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

• Grant number: 25/19164-0
• Support Opportunities: Regular Research Grants
• Start date: April 01, 2026
• End date: March 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): 26/00869-7 - Biodiversity of digenean parasites of Myloplus tiete (Characiformes, Serrasalmidae) from the Paraná River, Southeastern Brazil, BP.IC

Abstract

Myloplus tiete (Characiformes, Serrasalmidae) is a native fish species found in the upper Paraná River basin, popularly known as "silver pacu." It is medium-sized, reaching up to 32.5 cm in length, and exhibits herbivorous feeding habits. According to the "Red Book of Threatened Brazilian Fauna," it is classified as "Endangered" and is listed as a target species of the National Action Plan for the Conservation of Endangered Aquatic Fauna Species of the Mogi/Pardo/Sapucaí-Mirim/Grande Ecosystem. Fish are the most parasitized group of vertebrates, as the aquatic environment supports several factors of paramount importance for the survival of these organisms, such as propagation, reproduction, and completion of the life cycle. Among these parasites, digenetic trematodes represent one of the most common and abundant groups of metazoans in fish. They have a very complex evolutionary cycle, requiring two or more hosts to complete their life cycle. Fish can act as definitive hosts or second intermediate hosts. In the first case, most adult parasites live in the intestine, although some can also be found in the visceral cavity, within organs such as the gallbladder and gonads, as well as in the circulatory system and subcutaneous tissue. When acting as intermediate hosts, larvae are generally found encysted in various regions, such as the musculature, nervous system, gonads, eyes, and other organs. 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 (Martins, Yoshitoshi & Umekita, 2001) parasitizing the intestine. Therefore, accurate identification of parasite species is essential to understanding their distribution and interactions with hosts. Furthermore, given the threat level and the limited number of studies on parasitological aspects of this fish species, it is important to conduct research focusing on this species to expand biological knowledge and develop strategies for its preservation, conservation, and management, as parasitism can affect the health and development of these hosts. Therefore, this project aims to characterize the biodiversity of digenean 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 to detect the presence of digeneans. The digeneans found will be compressed between slides or between a slide and a coverslip, depending on their thickness, and immersed in cold 70% ethyl alcohol for fixation, then preserved in 70% ethanol. Characterization of the digenean biodiversity will be performed through morphological and morphometric analyses, in addition to analysis of parasitological attributes. For morphological analysis, the digeneans will be stained with the hydrochloric carmine or Mayer's carmalum technique and diaphanized with eugenol 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 the digeneans will be performed at the lowest possible taxonomic level. After identification, parasitological attributes will be calculated for each digenean species found, such as prevalence, mean intensity of infection, and mean abundance. (AU)