A new species of Tiddergasilus Marques & Boeger, 2018 (Copepoda: Ergasilidae) from the gills of Astyanax lacustris (Lütken) (Osteichthyes: Characidae) in Brazil.

A new parasitic copepod, Tiddergasilus bipartitus n. sp. (Copepoda, Ergasilidae), is described herein based on three adult females found attached to the gills of the yellow-tail lambari Astyanax lacustris (Lütken), sampled in Pardo River, municipality of Botucatu, São Paulo State, Brazil. Tiddergasilus bipartitus n. sp. was recognized as a new member of the monotypic genus Tiddergasilus Marques & Boeger, 2018 by having: antennule 6-segmented; maxillary basis armed with 2 terminal teeth and ornamented with multiple spinules; second and third leg both with endopod 3-segmented. The new copepod can be distinguished from its congener, Tiddergasilus iheringi (Tidd, 1942), by the morphology of the antennal claw, number of somites/segments in abdomen and fourth leg, and by the ornamentation of the first leg. This report expands the geographic distribution and diversity of fish species parasitized with Tiddergasilus spp. in Brazil. Moreover, it also represents the first report of an ergasilid species in the Pardo River. A list of diagnostic features for the Brazilian species of Ergasilus von Nordmann, 1832 is provided herein, in order to aid comparisons with the species of this complex genus.

Myxobolus spp. (Cnidaria: Myxobolidae) in the circulating blood of fishes from Goiás and Mato Grosso States, Brazil: case report / Myxobolus spp. (Cnidaria: Myxobolidae) no sangue circulante de peixes dos estados de Goiás e Mato Grosso, Brasil: relato de caso

Myxosporidiosis is an infectious disease caused by myxozoans of the Phylum Cnidaria, Class Myxosporea, and Order Bivalvulida, considered a common parasite in fresh and saltwater fishes that parasitize many organs, especially gills. In the present study, 49 specimens of fishes belonging to eight genera: Tetragonopterus, Leporinus, Myleus, Pirinampus, Rhapiodon, Pygocentrus, Ageneiosus, and Serrasalmus were collected and blood smears were made, fixed with absolute methanol, and stained with Giemsa 10% to survey hemoparasites. However, myxospores were found in the circulating blood of five (10.20%) fishes belonging to genus Tetragonopterus, Myleus, and Pygocentrus. Two morphological types of Myxobolus spp. were identified in all the five fish specimens analyzed. Usually, investigations on myxozoans in fish are carried out with the search for plasmodia or cysts in the fish organs and observation of the cavity of organs. Nevertheless, this study highlights the importance of also examining the blood of these animals, since these parasites can cause severe pathogenic diseases in fish. Thus, the blood analyses can proportionate preventive sanitary control for commercial fish avoiding economic loss.

A mixosporidiose é considerada uma doença infecciosa causada por mixozoários pertentences ao Filo Cnidaria, Classe Myxosporea e Ordem Bivalvulida, considerados parasitos comuns de peixes de água doce e salgada, parasitando vários órgãos, principalmente as brânquias. No presente estudo, 49 espécimes de peixes pertencentes a oito gêneros: Tetragonopterus, Leporinus, Myleus, Pirinampus, Rhapiodon, Pygocentrus, Ageneiosus and Serrasalmus foram coletados e extensões sanguíneas foram feitas com a finalidade de encontrar hemoparasitos. Entretanto, mixoesporos foram observados em cinco (10.20%) espécimes de peixes, pertencentes aos gêneros Tetragonopterus, Myleus e Pygocentrus. Dois morfotipos de Myxobolus spp. foram identificados parasitando esses peixes. Normalmente, as investigações sobre mixozoários em peixes é realizada com a procura de plasmódios ou cistos nos órgãos dos peixes e observação da cavidade de órgãos. Porém, esse trabalho ressalta a importância de se examinar também o sangue desses animais, já que esses parasitos podem ocasionar patogenias severas em peixes. Sendo assim, a análise sanguínea pode proporcionar controle sanatório preventivo para peixes comerciais e evitar perdas econômicas.

Cryptosporidium abrahamseni n. sp. (Apicomplexa: Cryptosporidiiae) from red-eye tetra (Moenkhausia sanctaefilomenae).

The morphological, biological, and molecular characterisation of Cryptosporidium piscine genotype 7 from red-eye tetras (Moenkhausia sanctaefilomenae) are described, and the species name Cryptosporidium abrahamseni n. sp. is proposed. Histological analysis of intestinal tissue identified large numbers of Cryptosporidium organisms along the epithelial lining of the intestine. Sequence and phylogenetic analysis at 18S rRNA (18S) and actin loci conducted on intestinal scrapings revealed that C. abrahamseni n. sp. was genetically distinct from other Cryptosporidium species. At the 18S locus, it was most closely related to C. huwi (3.2% genetic distance) and exhibited genetic distances ranging from 5.9 to 6.5% (C. molnari) to 14.9% (C. scolpthalmi) from all other Cryptosporidium species. At the actin locus, the genetic distances were larger and C. abrahamseni n. sp. exhibited 10.3% genetic distance from C. huwi, and 17.6% (C. molnari) to 28% (C. canis) genetic distance from other Cryptosporidium spp. Phylogenetic analysis of concatenated 18S and actin sequences confirmed that C. abrahamseni n. sp. shares the closest genetic relationship with C. huwi (6.7% genetic distance), while the genetic distance between C. abrahamseni n. sp. and other Cryptosporidium spp. ranged from 12.1% (C. molnari) to 20.4% (C. canis). Based on genetic and histological data, C. abrahamseni n. sp. is validated as a separate species.

Tetra disseminated microsporidiosis: a novel disease in ornamental fish caused by Fusasporis stethaprioni n. gen. n. sp.

A novel microsporidial disease was documented in two ornamental fish species, black tetra Gymnocorymbus ternetzi Boulenger 1895 and cardinal tetra Paracheirodon axelrodi Schultz 1956. The non-xenoma-forming microsporidium occurred diffusely in most internal organs and the gill, thus referring to the condition as tetra disseminated microsporidiosis (TDM). The occurrence of TDM in black tetra was associated with chronic mortality in a domestic farmed population, while the case in cardinal tetra occurred in moribund fish while in quarantine at a public aquarium. Histology showed that coelomic visceral organs were frequently necrotic and severely disrupted by extensive infiltrates of macrophages. Infected macrophages were presumed responsible for the dissemination of spores throughout the body. Ultrastructural characteristics of the parasite developmental cycle included uninucleate meronts directly in the host cell cytoplasm. Sporonts were bi-nucleated as a result of karyokinesis and a parasite-produced sporophorous vesicle (SPV) became apparent at this stage. Cytokinesis resulted in two spores forming within each SPV. Spores were uniform in size, measuring about 3.9 ± 0.33 long by 2.0 ± 0.2 µm wide. Ultrastructure demonstrated two spore types, one with 9-12 polar filament coils and a double-layered exospore and a second type with 4-7 polar filament coils and a homogenously electron-dense exospore, with differences perhaps related to parasite transmission mechanisms. The 16S rDNA sequences showed closest identity to the genus Glugea (≈ 92%), though the developmental cycle, specifically being a non-xenoma-forming species and having two spores forming within a SPV, did not fit within the genus. Based on combined phylogenetic and ultrastructural characteristics, a new genus (Fusasporis) is proposed, with F. stethaprioni n. gen. n. sp. as the type species.

Species delimitation of Gyrodactylus (Monogenea: Gyrodactylidae) infecting the southernmost cyprinids (Actinopterygii: Cyprinidae) in the New World.

The genus Gyrodactylus von Nordmann, 1832 represents one of the most diverse and widespread taxa within Monogenea, with approximately 500 species described worldwide. Thirty-three species of Gyrodactylus have been recorded in Mexico, and in the last two decades, at least 26 new species have been described mainly from freshwater fish families such as poeciliids, goodeids, profundulids, characids, and cichlids. In this study, we describe two new species of Gyrodactylus infecting freshwater cyprinids based on morphological and molecular characteristics. Gyrodactylus ticuchi n. sp. and Gyrodactylus tobala n. sp. were recovered from Notropis moralesi de Buen and N. imeldae Cortés, respectively, captured in five localities from the State of Oaxaca, Mexico. The new species differ slightly from their congeners in the morphology of the haptoral hard parts and the male copulatory organ. Sequences of the Internal Transcribed Spacers rDNA (ITS1-5.8S-ITS2), cytochrome oxidase subunit I (cox1), and the D2 + D3 domains of the large subunit (28S rDNA) were obtained from multiple specimens and analyzed using Maximum Likelihood (ML) and Bayesian Inference (BI). Phylogenetic hypotheses using ITS rDNA, cox1, and 28S rDNA genes recovered two new species of Gyrodactylus from N. moralesi and N. imeldae; we briefly discuss their phylogenetic relationship with other congeners. These gyrodactylids represent the first species described in species of Notropis from southern Mexico, the cyprinids exhibiting the southernmost distribution in the New World.

The life cycle of Magnivitellinum saltaensis n. sp. (Digenea: Alloglossidiidae) in Salta Province, Argentina.

We describe the alloglossiid trematode Magnivitellinum saltaensis n. sp., a parasite of the characiform fish Psalidodon endy, and its life cycle from Salta, northwest of Argentina. This is the first life cycle described for a species belonging to the genus Magnivitellinum. Cercariae emerged naturally from Biomphalaria tenagophila snails and infected experimentally exposed larvae of Diptera and Ephemeroptera as second intermediate hosts. These larvae in turn were exposed to commercially raised fish, and adults were recovered from characiform albino fish Gymnocorymbus ternetzi. Molecular analysis of natural and experimental adults showed the same genetic sequence for the partial region of 28S rDNA, thus confirming conspecificity. Comparison of these sequences with those published for M. simplex from Mexico showed 1.45% divergence, indicating that the specimens found in Salta belong to a different species, the third described of Magnivitellinum, in agreement with morphological data, geographical location, and host species composition. The new species is distinguished by its small body, vitelline follicles extending from the mid-level of the ventral sucker, Y-shaped excretory vesicle, and presence of papillae around the mouth.

A new species of Wallinia Pearse, 1920 (Digenea: Allocreadiidae), in Astyanax bimaculatus (Linnaeus, 1758) (Characidae) in Northeast Brazil, based on morphology and DNA sequences.

Wallinia caririensis n. sp. is described from the intestine of Astyanax bimaculatus (Linnaeus, 1758) (Characidae) collected in the Batateiras River in the municipality of Crato, Ceará state, Brazil. The description was based on integrative taxonomy approach using DNA sequences from the D1-D3 domains of the 28S rDNA gene. The new species was confirmed through the phylogenetic analysis of the 28S rDNA gene, which showed that Wallinia caririensis n. sp. is a sister taxon of Wallinia brasiliensis (Dias, Müller, Almeida, Silva, Azevedo, Pérez-Ponce de León, and Abdallah, 2018, and Wallinia anindoi Hernández-Mena, Pinacho-Pinacho, García-Varela, Mendonza-Garfias, and Pérez-Ponce de León, 2019), a species which parasitizes Astyanax fasciatus (Cuvier, 1819), A. lacustris (Lucena and Soares, 2016) in Brazil, and A. aeneus (Günther, 1860) in Mexico, with genetic divergences of 2% and 3%, respectively. The new species can be distinguished morphologically from its congeners by possessing large body size (length and width) and tapered extremity in the posterior end of the body, eyespots are present at the pharynx level, and vitelline follicles reach up to the half distance between the posterior testis and the extremity of the body, by having larger testes distributed in coincident zones (i.e., contiguous) and non-operculated eggs (a conspicuous characteristic in W. brasiliensis). To date, species of this genus have already been described in freshwater fishes from Mexico, Costa Rica, Venezuela, and Southeastern Brazil. The species described in this study consists of the second species parasitizing characids in Brazil, and the first record in Northeastern Brazil. This finding fills a gap and expands the biogeographic distribution of the genus Wallinia in South America.

Morphological and phylogenetic characterisation of Unicauda tavaresii n. sp. (Myxosporea: Myxobolidae): a parasite of the circumorbital tissue of the eye of two characiform fishes from the Amazon region of Brazil.

Myxozoans of the family Myxobolidae are common parasites in fish. The diversity and ecology of the species of the genus Unicauda are poorly known, which hampers the understanding of the distribution and prevalence of this group of parasites. In the present study, cysts containing parasites whose morphology was consistent with the genus Unicauda were found in the circumorbital region of the ocular conjunctiva of the freshwater fish Moenkhausia grandisquamis Müller & Troschel, 1845 (Characiformes: Characidae) and Triportheus angulatus Spix & Agassiz, 1829 (Characiformes: Triportheidae). The spores have an oval body and long caudal appendage, with a mean total length of 65.2 ± 5.9 µm and width of 5.2 ± 0.7 µm, with two oval and symmetrical polar capsules of 4.9 ± 0.5 µm in length and 1.4 ± 0.2 µm in width, containing polar filaments with five or six coils. An integrated comparative analysis of the morphological characteristics of this parasite and partial sequences of the SSU rDNA gene supported the identification of a new species of histozoic parasite of the genus Unicauda found in fish from the Tocantins River basin, in the eastern Brazilian Amazon region. The new species was denominated by Unicauda tavaresii n. sp.

Three new species of Anacanthorus Mizelle & Price, 1965 (Monogenea: Dactylogyridae) from Markiana nigripinnis Perugia (Actinopterygii: Characidae) in Pantanal wetlands, Brazil.

Three monogenean species, Anacanthorus luquei n. sp., A. scholzi n. sp. and A. cohenae n. sp. are described from the gills of the tetra fish Markiana nigripinnis (Perugia) (Characidae), collected in the Pantanal wetlands, State of Mato Grosso do Sul, Brazil. Among other differences, Anacanthorus luquei n. sp. differs from the most morphologically similar species, based on the structure of the accessory piece as follows: branches with smooth margins (vs with irregular margins in A. cuticulovaginus), without pointed projections at distal end (vs with projections in A. dipelecinus) and with 2 branches (vs 3 in A. quinqueramus). Anacanthorus scholzi n. sp. is most morphologically similar to A. luquei n. sp., differing from it because one of the branches of the accessory piece is bifurcated at the distal portion. Anacanthorus cohenae n. sp. can be differentiated from the congeners based on the combination of the following features: MCO cylindrical and robust with sclerotised flanges on the extremities, accessory piece V-shaped, bearing two branches similar in length and with blunt distal ends, and hooks with a proximal bulb. This is the first parasitological study on M. nigripinnis and, currently, Anacanthorus allocates 88 species infesting characiform fishes in the Neotropical region, including the three new species described here.

A new species, Henneguya lacustris n. sp. (Cnidaria: Myxosporea), infecting the gills of Astyanax lacustris from Brazil.

The present study describes Henneguya lacustris n. sp. parasitizing Astyanax lacustris (Lütken 1875), from the Tietê River, State of São Paulo, Brazil, through morphological and molecular analysis. Myxospores of the parasites were found in the gills of A. lacustris with 13% prevalence of infection. The myxospores were oval and presented as measures (mean ± standard deviation): total length 18.3 ± 2.2 µm, body length 10.4 ± 1.6 µm, body width 4.9 ± 0.9 µm, tail length 7.2 ± 2.5 µm. The polar capsule was 4.8 ± 0.3 µm long and 1.5 ± 0.2 µm wide. The polar tubules, present inside the polar capsules, had 6 to 7 turns. The ultrastructural analysis allowed the observation of the asynchronous development of the myxospores. Phylogenetic analysis showed H. lacustris n. sp. as a sister species of H. chydadea Barassa and Cordeiro 2003 in a subclade formed by species that parasitize the gills of Characiform fish from Brazil. Using molecular and morphological characterization, this parasite was identified as a new species of the genus Henneguya Thélohan 1892.

A new species of Creptotrematina (Trematoda: Allocreadiidae) from characid fishes of Brazil: morphological and molecular data.

A new species of Creptotrematina Yamaguti, 1954 was collected from characid fishes, Astyanax fasciatus (Cuvier, 1819) and Astyanax lacustris Lucerna & Soares, 2016 from the Batalha River in the State of Sao Paulo, Brazil. The new species most closely resembles Creptotrematina aguirrepequenoi, but differs by the elongated shape of vitelline follicles, the extension of these follicles in the posterior end of body and the fact that they are not confluent. The morphological differences were confirmed through molecular data. Three specimens were sequenced, and molecular analyses were based on the internal transcribed spacers 2 and D1-D3 domains of the 28S ribosomal RNA gene. The obtained topologies showed the new species as a sister taxon of C. aguirrepequenoi, a species originally described from Astyanax mexicanus in Mexico, and later found in Astyanax aeneus in Costa Rica. Isolates of the new species are reciprocally monophyletic, and genetic distance values are similar to those observed in other species pairs within Allocreadiidae. These findings corroborate that the genus Creptotrematina is mostly a parasite of characids, and widely extended across the Americas, with representative species occurring between Argentina and northern Mexico.

Prosthenhystera gattii n. sp. (Digenea: Callodistomidae), a gallbladder parasite of Bryconamericus ikaa from the lower Iguazú River, described based on combined molecular and morphological evidence.

Adult forms of members of the Callodistomidae always parasitize the gallbladder of freshwater fishes and occur in Africa and America. This study provides a description of a new South American species belonging in Prosthenhystera from the gallbladder of a characid fish (Bryconamericus ikaa), and ribosomal gene sequences (28S rDNA and ITS1-5.8S-ITS2) are used to demonstrate molecular differences between the new species and congeners as well as explore interrelationships among congeners. Additionally, the first cytological analysis is conducted for a member of the family to determine chromosome number and arrangement. Prosthenhystera gattii n. sp. most closely resembles Prosthenhystera caballeroi in morphology, but the vitellarium is more extensive reaching anterior to the caecal bifurcation in the new species and the uterus is confined to the hindbody in P. gattii n. sp., whereas it extends to the level of the pharynx in P. caballeroi. Also, the testes, cirrus sac, seminal receptacle and the ratio of body length to width are larger in P. gattii n. sp. Independent Bayesian inference analyses of 28S rDNA and ITS1-5.8S-ITS2 sequence fragments produced phylograms that showed P. gattii n. sp. is more similar to Prosthenhystera obesa + Prosthenhystera oonastica than P. caballeroi + two unidentified species of Prosthenhystera, but with poor posterior probability support for the node in the ITS1-5.8S-ITS2-based phylogram. Further, the genetic distance between P. oonastica and P. gattii n. sp. are the largest among Prosthenhystera spp. Cytological analysis revealed ten metacentric chromosomes, which is fewer than the 12-18 chromosomes present in species from the closely related Gorgoderidae.

A New Species of Rhinergasilus Boeger et Thatcher, 1988 (Copepoda: Ergasilidae) from Gills of Astyanax fasciatus (Cuvier, 1819) (Actinopterygii: Characidae).

PURPOSE: To describe a new species of a parasitic copepod, Rhinergasilus digitus n. sp. (Cyclopoida, Ergasilidae), collected from the gills of the red-tailed lambari Astyanax fasciatus (Characiformes, Characidae) in two tributaries of the Jurumirim Reservoir (Upper Paranapanema River), São Paulo State, Brazil: Ribeirão dos Veados and Paranapanema River. METHODS: Fish were collected using multi-panel gills nets. The gill of each fish was washed and examined in a stereo microscope for copepods. The copepods found were stored in 70% ethanol, cleared in lactic acid, and mounted in Hoyer's medium. Drawings were made with the aid of a Leica microscope DMLS equipped with a drawing tube. RESULTS: The new species differs from its congeneric species, Rhinergasilus piranhus (type-species), in having comparatively biggest body size (body length: 535-598 µm in the new species vs. 237-282 µm in R. piranhus); second antennary segment armed with a minute sensillum near middle of inner margin and a row of spinules on outer margin; third exopodal segment of leg 1 with digitiform process; interpodal plates two and three both ornamented with spinules along posterior margin; leg 5 reduced and represented by two unequal setae. CONCLUSIONS: Based on the morphological differences described above, we erected a new species of Rhinergasilus. Rhinergasilus digitus n. sp. is the second ergasilid described from A. fasciatus, as well as it represents the first report of this genus in a characid fish.

Myxobolus sp. (Myxozoa; Myxosporea) causing asymptomatic parasitic gill disease in Astyanax aff. bimaculatus (Characiformes; Characidae) in the Tocantins river basin, amazon region, Brazil / Myxobolus sp. (Myxozoa; Myxosporea) causando doença parasitária assintomática nas brânquias em Astyanax aff. bimaculatus (Characiformes; Characidae) na bacia do rio Tocantins, região amazônica, Brasil

Abstract The middle course of the Tocantins river is located in the eastern portion of the "Legal Amazon" region of Brazil and the Dantas river is one of its tributaries. Among the components of the aquatic biota, eukaryote microparasites establish direct relationships with several species of fish and have zoonotic potential that is still little known. Myxozoans stand out among these parasites: they cause myxosporidiosis, a disease that gives rise to high mortality rates worldwide. The genus Myxobolus accounts for the largest number of species that have been described. Thirty specimens of Astyanax aff. bimaculatus that had been caught in the Dantas river were examined. The prevalence of cysts with spores morphologically compatible with myxozoans of the genus Myxobolus in the arcuate and gill filaments of these specimens was 20%.

Resumo O curso médio do rio Tocantins está localizado na porção leste da região da "Amazônia Legal" do Brasil, e o rio Dantas é um dos seus afluentes. Dentre os componentes da biota aquática, os microparasitos eucarióticos estabelecem relações diretas com várias espécies de peixes e possuem potencial zoonótico ainda pouco conhecido. Os mixozoários destacam-se entre esses parasitos causando mixosporidiose, doença que dá origem a altas taxas de mortalidade em todo o mundo. O gênero Myxobolus é responsável pelo maior número de espécies descritas de mixozoários. Trinta espécimes de Astyanax aff. bimaculatus capturados no rio Dantas foram examinados. A prevalência de cistos com esporos morfologicamente compatíveis com mixozoários do gênero Myxobolus nos filamentos arqueados e branquiais desses espécimes foi de 20%.

Myxobolus sp. (Myxozoa; Myxosporea) causing asymptomatic parasitic gill disease in Astyanax aff. bimaculatus (Characiformes; Characidae) in the Tocantins river basin, amazon region, Brazil.

The middle course of the Tocantins river is located in the eastern portion of the "Legal Amazon" region of Brazil and the Dantas river is one of its tributaries. Among the components of the aquatic biota, eukaryote microparasites establish direct relationships with several species of fish and have zoonotic potential that is still little known. Myxozoans stand out among these parasites: they cause myxosporidiosis, a disease that gives rise to high mortality rates worldwide. The genus Myxobolus accounts for the largest number of species that have been described. Thirty specimens of Astyanax aff. bimaculatus that had been caught in the Dantas river were examined. The prevalence of cysts with spores morphologically compatible with myxozoans of the genus Myxobolus in the arcuate and gill filaments of these specimens was 20%.

A New Genus of Ergasilidae (Copepoda: Cyclopoida) from the Gills of Astyanax fasciatus (Cuvier, 1819) (Actinopterygii: Characidae).

PURPOSE: To describe a new genus and a new species of an ectoparasitic ergasilid (Copepoda, Ergasilidae) parasite of the red-tailed lambari, Astyanax fasciatus, from Jurumirim Reservoir (Upper Paranapanema River), São Paulo State, Brazil. METHODS: The host fish were collected using multi-panel gill nets. The gill of each fish was washed and examined in a stereo microscope for copepods. The copepods found were stored in 70% ethanol, cleared in lactic acid, and mounted in Hoyer's medium. Some specimens were dissected in glycerol medium and then each dissected part was mounted on individual slides. RESULTS: A new genus and a new species of Ergasilidae were described herein. Duoergasilus basilongus n. gen., n. sp. differs from all other ergasilids in having the second and third pair of biramous swimming legs (P2 and P3) each with a 2-segmented endopod, and by its unique maxillary basis, resembling a whip. CONCLUSIONS: The new copepod is the first 'four-legged' ergasilid with all swimming legs having a 2-segmented endopod. Duoergasilus basilongus n. sp. represents the first record of a parasitic copepod on A. fasciatus in Jurumirim Reservoir, as well as its represents the first description to species level of an ergasilid infecting an Astyanax species in Brazil. A key to the 28 accepted genera of Ergasilidae is provided.

Community structure of metazoan parasites in Hemibrycon surinamensis (Characidae) from the Matapi River in the State of Amapá, Brazil.

The aim of this study was to investigate the community of metazoan parasites in Hemibrycon surinamensis from the Matapi River, State of Amapá, Brazil. Among the 31 examined fish, 77.4 % were parasitized by Jainus hexops, Tereancistrum ornatus (Monogenea), Contracaecum sp. (Nematoda), Clinostomus marginatum and Posthodiplostomum sp. (Digenea). However, the dominance was of monogeneans J. hexops and T. ornatus, and among the endoparasites, the predominance was of species at the larval stage. The parasites showed random dispersion. Brillouin diversity index varied from 0 to 0.9, evenness from 0 to 0.7 and species richness from 0 to 3 parasites per host. Low levels of parasitic infection were observed and discussed. The results indicate that this intermediate host occupies a low position in the food web. This is the third eco-epidemiological study for H. surinamensis.

Interannual and Seasonal Variation in Protozoan and Metazoan Parasite Communities of Hemibrycon surinamensis, a Characid Fish Inhabiting the Brazilian Amazon.

INTRODUCTION: Few studies on the effects of rainy/dry cycle and interannual variation in parasites of Amazonian fish have been carried out. We investigated the influence of interannual variation and seasonality on the community structure and infracommunities of parasites in Hemibrycon surinamensis in a tributary of the Amazon River, in northern Brazil. MATERIALS AND METHODS: The fish were examined for the presence of ectoparasites and endoparasites. RESULTS: In 2011, 9 parasite species were found (2 Protozoa, 2 Monogenea, 1 Digenea, 2 Nematoda and 2 Crustacea), and in 2016, 10 parasite species (3 Protozoa, 2 Monogenea, 1 Digenea, 3 Nematoda and 1 Pentastomida). No qualitative or quantitative dissimilarity in the component communities of parasites was observed between 2011 and 2016, but Brillouin Diversity Index, species richness and evenness were higher in 2016, while Berger-Parker dominance was higher in 2011. In both years, Ichthyophthirius multifiliis and Piscinoodinium pillulare were predominated. Some few species of parasites had interannual (P. pillulare and Genarchella genarchella) and seasonal (Trichodina sp., I. multifiliis, P. pillulare and J. hexops) variation patterns. Species richness of parasites was higher in the dry season, but Brillouin diversity, evenness and Berger-Parker dominance were similar between the seasons. Such seasonal variations were due to the host's the availability of infectious stages of parasites with direct life cycle. CONCLUSIONS: Variations due to seasonal dry/rainy cycle, which influenced the availability of infective stages of parasites, and host size are the factors causing the changes interannual.

Diversity of Rhabdochona mexicana (Nematoda: Rhabdochonidae), a parasite of Astyanax spp. (Characidae) in Mexico and Guatemala, using mitochondrial and nuclear genes, with the description of a new species.

Among fish parasitic nematodes Rhabdochona is one of the most speciose genera, with c. 100 species. Twelve congeneric species occur in Mexican freshwater fishes, in a region located between the Nearctic and Neotropical biogeographical regions. Host association and biogeographical history have determined the high species richness of Rhabdochona in Mexico. One of these species, Rhabdochona mexicana, is highly specific to the characid genus Astyanax. Characids are a group of freshwater fish with Neotropical affinity. In this paper, we explore the genetic diversity of R. mexicana through samples obtained from populations of Astyanax spp. across river basins of Mexico and Guatemala. Sequences of one mitochondrial and two ribosomal genes were obtained from 38 individuals and analysed using Maximum Likelihood and Bayesian Inference analysis. Phylogenetic analyses using cox1, and a concatenated alignment of 18S + 28S + cox1 recovered two genetic lineages. One of them corresponded with R. mexicana sensu stricto; this lineage included three reciprocally monophyletic subgroups; the other lineage was highly divergent and represented a putative candidate species. A detailed morphological study was conducted to corroborate the molecular findings. We describe a new species herein and discuss the implications of using molecular tools to increase our knowledge about the diversity of a speciose genus such as Rhabdochona.

Metazoan endoparasites of Brycon orbignyanus (Characidae: Bryconinae) in a neotropical floodplain

Species richness and composition are central themes in community ecology of helminths because they improve the understanding of factors that determine community structure. Floodplain ecosystems and the environmental alterations induced by hydrological cycles are factors that maintain biodiversity over time, as observed in the Upper Paraná River floodplain, where the individuals of Brycon orbignyanus were collected. The objective of this study was to evaluate whether variables such as the richness and abundance of endoparasites are related to the fish size during different hydrological periods (high and low waters). A total of 163 endoparasites belonging to 13 species were collected in the 104 fish examined. Fish size had a positive correlation with mean diversity and abundance of the endoparasite infracommunity, supporting the idea that larger hosts are able to harbor a more abundant and diverse parasite infracommunity. The diversity of habitats provided by the floodplain can be considered the main factor explaining the differences between these attributes of parasite species. Variations in parasite richness between different hosts provide not only a good model for studies on community diversification but are also of great interest in species conservation. All parasite species found in B. orbignyanus were recorded for the first time in this host, especially in the Upper Paraná River floodplain.