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The present study describes three new species of monogenean parasites of characid fishes from the Upper Paraná River basin, Brazil: Characithecium paranapanemense n. sp. on Psalidodon paranae and Psalidodon bockmanni, Diaphorocleidus magnus n. sp. on Astyanax lacustris and Psalidodon fasciatus, and Diaphorocleidus neotropicalis n. sp. on Astyanax lacustris and P. bockmanni. An amendment for Diaphorocleidus is proposed, since additional characters observed in the new species required to extend the generic diagnostic features mainly to include: articulation process connecting the base of the MCO with accessory piece present or absent, and accessory piece with variable shapes (plate-like, pincer-shaped, wrench-shaped, sheath-shaped), divided or not into subunits. Characithecium paranapanemense n. sp. can be distinguished from other congeners by the morphology of its MCO and accessory piece. Diaphorocleidus magnus n. sp. differs from most of its congeners by the morphology of its accessory piece, the presence of articulation process connecting the base of the MCO with accessory piece, and the morphology of the sclerotized structures of the haptor. Diaphorocleidus neotropicalis n. sp. can be easily distinguished from its congeners by the morphology of the accessory piece, the sclerotized structures of the haptor and the morphology of the vagina. Molecular data of the new species (partial 28S rDNA and mitochondrial cytochrome oxidase I) were obtained and the first phylogenetic analysis based on 28S rDNA gene sequences for species of Characithecium and Diaphorocleidus are provided. Although Diaphorocleidus and Characithecium share some morphological similarities, phylogenetic analysis indicates that species of these two genera are not closely related., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Diversity of Creptotrema was investigated using morphological and molecular tools, including data for Creptotrema creptotrema (type-species). Three new species, parasites of Brazilian fishes, are described: Creptotrema conconae n. sp. (type-host, Imparfinis mirini Haseman), Creptotrema schubarti n. sp. (type-host, Characidium schubarti Travassos) and Creptotrema megacetabularis n. sp. (type-host, Auchenipterus osteomystax (Miranda Ribeiro)). The diagnosis of the genus was amended to include new features. The new species differ from each other mainly in terms of body shape, relative sucker size, and testes position. DNA sequences were obtained from Creptotrema spp. from Brazil, including 28S, ITS and COI. Genetic divergences among the new species and C. creptotrema varied from 2.1 to 5.2% (21-49 bp) for 28S, and 6.6 to 16.4% (21-45 bp) for COI. Phylogenetic analysis (28S) placed the newly generated DNA sequences of Creptotrema in a clade (Creptotrema clade sensu stricto) composed of C. creptotrema, the new species described herein, and all species previously described as Auriculostoma, revealing that Auriculostoma is best interpreted as a synonym of Creptotrema based on the principle of priority of zoological nomenclature. Creptotrema funduli, the single sequence of the genus previously available, was not grouped within the Creptotrema clade sensu stricto, suggesting the need for reevaluation of the taxonomic status of this species. Our results showed that Creptotrema represents a monophyletic genus of trematodes widely distributed across the Americas, which currently comprises 19 valid species of parasites of teleosts and anurans., (© L. Franceschini et al., published by EDP Sciences, 2021.)

This study describes two new species, Trinigyrus anthus n. sp. and Trinigyrus carvalhoi n. sp., from gills of Hypostomus spp. from the Upper Paraná River basin, Brazil. Trinigyrus peregrinus is redescribed based on examination of its holotype, paratypes and new material of specimens parasitizing Pterygoplichthys ambrosettii, also from the Upper Paraná River basin, Brazil. New morphological features were included in the diagnosis of the genus, such as the presence of a sclerotized border on the anchor base, and a weakly sclerotized fringe on the base of the male copulatory organ (MCO). Trinigyrus anthus n. sp. differs from other congeners by the shape of the MCO, presenting an enlarged base with sclerotized fringes resembling flower petals. Trinigyrus carvalhoi n. sp. and T. peregrinus are similar but can be differentiated from each other mainly by the sclerotization of the vagina (absent in the new species), and the morphology of the MCO (C-shaped versus one counterclockwise circle, respectively). For the first time, gene sequences of Trinigyrus spp. from Brazil were obtained (partial ribosomal 28S and mitochondrial cytochrome c oxidase I (mtCOI)). The genetic divergences among the new species and T. peregrinus varied from 2 to 3% (6‒18 pb) based on sequences of 28S ribosomal DNA (rDNA), and 6-7% (83‒92 pb) using mtCOI. Phylogenetic analyses based on partial 28S rDNA revealed that Trinigyrus, Heteropriapulus and Unilatus formed a monophyletic and well-supported clade of monogeneans from Neotropical freshwater loricariids, suggesting a closer relationship among these dactylogyrids and their hosts.

The present study describes Demidospermus spirophallus n. sp. and Demidospermus prolixus n. sp. (Monogenea, Dactylogyridae) from the siluriform catfish Loricaria prolixa Isbrücker & Nijssen, 1978 (Siluriformes, Loricariidae) from the state of São Paulo, Brazil, supported by morphological and molecular data. In addition, notes on the circumscription of the genus with a redescription of Demisdospermus anus are presented. Demidospermus spirophallus n. sp. differed from other congeners mainly because of the morphology of the male copulatory organ (MCO), which exhibited 2½ counterclockwise rings, a tubular accessory piece with one bifurcated end and a weakly sclerotized vagina with sinistral opening. Demidospermus prolixus n. sp. presents a counterclockwise-coiled MCO with 1½ rings, an ovate base, a non-articulated groove-like accessory piece serving as an MCO guide, two different hook shapes, inconspicuous tegumental annulations, a non-sclerotized vagina with sinistral opening and the absence of eyes or accessory eyespots. The present study provides, for the first time, molecular characterization data using the partial ribosomal gene (28S) of two new species of Demidospermus from Brazil (D. spirophallus n. sp. and D. prolixus n. sp.), and Demidospermus anus from Loricariichthys platymetopon Isbrücker & Nijssen, 1979 collected in the Upper Paraná River floodplain, Brazil. Additionally, a revision of the species composition of this genus and others that occur in catfish is proposed to elucidate problems with their circumscription. The Brazilian species of Demidospermus clustered together as sister taxa among Neotropical dactylogyrids from siluriforms. The morphological characterization of D. spirophallus n. sp. and D. prolixus n. sp., and the molecular data of the three species in the present study will extend knowledge about this monogenean genus from the Neotropical region, and provide new information for future phylogeny studies.

This study reports the occurrence of Austrodiplostomum compactum metacercariae in the freshwater fish Schizodon intermedius (ximborê/piava) from a Neotropical reservoir in the Paranapanema River, state of São Paulo, Brazil. From a total of 75 fish collected, we found 38 infected with A. compactum metacercariae (prevalence = 50.67%) in the eyes. The mean intensity of infection and mean abundance were 9.05 ± 4.26 (1-155) and 4.59 ± 2.20 (0-155), respectively. Poulin's Discrepancy Index was 0.87 and four specimens presented more than 10 metacercariae in their eyes. No correlation was observed between parasite abundance and standard length, total weight and condition factor (p>0.05). These metacercariae are reported for the first time in S. intermedius.

A complete morphological description, supported by molecular data, of Clinostomum detruncatum metacercariae is reported in this study. The metacercariae were found infecting Synbranchus marmoratus from the Paraná River, municipality of Guaíra, Paraná State, Brazil. The taenioidean uterus is the main morphological characteristic of this species. Both neighbor-joining (NJ) and maximum likelihood (ML) trees showed 2 clear separate clusters grouping together the species from the Palearctic region (Clinostomum complanatum, Clinostomum cutaneum, Clinostomum phalacrocoracis, Clinostomum philippinense) and those from the Nearctic/Neotropical regions (Clinostomum marginatum, Clinostomum tataxumui, C. detruncatum, Clinostomum sp. 7). The latter clade is divided into 2 subclades grouping species from North America and Mexico (C. marginatum and C. tataxumui), and those from Brazil (C. detruncatum and Clinostomum sp. 7).

The development of cage fish farms has been associated with an increase in parasitic diseases. Organic matter resulting from feed waste and faeces attracts animals such as birds and invertebrates that can act as hosts for parasites. The aim of this study was to evaluate the influence of cage farming on Austrodiplostomum compactum metacercariae infections of Plagioscion squamosissimus collected close to a cage farm in the Chavantes reservoir (Paranapanema River). Thirty-seven fish were collected in an area close to cages (CF), and 28 in an area not influenced by cages (CT). All specimens were weighed, measured and the eyes removed for morphological analyses of metacercariae. The prevalence, mean intensity of infection, mean abundance and condition factor were calculated. The prevalence (CF = 86.4%, CT = 57.1%), mean infection intensity (CF = 20.31 ± 1.13, CT = 4.29 ± 7.14) and mean abundance (CF = 17.70 ± 6.27, CT = 2.35 ± 0.77) were higher in the CF (P< 0.05) group. There were no significant correlations (P> 0.05) between the mean abundance and standard length or the total weight and condition factor in either group (P> 0.05). Fish farms may interfere with the life cycle of A. compactum, leading to more infections with P. squamosissimus. This could be due to an increase in the number of host animals that are attracted by the availability of food resources derived from fish farms.

This study reports the infection of fishes by Austrodiplostomum compactum metacercariae in the Chavantes reservoir, medium Paranapanema River, municipality of Ipaussu, São Paulo State, Brazil. Twenty-three fish species were analysed, and 13 were infected with A. compactum metacercariae (56.5%) in their eyes. The following six fish species are new hosts for this metacercaria: Crenicichla haroldoi (1/1), Eigenmannia trilineata (11/6), Hoplosternum littorale (11/1), Iheringichthys labrosus (17/2), Leporinus amblyrhynchus (11/1), and Piaractus mesopotamicus (3/1). These new species increase the number of Brazilian fish species infected with this parasite to 36. Based on these findings, we hypothesise that the metacercariae larval stage of the parasite has a low specificity for the second intermediate host (fish). The majority of fish species infected in Brazil belong to the Loricariidae and Cichlidae families. For the fish species with higher mean abundances in Brazil, six are non-native species, and currently, Plagioscion squamosissimus has the highest mean abundance. The majority of fish species infected with A. compactum in Brazil are concentrated in the Paraná basin, although this may be related to the distribution of researchers.

This study aimed to report the infection by Sphincterodiplostomum musculosum metacercariae in Steindachnerina insculpta from the Chavantes Reservoir, medium Paranapanema River, municipality of Ipaussu, State of São Paulo, Brazil. Thirty specimens of S. insculpta were collected and 29 were infected with S. musculosum metacercariae (prevalence = 96.67%) in the eyes and visceral cavity. The mean intensity of infection and abundance were 96.6 ± 29.41 (7-846) and 93.3 ± 28.6 (0-846), respectively. Positive correlation was observed between parasite abundance in the eyes and standard length (rs = 0.5, p = 0.005), total weight (rs = 0.649, p = 0.0001), and condition factor (rs = 0.439, p = 0.0154). The high parasitism rates by S. musculosum metacercariae in S. insculpta can be an indicative that this fish species is highly susceptible to infection by this diplostomid, and even reflect the presence of a large abundance of the intermediate host. Moreover, S. musculosum metacercariae are reported for the first time in S. insculpta.