The phylum Nematoda is considered one of the most diverse groups in South America, as it is found in all habitats and is dynamic regarding the ecological characteristics of environments, this group becomes important for monitoring the state of ecosystems, thus making it of great importance. Its identification and occurrences in western Amazonia. Thus, the present study aims to present a list of fish nematodes in western Amazonia, as well as to describe their specific hosts. The study was carried out in the Alto Juruá region of the Western Amazon around the municipalities of Cruzeiro do Sul – Acre and Guajará – AM, Brazil. A total of 10,716 fish were collected, belonging to eight orders, 32 families and 216 species, with only 164 species showing nematodes. The species with the highest number of hosts were Procamallanus (S.) inopinatus Travassos et al., (1928), (67), Contracaecum sp....