The aim of this study was to investigate parasites crustacean fauna in ,, ,, ,, ,, ,, and of the State Amapá and Pará, in northern Brazil. A total of 242 parasites, including ,, ,, ,, , and undetermined Lernaeidae, were collected from these hosts. The species had the greatest richness among the community of parasitic crustaceans. There was a low abundance of parasites among the hosts, other than, was most abundant in the integument of and. Finally, the present study reported nine new hosts for the crustacean parasite species and expanded knowledge of the occurrence of some parasite species in the Jari River basin, in eastern Amazon.

Among Kinetoplastida, the Trypanosoma is the genus with the highest occurrence infecting populations of marine fish and freshwater in the world, with high levels of prevalence, causing influences fish health and consequent economic losses, mainly for fish populations in situation stress. This study investigated infections of Hypostomus spp. by Trypanosoma spp. and leeches, as well as blood parameters of this host in the network of tributaries of the Tapajós River in the state of Pará, in the eastern Amazon region in Brazil. Of the 47 hosts examined, 89.4% were parasitized by Trypanosoma spp. and 55.4% also had leeches attached around the mouth. The intensity of Trypanosoma spp. increased with the size of the host, but the body conditions were not influenced by the parasitism. The number of red blood cells, and hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH), total number of leukocytes and thrombocytes showed variations and negative correlation with the intensity of Trypanosoma spp. in the blood of the hosts. The results suggest that the leeches were vectors of Trypanosoma spp. in Hypostomus spp.

Myxozoans are a diverse group of parasitic cnidarians, with some species recognized as serious pathogens to their hosts. The present study describes 2 new myxobolid species (Myxobolus figueirae sp. nov. and Henneguya santarenensis sp. nov.) infecting skin and gill filaments of the Amazonian pimelodid fish Phractocephalus hemioliopterus, based on ultrastructural, histology and phylogenetic analysis. The fish were caught in the Amazon River, Pará, Brazil. The plasmodial development of M. figueirae sp. nov. was in the dermis and those of H. santarenensis sp. nov. were of the intralamellar type. For both species, the plasmodia were surrounded by a connective tissue layer, but there was no inflammatory infiltrate. For M. figueirae sp. nov., mature spores were ovoid measuring 9.1 to 10 (9.5 ± 0.3) µm in length, 5.8 to 6.9 (6.4 ± 0.3) µm in width and 4.4 to 4.5 (4.5 ± 0.1) µm in thickness. Two polar capsules were elongated and of unequal size. For H. santarenensis sp. nov., mature spores were ellipsoidal in the frontal view, measuring 26.3 to 36.1 (31.9 ± 3) µm in total length, 9.6 to 11.9 (10.8 ± 0.5) µm in body length, 3.7 to 4.9 (4.3 ± 0.3) µm in width and 16.6 to 25.6 (21 ± 3.1) µm in caudal process. The polar capsules were elongated and of equal size. Phylogenetic analysis, based on partial small subunit ribosomal DNA (SSU rDNA) sequences and using the closest myxozoan sequences to each one of the species studied here based on previous GenBank data, showed M. figueirae sp. nov. and H. santarenensis sp. nov. clustering in distinct lineages. While H. santarenensis sp. nov. clustered in a well-supported subclade composed of Henneguya species that infect gills of South American pimelodid hosts, M. figueirae sp. nov. clustered in a weakly supported subclade containing parasite species of bryconid hosts.

Traira (Hoplias malabaricus) is a neotropical fish that is widely distributed in freshwater environments in South America. In the present study, we documented the occurrence of metacercariae of Austrodiplostomum spp. (Diplostomidae) in the eyes and cranial cavity of H. malabaricus and described parasite-induced behavioral changes in the host. The fish were collected from the upper São Francisco River, in the Serra da Canastra mountain range, Minas Gerais, transported alive to the laboratory, observed for 2 weeks, and subsequently examined for parasites. Of the 35 fish examined, 28 (80 %) had free metacercariae in the vitreous humor (mean intensity=95.4; mean abundance=76.3), and 24 (68.57 %) had free metacercariae in the cranial cavity, mainly concentrated below the floor of the brain, at the height of the ophthalmic lobe (mean intensity=12.91; mean abundance=8.85). Specimens of H. malabaricus with a high intensity of infection in the brain displayed changes in swimming behavior.