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A total of 57 sairus (Cyphocharax nagelii) from the Peixe River, state of São Paulo, southeastern Brazil, were examined between April 2011 and February 2012. Eleven species of metazoan parasites were collected and identified: Palombitrema triangulum, Curvianchoratus hexacleidus, Curvianchoratus singularis, Sphincterodiplostomum musculosum, Contracaecum sp., Cacatuocotyle paranaensis, Cosmoxynemoides aguirrei, Amplexibranchius bryconis, Brasergasilus sp., Ergasilus sp. and Clinostomum sp. The monogenean P. triangulum was the most prevalent species (61.40%) with the highest mean intensity (4.88). The monogeneans C. hexacleidus and C. singularis, the digenean S. musculosum and the nematode Contracaecum sp. also showed high prevalence. Only S. musculosum presented significant correlation between the total body weight of the host and its abundance. The parasitic infracommunities had a mean Brillouin diversity (HB) of 1.165 ± 0.987 and the maximum diversity was 1.671. The sex and length of the hosts did not influence the abundance of any parasite species. The community of metazoans in C. nagelii from the Peixe River was characterized by high richness and low uniformity.Keywords: Fish, Curimatidae, parasites, Peixe River, Brazil. ResumoCinquenta e sete "sairú" (Cyphocharax nagelii) foram examinados entre abril de 2011 e fevereiro de 2012, provenientes do Rio do Peixe, Estado de São Paulo, Sudeste do Brasil. Onze espécies de metazoários parasitos foram coletadas e identificadas: Palombitrema triangulum, Curvianchoratus hexacleidus, Curvianchoratus singularis, Sphincterodiplostomum musculosum, Contracaecum sp., Cacatuocotyle paranaensis, Cosmoxynemoides aguirrei, Amplexibranchius bryconis, Brasergasilus sp., Ergasilus sp., Clinostomum sp. O monogenético P. triangulum foi o parasito mais prevalente (61,40%) e com a maior intensidade média (4,88). Os monogenéticos C. hexacleidus e C. singularis, o digenético S. musculosum e o nematóide Contracaecum sp. também apresentaram alta prevalência. Apenas S. musculosum apresentou correlação significativa entre o peso total do corpo do hospedeiro e sua abundância. As infracomunidades parasitárias tiveram uma diversidade média de Brillouin (HB) =1,165±0,987 e a diversidade máxima foi de 1,671. O sexo e comprimento dos hospedeiros não influenciaram a abundância parasitária. A comunidade de metazoários de C. nagelii no Rio do Peixe foi caracterizada pela alta riqueza e baixa uniformidade.Palavras-chaves: Peixe, Curimatidae, parasitos, Rio do Peixe, Brasil.Cyphocharax nagelii (Steindachner, 1881), known locally as the sairú, is a Curimatidae with geographical distribution restricted to South America, and is found especially in the upper Paraná River basin. The species is involved in large seasonal migration from the Mogi Guaçu River, an upper Paraná River tributary. Young fish aged up to 50 days were reported as being zooplanktivorous, and the larger ones as detritivorous. This species reaches maturity at around the length of 8.9 centimeters for both sexes, and can reach a maxim...

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A total of 53 tamboatás, Hoplosternum littorale, from the Batalha River, São Paulo, southeastern Brazil, were examined between February 2014 to December 2016. Seventeen species of parasites were identified, and 961 specimens were collected . The richness of each community varied from one to seven species of parasites per fish. The metacercariae of Diplostomum lunaschiae showed higher prevalence and mean abundance, being the core species. Gyrodactylus sp. obtained a higher mean intensity value. Aporocotylidae gen. sp. showed a significant negative correlation between its abundance and the standard host weight and length, while Spiroxys sp. showed a significant negative correlation between its abundance and the host weight. Batalha River has importance as a maintainer of local biodiversity with a relevant contribution to the knowledge of freshwater biodiversity in the State of São Paulo. Gyrodactylidae gen. sp., A. mordax, Aporocotylidae gen. sp., D. lunaschiae, Diplostomidae gen. sp. 1, Contracaecum sp., D. renale, Porrocaecum sp., Pseudocapillaria sp. 1, Pseudocapillaria sp. 2, S. contortus, Oligobdella sp., and L. cyprinacea are parasites mentioned for the first time in H. littorale. Aporocotylidae gen. sp., Gyrodactylidae gen. sp., and Oligobdella sp. are new species in process of taxonomic description by the authors of the present study.

A new species of myxozoan, Myxobolus imparfinis n. sp. is described based on material from the gills of Imparfinis mirini (Haseman) (Heptapteridae). Mature myxospores are round, measuring 7.1-8.4 (7.9 ± 0.3) μm in length, 4.5-6.2 (5.5 ± 0.5) μm in width and 3.1-4.2 (3.7 ± 0.3) μm in thickness. The polar capsules are of unequal size, the larger polar capsule measuring 3.4-4.5 (3.9 ± 0.3) μm in length and 1.4-2.0 (1.7 ± 0.1) μm in width and the smaller capsule measuring 3.1-3.8 (3.4 ± 0.2) μm in length and 1.2-1.8 (1.5 ± 0.2) μm in width. The polar filament presents 6-7 coils. Spores had a prevalence of infection of 75% (6/8). In histological analyses we detected the development site of spores in primary filaments, in afferent branchial artery, thus classifying the type of infection to the filamental type and vascular subtype. The phylogenetic analyses of a dataset including species Myxobolus Bütschli, 1882 and Henneguya Thélohan, 1892 from South America recovered M. imparfinis n. sp. as a sister species of Myxobolus flavus Carriero, Adriano, Silva, Ceccarelli & Maia, 2013. To our knowledge, this is the first record of a myxozoan species parasitising I. mirini.