Population and Component Community Descriptors of Monopisthocotyla Parasitizing Triportheus spp. (Actinopterygii: Triportheidae) in the Tocantins-Araguaia River Basin, Brazil.

PURPOSE: Monopisthocotyla constitute a diverse group of ectoparasites of Neotropical fish and are recognized as important bioindicators of environmental conditions in aquatic ecosystems. Despite the high biodiversity of the Tocantins-Araguaia basin, studies simultaneously describing the population descriptors and component communities of these parasites in fish of the genus Triportheus are still scarce. This study aimed to characterize the population and component community descriptors of Monopisthocotyla parasitizing Triportheus albus and Triportheus trifurcatus in the Tocantins River, Maranhão, Brazil. METHODS: A total of 262 hosts were examined (69 T. albus and 193 T. trifurcatus). Parasites were collected from the gills, morphologically identified, and evaluated for prevalence, mean intensity, mean abundance, and distribution pattern. Component communities were characterized using species richness, Shannon diversity, Pielou's evenness, Simpson's diversity and dominance, and Berger-Parker dominance. RESULTS: Triportheus trifurcatus showed higher richness, diversity, and evenness, while T. albus displayed higher dominance, mainly due to the high proportional abundance of Jainus spp. Most parasite populations showed an aggregated distribution pattern, and host-related factors exerted limited influence on parasite abundance and richness. The findings demonstrate differences in the organization of component communities between the two host species. CONCLUSIONS: The combined use of population and component community descriptors improved the understanding of the ecological organization of Monopisthocotyla communities parasitizing Neotropical fish. These findings provide baseline information for future biodiversity and environmental monitoring studies in the Tocantins-Araguaia River basin.