (Protozoa: Kinetoplastida) em tuvira (Gymnotus aff. inaequilabiatus) no Pantanal, Mato Grosso do Sul, Brasil

The blood infection by Trypanosoma sp. in tuvira (Gymnotus aff. inaequilabiatus) from the Pantanal wetland was reported in this study. Ten fish from the Paraguay River in the Pantanal were evaluated for the presence of hemoflagellates. Trypomastigotes of Trypanosoma sp. were observed in blood smears from three fish (30 percent prevalence) and some forms were seen to be undergoing division. Using the diagnostic methods of fresh examination and blood centrifugation in hematocrit capillary tubes, the prevalence rate was 80 percent. This is the first report of Trypanosoma sp. in tuvira in Brazil.

O objetivo do presente estudo foi reportar a infecção por Trypanosoma sp. em tuviras (Gymnotus aff. inaequilabiatus) oriundas do Pantanal Sul-mato-grossense, Brasil. Dez peixes provenientes do rio Paraguai, Pantanal Sul-mato-grossense, foram avaliados quanto à presença de hemoflagelados. Tripomastigotas de Trypanosoma sp. foram observados nas extensões sanguíneas de três peixes (30 por cento de prevalência), e algumas formas encontravam-se em divisão. Por meio do exame a fresco e da centrifugação do sangue em capilar de hematócrito como métodos para diagnóstico, a taxa de prevalência foi de 80 por cento. Esse é o primeiro relato de Trypanosoma sp. em tuviras no Brasil.

Five new species of Urocleidoides (Monogenoidea) (Mizelle and Price 1964) Kritsky, Thatcher, and Boeger, 1986, parasitizing the gills of Panamanian freshwater fishes.

During an investigation of gill monogenoidean parasites from freshwater fishes in central Panama, 5 new species of Urocleidoides (sensu stricto) were found: Urocleidoides cultellus n. sp., Urocleidoides visiofortatus n. sp., and Urocleidoides advenai n. sp. from the gymnotiform Brachyhypopomus occidentalis (Hypopomidae); Urocleidoides neotropicalis n. sp. and Urocleidoides piriatiu n. sp. from the characiforms Saccodon dariensis (Parodontidae) and Ctenolucius beani (Ctenoluciidae), respectively. Our findings represent the first known species of Urocleidoides from these fishes in Central America and demonstrate that they are morphologically linked to their South American congeners.

Neotropical Monogenoidea. 52. Diechodactylus joaberi n. g., n. sp. from the banded knifefish Gymnotus carapo (Gymnotiformes: Gymnotidae) in southeastern Brazil.

Diechodactylus joaberi n. g., n. sp. is described from the body surface of the banded knifefish Gymnotus carapo L. (Gymnotiformes: Gymnotidae) from southeastern Brazil. The new genus is proposed to accommodate species with five pairs of hooks in anterior bilateral clusters on the haptor, three pairs of hooks in a single cluster on the posterior margin of the haptor, sclerites R1 associated with the superficial bar, and confluent intestinal caeca. The presence of five pairs of hooks in two bilateral clusters anterior in the haptor permits the differentiation of species of Diechodactylus from species of all known genera of the Gyrodactylidae. The genus is likely a member of a clade of the Gyrodactylidae comprising genera with a similar hook distribution.

[The symbiotic microflora associated with the tegument of proteocephalidean cestodes and the intestines of their fish hosts].

The indigenous symbiotic microflora associated with the tegument of proteocephalidean cestodes and the intestines of their fish hosts has been investigated in morphological and ecological aspects. The indigenous microflora associated with the cestode tegument consists of the nannobacteria population, which was present obligatorily on the surface of tegument, and the "deep microflora". The deep microflora associates with some few species of parasites only. Each individual host-parasite micro-biocenosis includes specific indigenous symbiotic microorganisms, with the differing microfloras of host intestine and parasite. Physiology, biochemistry and/or diet of hosts apparently influence on the symbiotic microflora's structure of parasites. The least bacteria abundance and diversity of their morphotypes were observed in the parasites from baby fishes. The diversity and abundance of bacteria were increased with the fish host ageing and the formation of the definitive structure of its intestine. It is an evidence of the gradual invading of the intestinal parasites (cestodes) tegument by bacterial cells. The invading is realized on the base of the microflora that was present in the food of fish host. The symbiotic microflora has specific morphological features, can regulate the homeostasis of the cestodes and fish hosts and also can maintain equilibrium of alimentary and immune interrelations in the host-parasite system.

Parasitism of Cichlasoma paranaense Kullander, 1983 and Gymnotus carapo Linnaeus, 1814 by Clinostomum complanatum (Rudolphi, 1814) metacercariae in the Taquari river.

The infection, known as yellow spot disease, produced by metacercariae of Clinostomum spp. was studied in fishes of the Taquari river, located in Jataizinho, Paraná State, Brazil. A total of 1,582 specimens, belonging to 36 species, were collected between March 1999 and April 2001. Yellow spot disease was observed only in Gymnotus carapo Linnaeus, 1814 (Gymnotiformes, Gymnotidae) and Cichlasoma paranaense Kullander, 1983 (Perciformes, Cichlidae). This parasitism was generated by metacercariae of Clinostomum complanatum (Rudolphi, 1814) (Digenea, Clinostomidae). Among the 88 specimens of G. carapo examined, 7 (prevalence = 8%) had cysts of the parasite. Four of them were captured in July 1999 and three in October 1999. In the other months, no specimen found was infected. Using relative condition factor (Kn) analysis, it was determined that both infected and non-infected specimens had a total weight equal to the theoretically expected value for each total length (Kn = 1.0). Among 56 individuals of Cichlasoma paranaense, 6 (prevalence = 10.7%) had between 1 and 27 metacercariae of C. complanatum (mean intensity of infection = 9.3 +/- 9.6). In March 1999 and April of both 2000 and 2001, the specimens examined were not infected. The infected fish had a total weight higher than the expected value (Kn > 1.0), while the non-infected fish had a weight equal to the expected value (Kn = 1.0).

Parasitism of Cichlasoma paranaense Kullander, 1983 and Gymnotus carapo Linnaeus, 1814 by Clinostomum complanatum (Rudolphi, 1814) Metacercariae in the Taquari river

Estudou-se a infecção por metacercárias de Clinostomum spp., conhecida como doença das manchas amarelas, em peixes do rio Taquari, localizado no município de Jataizinho, Paraná, Brasil. Um total de 1.582 espécimes pertencentes a 36 espécies foram capturados entre março de 1999 e abril de 2001. As manchas amarelas foram observadas apenas em Gymnotus carapo Linnaeus, 1814 (Gymnotiformes, Gymnotidae) e Cichlasoma paranaense Kullander, 1983 (Perciformes, Cichlidae). Esse parasitismo foi produzido por larvas de Clinostomum complanatum (Rudolphi, 1814) (Digenea, Clinostomidae), na fase de metacercária. Dentre os 88 espécimes de G. carapo examinados, 7 (prevalência = 8%) tinham cistos do parasita. Destes, 4 foram capturados em julho de 1999, quando foi observada a mais alta intensidade de infecção, e 3 em outubro de 1999. Nos outros meses, nenhum espécime encontrava-se infectado. Analisando o fator de condição relativo (Kn) foi possível determinar que tanto os exemplares parasitados como os não parasitados estavam com o peso igual ao teoricamente esperado para cada comprimento (Kn = 1,0). Entre os 56 indivíduos de Cichlasoma paranaense, 6 (prevalência = 10,7%) apresentavam entre 1 e 27 metacercárias de C. complanatum (intensidade média de infecção = 9,3 ± 9,6). A mais alta intensidade de infecção foi registrada em janeiro de 2000. Em março de 1999 e em abril de 2000 e de 2001, nenhum dos espécimes examinados estava infectado. Os peixes parasitados encontravam-se com o peso total acima do esperado (Kn > 1,0), enquanto os não parasitados apresentaram peso total igual ao esperado (Kn = 1,0).

Two new species of Nomimoscolex (Cestoda: Proteocephalidea, Monticelliidae) from Gymnotus carapo (Pisces: Gymnotiformes) in Argentina.

Nomimoscolex guillermoi n. sp. and N. dechambrieri n. sp. are described from the gymnotiform fish Gymnotus carapo from Argentina. The new species are placed into Nomimoscolex based on the cortical position of the vitelline follicles, and medullary position of the testes, ovary, and uterus. Both species were compared to the 13 species considered valid in the genus. The combination of features distinguishing N. guillermoi from N. dechambrieri is (1) the position of the vagina to cirrus pouch (anterior or posterior vs always anterior respectively), (2) the total number of testes (41-85 vs 108-130 respectively), (3) the distribution of the vitelline follicles (arranged in dorso-lateral and ventro-lateral bands vs lateral bands respectively), (4) the length of the uteroduct (ending 58% vs 35% from posterior margin of mature proglottis respectively), and (5) the presence of gland cells in the scolex (unicellular glands in the apical region and the external margin of suckers vs the presence of unicellular glands in the apex and other grouped in a cluster medially to the suckers respectively).