Two species of Cosmetocleithrum Kritsky, Thatcher & Boeger, 1986 (both new) and two species of Demidospermus Suriano, 1983 (one new) are reported from the gills of the catfish Auchenipterus nuchalis, popularly known as “mapará”, from the Tocantins River and tributaries, North Region of Brazil. Cosmetocleithrum berecae n. sp. differs from all other species presently known in the genus by the morphology of the anchors presenting an elongate shaft and short recurved point, a coiled male copulatory organ (MCO) with three rings, and an elongate slender accessory piece with a bifurcated distal end. Cosmetocleithrum nunani n. sp. differs from its congeners by the combination of the following features: (1) Ventral and dorsal anchors with moderately long curved shaft and short point; (2) Hooks with poorly developed thumb; (3) Hook pairs 5 and 6 similar to each other, but morphologically distinct from remaining hook pairs; and (4) MCO coiled, with approximately 1.5 rings. Demidospermus tocantinensis n. sp. is easily distinguished from other species of the genus by presenting an inverted-G-shaped MCO with a median knee-like expansion. Demidospermus osteomystax Tavernari, Takemoto, Lacerda & Pavanelli, 2010 is redescribed based on paratypes and specimens from the gills of A. nuchalis from the Tocantins River, a new host and locality records for this species. The monotypic Paracosmetocleithrum Acosta, Scholz, Blasco-Costa, Alves & Silva, 2017, the only other Neotropical genus reported in siluriforms besides Cosmetocleithrum with species presenting two ribbon-like projections on the posterior margin of the dorsal bar, is considered a junior subjective synonym of Cosmetocleithrum.

In the Amazon, the growing demand for fish has been boosting the expansion of fish farms. However, the intensification of cultivation can generate disequilibrium in the parasite-host environment, predisposing fish to parasitic infections. The objective of this study was to evaluate the community structure of metazoan parasites in cultivation systems of piauçu, Leporinus macrocephalus, in the state of Acre, Brazil. We examined 100 specimens from a semi-intensive cultivation system (earth tanks) and 100 from an extensive system (dams). Overall 66.5% of the hosts were parasitized. We collected 1,240 parasite specimens, classified in 15 metazoan taxa (10 monogenoidean, one digenean and four nematodes). The parasite prevalence was higher by Monogenoidea in the dams, and by Nematoda in the earth tanks. The parasitic indexes were, in general, low and varied among species. Monogeneoidea had higher values for quantitative and ecological descriptors of parasitism in the dams, while Nematoda had higher values in the earth tanks. A single species of Digenea was found in the dams, with low prevalence. No taxon was classified as central. In the dams, parasite abundance was correlated only with total fish length, while in the earth tanks, it was positively correlated with total length, weight and condition factor of fish. The endoparasite and ectoparasite infracommunities presented higher richness, dominance, diversity and evenness, respectively, in the earth tanks and in the dams. This is the first study of ecological descriptors of parasites of L. macrocephalus in the Amazon. KEYWORDS: diversity, Digenea, Monogenoidea, NematodaComunidade de metazoários parasitos de Leporinus macrocephalus (Characiformes: Anostomidae) em sistemas de cultivo no oeste da Amazônia, Brasil RESUMO Na Amazônia, a crescente demanda por pescado vem impulsionando a expansão da piscicultura. No entanto, a intensificação dos cultivos pode gerar desequilíbrio no sistema parasito-hospedeiro-ambiente, predispondo os peixes a infecções parasitárias. O objetivo deste estudo foi avaliar a estrutura das comunidades de metazoários parasitos de piauçu, Leporinus macrocephalus, em sistemas de cultivo no estado do Acre, Brasil. Foram coletados 200 peixes, sendo 100 espécimes de sistema de cultivo semi-intensivo em viveiro escavado e 100 de sistema extensivo em açude. Dos 200 hospedeiros analisados 66,5% estavam parasitados. Foram coletados 1.240 espécimes de metazoários, classificados em quinze espécies (10 de Monogenoidea, uma de Digenea e quatro de Nematoda). A prevalência de parasitismo por Monogenoidea foi maior em açude e por Nematoda em viveiro. De forma geral, os índices de parasitismo foram baixos e variaram entre as espécies, com maiores valores dos descritores quantitativos e ecológicos do parasitismo por Monogenoidea em açude e Nematoda em viveiro. A única espécie de Digenea foi encontrada em açude e com baixa prevalência. Nenhum táxon foi classificado como central. Nos açudes, a abundância parasitária foi correlacionada apenas com o comprimento...

From December 2006 to March 2008, 60 specimens of Paralichthys isosceles and 25 specimens of P. patagonicus were investigated for helminths. One hundred and sixty-nine digeneans were recovered and parasites were identified as juvenile didymozoids of two types. Torticaecum and Neotorticaecum were found in 48 of the 60 P. isosceles (80%) and 10 of the 25 P. patagonicus (40%). Torticaecum and Neotorticaecum are reported for the first time in fish in South America (Brazil), found in the Atlantic Ocean. Morphometrics and illustrations are presented.

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