Biodiversity of nematode parasites of Myloplus tiete (Characiformes, Serrasalmidae) from the Paraná River, Southeastern Brazil

• Grant number: 25/19166-3
• Support Opportunities: Regular Research Grants
• Start date: February 01, 2026
• End date: January 31, 2027
• Field of knowledge: Biological Sciences - Parasitology - Helminthology of Parasites
• Principal Investigator: Aline Cristina Zago
• Grantee: Aline Cristina Zago
• Host Institution: Faculdade de Ciências (FC). Universidade Estadual Paulista (UNESP). Campus de Bauru. Bauru , SP, Brazil
• City of the host institution: Bauru
• Associated research grant: 24/00733-2 - Characterization of parasitic fauna and genetic variability of Myloplus tiete from the Paraná River, State of São Paulo, Brazil, AP.R
• Associated scholarship(s): 26/00492-0 - Biodiversity of nematode parasites of Myloplus tiete (Characiformes, Serrasalmidae) from the Paraná River, Southeastern Brazil, BP.IC

Abstract

Neotropical freshwaters harbor much of the world's rich and diverse fish fauna, represented by a wide range of morphological, physiological, ecological, and reproductive attributes. Among the species found is Myloplus tiete, popularly known as "pink pacu" or "silver pacu," which is native to South America and found throughout the Paraná and Paraguay river basins. It is medium-sized, reaching a maximum length of 32.5 cm, and has a herbivorous diet, feeding on terrestrial plants, fruits during the rainy season, and aquatic plants during the dry season. According to the "Red Book of Brazilian Fauna Threatened with Extinction," it is classified as "Endangered" and is listed as a target species in the National Action Plan for the Conservation of Endangered Aquatic Fauna Species of the Mogi/Pardo/Sapucaí-Mirim/Grande Ecosystem. Fish are susceptible to a wide range of parasitic infections, with nematodes representing one of the most important groups of metazoan parasites of Neotropical fish. Their life cycle varies depending on the species, and some may require one or more hosts to complete their development. Fish can act as definitive or intermediate hosts. In the former, adult nematodes primarily parasitize the digestive tract, and in the latter, larval forms can remain encysted or migrate to various organs, causing significant lesions. Regarding parasitism in M. tiete, there are only two studies in the literature conducted with this fish species, both of which report the presence of the nematode Ichthyouris voltagrandensis parasitizing the intestine. Therefore, accurate identification of parasite species is essential to understanding their distribution and interactions with hosts. Furthermore, considering the threat level and the limited number of studies related to parasitological aspects of this fish species, it is important to conduct research focusing on this species to expand biological knowledge about it and to assist in the development of strategies for its preservation, conservation, and management, since parasitism can affect the health and development of these hosts. Therefore, this project aims to characterize the biodiversity of nematode parasites of M. tiete from the Paraná River, São Paulo State, Brazil. Thirty specimens of M. tiete from the reservoir of the "Engenheiro Souza Dias" Hydroelectric Power Plant (Jupiá) on the Paraná River, between the cities of Castilho, São Paulo, and Três Lagoas, Mato Grosso do Sul, will be analyzed. In the laboratory, the fish will be necropsied and examined under a stereomicroscope for the presence of nematodes. The nematodes found will be collected and fixed in 70% ethyl alcohol. Nematode biodiversity will be characterized through morphological and morphometric analyses, in addition to parasitological attributes. For morphological analysis, nematodes will be diaphanized with Amann's lactophenol to observe structures of systematic value. Subsequently, they will be analyzed in a computerized image analysis system, where morphometric analysis of the structures of systematic value will be performed, as well as photomicrographs. Morphological identification of nematodes will be performed at the lowest taxonomic level possible, aided by identification keys, reference guides, scientific articles, and other specialized literature. After identification, parasitological attributes will be calculated for each nematode species found, such as prevalence, mean intensity of infection, and mean abundance. (AU)